A group of astronomers have identified a ring of planetary debris orbiting close to a dying star, some 117 light-years away from Earth, hinting at what could be a planet in a habitable zone where life could exist. If confirmed, it would be the first time a life-supporting world is discovered orbiting such a start, known as a “white dwarf.”
While most large stars go supernova at the end of their evolution, medium and small ones with a mass of less than eight times than the one of the Sun usually become white dwarfs. They have a similar carbon and oxygen mass despite their small size. About 97% of the stars in the Milky Way will become white dwarfs, according to a previous study.
A team of researchers measured light from a white dwarf in the Milky Way called WD1054–226 using data from ground and space-based telescopes. They noticed something appeared to be passing regularly in front of the star, causing dips in the light. The pattern repeated every 25 hours, with the biggest dip every 23 minutes.
This indicates that the star is surrounded by a ring of 65 comet-sized or moon-sized orbiting objects, evenly spaced in their orbits by the gravitational pull of a nearby planet the size of Mars or Mercury. The objects are 2.6 million kilometers from the star, putting their temperature at 50ºC – in the middle of the range for liquid water.
“An exciting possibility is that these bodies are kept in such an evenly-spaced orbital pattern because of the gravitational influence of a nearby planet. Without this influence, friction and collisions would cause the structures to disperse, losing the precise regularity that is observed,” lead author Jay Farihi said in a statement.
Tracking white dwarfs
Finding planets orbiting white dwarfs is a massive challenge for astronomers because these stars are much fainter than the main-sequence stars, such as the Sun. So far, astronomers have only last year found tentative evidence of a gas giant, like Jupiter, orbiting a white dwarf. It’s estimated to be one or two times as massive as Jupiter.
For this new study, the researchers focused on WD1054–226, a white dwarf 117 light-years away from Earth. They recorded changes in its light over 18 nights, using a high-speed camera at the observatory La Silla in Chile. They also looked at data from NASA’s Transiting Exoplanet Survey Satellite (TESS) to better interpret changes in the light.
The habitable zone where the potential planet could be located is usually referred as the Goldilocks zone, taken from the children’s fairy tale. Since the concept was introduced in the 1950s, many stars have been shown to have a Goldilocks area. The temperature from the starts have to be just right so liquid water can exist on the surface.
Compared to big stars like the Sun, the habitable zone of white dwarfs is smaller and closer to the star, as white dwarfs emit less heat. The researchers estimated that the structures observed in the orbit were enveloped by the star when it was a red giant, so they are more likely to have formed or arrived recently than having survived the birth of the start.
“The possibility of a planet in the habitable zone is exciting and also unexpected; we were not looking for this. However, it is important to keep in mind that more evidence is necessary to confirm the presence of a planet. We cannot observe the planet directly so confirmation may come by comparing computer models with further observations of the star and orbiting debris,” Farihi said.
Mars becomes the second planet after Earth that we know is wobbling around its axis. As to why — we’re yet unsure.
As the Red Planet spins during its day, it also wobbles and bobbles gently around its own axis, a new paper reports. Astronomers have no idea why this is happening, but the fact that Mars is the second planet we know of to do this (after Earth) could help us understand it better.
The Chandler wobble
This type of motion — a planet’s wobble around its own axis as it spins — is known as the Chandler wobble. Earth shows some 30 feet (9 meters) of amplitude in this wobble: its poles move in a circle with a 9-meter diameter around its axis, with a period of around 430 days.
Mars seems to be doing the same, albeit the diameter it spins on is way smaller: 4 inches (10 centimeters) off-center, with a period of around 200 days, according to Eos.org, the news blog of the American Geophysical Union (AGU).
The Chandler wobble is produced when a rotating body’s mass isn’t distributed evenly. Things like differences in density throughout its body or in its shape will lead to such a wobble. In Earth’s case, it is caused by its shape, which isn’t perfectly round. Although Earth’s is much more pronounced than that of Mars, it’s possible that the source of the wobble is the same for both planets.
Still, here’s where the mystery begins. Over time, we know that this wobble should fade out. It’s been calculated that for Earth, any Chandler wobbling should disappear within a century of it starting. However, we know that this isn’t the case — Earth has been wobbling for much longer than that.
Given that our planet is both geologically and biologically active, our running assumption so far is that shifts in atmospheric and ocean pressures (i.e. the movement of large bodies of water and gas) are constantly fueling this wobble, which is why it didn’t die out when our calculations said it would.
But Mars is neither geologically nor biologically active, as far as we know. It has no oceans and only a thin coating of an atmosphere. And yet it wobbles.
The movement was detected using 18 years’ worth of data collected by satellites around Mars: Mars Odyssey, Mars Reconnaissance Orbiter and, Mars Global Surveyor. Crunching the math leads to the same conclusion as it does on Earth: this wobble should end naturally, but so far, it hasn’t.
Our only guess so far is that, in Mars’ case, the Chandler wobble is fueled by atmospheric motions alone; this would fit with the much lower amplitude of motion compared to Earth’s own wobble. However, more data is needed before we can be certain.
However, we do know one thing for sure: if we’ve found two planets which wobble, we’re likely to see more in the future doing the same. Maybe we can understand what’s happening before we run into the third.
Water might be a byproduct of the formation of all rocky planets, a new study proposes.
From all we know of life today, water seems to be a key ingredient. Life on our planet spawned and lived its early years in water. So our efforts to find extraterrestrial life focused heavily on identifying planets with liquid water. However, a new study suggests that water may be much more bountiful in the universe than we’d expect. In fact, it may be a byproduct of the formation of any rocky planet.
“There are two hypotheses about the emergence of water. One is that it arrives on planets by accident, when asteroids containing water collide with the planet in question,” says Professor Martin Bizzarro from the Centre for Star and Planet Formation at the Faculty of Health and Medical Sciences, University of Copenhagen.
“The other hypothesis is that water emerges in connection with the formation of the planet. Our study suggests that this hypothesis is correct, and if that is true, it is extremely exciting, because it means that the presence of water is a byproduct of the planet formation process”.
Together with Assistant Professor Zhengbin Deng, Bizzarro performed an analysis of a black meteorite known as “Black Beauty”. This meteorite is 4.45 billion years old and found its way to Earth from the original crust of Mars. As such, it contains unique insight into the ancient history of the solar system. They explain that the findings showcase that water may be much more common in the universe than we’ve assumed up to now.
The duo found that Mars harbored water for the first 90 million years of its existence. This would be long before the planets in the inner Solar System (like Earth and Mars) were bombarded by water-rich asteroids, as per our previous hypothesis. In other words, it couldn’t have been asteroids seeding water onto planets (or, at least onto Mars).
Black Beauty was first discovered in the Moroccan desert, and soon found its way to the market — for around USD 10,000 dollars per gram. The team gathered the funds to buy some 50 grams of the meteorite back in 2017 and started working on it in the lab. They crushed and dissolved some 15 grams of the meteorite and processed them with a new technique they developed.
“We have developed a new technique that tells us that Mars in its infancy suffered one or more severe asteroid impacts. The impact, Black Beauty reveals, created kinetic energy that released a lot of oxygen. And the only mechanism that could likely have caused the release of such large amounts of oxygen is the presence of water,” Zhengbin Deng says.
“It suggests that water emerged with the formation of Mars. And it tells us that water may be naturally occurring on planets and does not require an external source like water-rich asteroids,” Bizzaro adds.
The dry river and lake beds visible on Mars today are undeniable proof that the planet once harbored liquid water. However, its surface is quite cold — so the authors wanted to understand how this could be. Their analysis suggests that asteroid impacts likely released a lot of greenhouse gases into its atmosphere. Their warming effect on the planet’s climate led to the conditions that allow for liquid water to exist on its surface.
Going forward, the team plans to examine microscopic water-bearing minerals in the asteroid, which have remained unchanged since they first formed.
The paper “Early oxidation of the martian crust triggered by impacts” has been published in the journal Science Advances.
We’ve found a lot of planets in recent years. Big and small, far and close, but they all have one thing in common: they’re in our galaxy. Now, a team of researchers from the US and China believe they’ve found the first planet outside of our galaxy, and it’s glorious.
Galaxies are big. Our galaxy is thought to host more than 100 billion stars, and measure about 100,000 light-years across. In other words, it would take a beam of light 100,000 years to cross the galaxy, and the fastest shuttle we’ve ever built only hit a peak speed of about 3% the speed of light.
But even this is just peanuts to space. Our neighboring Andromeda galaxy, for example, is over two times bigger than the Milky Way, and the biggest galaxy we know of (IC 1101) is 50 times the Milky Way’s size and about 2,000 times more massive.
The new planet candidate lies a whopping 23 million light years away, in the M51 Whirlpool Galaxy, relatively close to Ursa Major. Normally, it wouldn’t really be possible to identify a planet this far away, but researchers took advantage of a rare set of circumstances.
The object lies in a binary system that has a either black hole or a massive neutron star at the center (we don’t know for sure, but it’s very massive). This object is sucking on a nearby star, and in the process, emitting a huge X-ray signal which caught the attention of astronomers. X-ray signals of this nature are rare on the night sky, so it made for an interesting observation. The X-ray signal also happens to be very small — so small that even a relatively small object passing in front of it would temporarily block it, and this is exactly what researchers have observed.
“It is the first candidate for a planet in an external galaxy,” researchers note in the study. If it is confirmed, the planet would be called M 51-ULS1.
Simply put, there seems to be a planet passing in between this X-ray source and the Earth, creating an eclipse-type phenomenon. Researchers aren’t exactly sure that it is a planet since it’s too far to observe it directly, but they’ve ruled out all likely possibilities.
It will be a while before we can confirm this finding, but for now, it’s safe to say that out of the thousands of planet candidates we’ve found, we also have one outside our galaxy — and that’s pretty awesome in itself.
Journal Reference: M51-ULS-1b: The First Candidate for a Planet in an External Galaxy, arXiv:2009.08987 [astro-ph.HE] arxiv.org/abs/2009.08987
Every new exoplanet discovery is remarkable in its own way, and if that planet happens to be Earth-sized, it’s even more special. If it’s connected to a famous constant (Pi), it’s basically an astronomy party.
Pi, the ratio of a circle’s circumference to its diameter, isn’t exactly 3.14. In fact, it’s 3.141592653589793238… and goes on forever. But for most people, 3.14 is a good enough approximation — and for the astronomers looking for this new planet, the similarity was too striking.
“The planet moves like clockwork,” says Prajwal Niraula, a graduate student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), who is the lead author of a paper published today in the Astronomical Journal, titled: “π Earth: a 3.14-day Earth-sized Planet from K2’s Kitchen Served Warm by the SPECULOOS Team.”
“Everyone needs a bit of fun these days,” says co-author Julien de Wit, of both the paper title and the discovery of the pi planet itself.
The planet is called K2-315b but already, astronomers have nicknamed it π Earth. It’s the 315th planetary system discovered with data from K2, the successor of the Kepler telescope — just one shy from another coincidence that would have made it number 314.
The first signs of the planet were reported in 2017, but it was only confirmed more recently. π Earth has approximately 95% of Earth’s mass, making it essentially Earth-sized, and orbits a star that’s 5 times smaller than the Sun.
However, there’s virtually no chance of life as we know it on the planet. For starters, the planet orbits very close to its star, and astronomers estimate that it heats up to around 450 Kelvin (177 degrees Celsius, or 350 degrees Fahrenheit). As mentioned, the planet also circles its star every 3.14 days — so a ‘year’ on the planet is little more than three days, which means it moves at a blistering speed of 81 kilometers per second, or about 181,000 miles per hour (compared to 30 km/s at the Earth’s equator).
However, the planet is interesting in itself, more than being a mathematical curiosity.
“This would be too hot to be habitable in the common understanding of the phrase,” says Niraula, who adds that the excitement around this particular planet, aside from its associations with the mathematical constant pi, is that it may prove a promising candidate for studying the characteristics of its atmosphere.
“We now know we can mine and extract planets from archival data, and hopefully there will be no planets left behind, especially these really important ones that have a high impact,” says de Wit, who is an assistant professor in EAPS, and a member of MIT’s Kavli Institute for Astrophysics and Space Research.
The researchers are also interested in a follow-up study on the Pi planet with the upcoming James Webb Space Telescope (JWST), to see potential details of the planet’s atmosphere. For now, they are combing through other telescope datasets for signs of Earth-like planets — Pi or non-Pi.
When it comes to the surface temperature of planets, distance to the Sun is the main factor, but it’s not the only one. Turns out, the atmosphere (and in some cases geological processes) can have a major impact.
This is why the hottest planet in the solar system isn’t Mercury (the closest to the Sun), but Venus — and the reason has to do with something we’re very familiar with: carbon dioxide.
A familiar culprit: greenhouse gas
Venus, named after the Roman goddess of Love (Aphrodite for the Greeks), is not exactly an inviting place. Its scorching surface can reach 880°F (471°C), and if that doesn’t scare you, Venus is riddled with active volcanoes and hot, toxic sulfur fumes.
It’s no surprise that Venus is hot since it’s much closer to the Sun than the Earth. Venus lies 108.93 million km away from the Sun, 30% closer than the Earth. But why is Venus hotter than Mercury, which lies only 59.187 million km from the Sun?
The answer lies in the Venusian atmosphere.
The atmospheric pressure on Venus is 92 times stronger than that of Earth — it would feel like being 900 m (3,000 ft) underwater. This thick atmosphere wraps the planet like a blanket, and to make matters even hotter, the atmosphere is 96% carbon dioxide — which, as you’re probably aware, is an important greenhouse gas and a driver of rising temperatures. In other words, Venus has a runaway greenhouse gas problem that traps heat in the atmosphere.
Meanwhile, Mercury has a very thin atmosphere. Much of the heat that Mercury receives from the sun is quickly lost back into space, whereas heat on Venus doesn’t escape.
It’s a never-ending cycle of heat being trapped inside by carbon dioxide and releasing more carbon dioxide. This is what happens when an atmosphere absorbs too much carbon dioxide: the heat has nowhere to go and it triggers a self-enforcing feedback loop.
This becomes even more obvious when we look at the difference between the maximum temperature and the average temperature.
The day is longer than the year
Both Mercury and Venus rotate very slowly; on Venus, a day lasts 243 Earth days, while a year lasts 225 Earth days — the Venusian day is longer than the year.
Because they rotate so slowly, you’d expect the planets to have massive temperature differences between the sunny side and the dark side — and that’s exactly what we see on Mercury. There’s a huge, over 1000 °F difference between day and night. But for Venus, that’s not really the case.
Because Venus has such a thick and greenhouse-potent atmosphere, the temperature is relatively constant on the entire planet. While the hottest temperature on Mercury is close to that of Venus, if we we were to take an average, it wouldn’t even be close.
Planet / Satellite
Minimum surface Temperature
Maximum Surface Temperature
-275 °F (- 170°C)
840 °F (449°C)
870 °F (465°C)
870 °F (465°C)
– 129 °F (- 89°C)
136 °F (58°C)
– 280 °F (- 173°C)
260 °F (127°C)
– 195 °F (- 125°C)
70 °F (20°C)
If Venus didn’t have the atmosphere it does, its night temperature would also be much lower, like Mercury’s — and the average temperature would also be lower than Mercury’s.
Another consequence of this atmosphere is that there’s no ice on Venus, which is hardly surprising given the average temperature. While on Mercury, ice can find shelter in the polar, always-shaded impact craters where temperatures are below freezing. NASA’s MESSENGER mission detected evidence of water ice at both of Mercury’s poles, probably delivered by comet impacts.
Meanwhile, the surface of Venus is extremely dry.
It’s not always clear if the planet was always like this. During its early evolution, Venus likely had liquid water on its surface, but it was ultimately evaporated by ultraviolet rays from the Sun. If, through some magical experiment, you were to create some water on Venus, it would boil away almost immediately. Yet despite all these differences, Venus was once considered Earth’s twin.
The reason for this is mostly regarding the planet’s size and mass. Venus and Earth, two neighboring planets, are very similar in some regards: Earth has a mean radius of 6,371 km, while Venus has a radius of about 6,052 km. Meanwhile, the mass of the Earth is 5,972,370,000 quadrillion kg, compared to 4,867,500,000 quadrillion kg for Venus. So essentially, Venus is 0.9499 the size of Earth and 0.815 the mass. It also has an atmosphere… and that’s pretty much where the similarities end.
Around 60% of Venus is covered by flat, smooth plains, marred by thousands of active volcanoes, ranging from 0.5 to 150 miles (0.8 to 240 km) wide. Venus features long, winding canals that run for more than 3,000 miles (5,000 km) — longer than any other planet.
The temperature is ungodly, as we’ve already mentioned, the atmosphere is thick and heavy, permanently covered in clouds. Most man-made materials would melt rapidly on Venus, and a human mission to Venus is nothing more than a pipe dream at this point.
Venus also rotates in the opposite direction than the Earth, and as we mentioned previously, it rotates very slowly.
If Venus is Earth’s twin, it can only qualify as its evil twin.
How we study Venus
Up until the 1960s, there was rich speculation that Venus may harbor life forms — but all that dwindled quickly when spacecraft actually started studying Venus.
Studying Venus is no easy feat. In fact, Venus is so inhospitable that many scientists were skeptical that a mission would even be possible. The Soviets sent a few missions to Venus, but the first ones all failed.
Mariner 2 was the first spacecraft to visit Venus in 1962. Eventually, in 1981, the Venera 13 mission finally managed to make it through the hot layers of the atmosphere and land on the surface. It managed to survive for 127 minutes, during which it sent color photos and measurements to Earth.
Then, transmission stopped and Venera 13 melted.
In 1990, the US spacecraft Magellan used radars to map the Venusian surface — an extremely important step, since Venus is always shrouded by sulfur layers that make it impossible for visible light to pass. Magellan mapped 98% of the surface with a resolution of approximately 100 meters and are still the most detailed maps we have of Venus. In more recent times, interest in Venus has decreased and recent missions have only been flybys, taking snapshots of Venus en route to other destinations. The Japanese mission Akatsuki, plagued by problems, is currently studying Venus’ atmosphere.
Understanding the atmosphere and atmospheric processes on Venus could help us better understand some of the atmospheric phenomena we see here on Earth.
Venus’ runaway greenhouse effect could show us how the Earth might look in the future if we don’t take climate change seriously. It’s an important lesson on what can happen when a planet has a high carbon dioxide level in the atmosphere. According to recent studies, Venus may have had a liquid ocean and a habitable surface for up to 2 billion years of its early history — an important cautionary tale.
Lastly, although Venus is hellish and inhospitable, some researchers still believe that extremophiles (organisms adapted to extreme conditions) could still survive on Venus. In 2019, researchers proposed that an unexplained absorption phenomenon could be explained by colonies of microbes in the atmosphere on Venus. While far from being a promising place to look for life, it’s still intriguing enough to study.
Venus studies have been great lessons, enabling researchers to better understand other rocky planets, as well as the Earth.
It’s a hot, hellish place — the hottest planet in the solar system. But we can still learn from it.
The gas planets, the giants of the solar system, the jovian planets — call them what you will, these planets have fascinated mankind for centuries, and they’re still one of the more intriguing astronomical bodies out there.
Jovian literally means “Jupiter-like”, from “Jove” — another name for the Roman god Jupiter (called Zeus by the Greeks). They are primarily composed of gas or ice and are much larger than the Earth. They’re also much easier to detect than other planets — largely because they’re so big.
You can’t walk on a jovian planet
Jovian planets are comprised of fluid (gases or ices) rather than rock or other solid matter. Although giant rocky planets can exist, these are thought to be much rarer than gas or ice giants.
Jupiter is made up almost entirely of hydrogen and helium — the same elements found in the Sun, though at different temperatures and pressures. Here on Earth, hydrogen and helium are gases, but under the huge temperatures and pressures of Jupiter, hydrogen can be a liquid or even a kind of metal. We’re not entirely sure what lies at the center of Jupiter, but researchers believe that most likely, the core is similar to a thick, boiling-hot soup with a temperature of about 55,000 Fahrenheit (30,000 Celsius).
Saturn has a similar structure, with layers of metallic hydrogen, liquid hydrogen, and gaseous hydrogen, covered by a layer of visible clouds. Unlike Jupiter and Saturn, Uranus and Neptune have cores of rock and metal and different chemical compositions.
We’re not sure exactly what the surface of jovian planets is like, but based on all we know, it’s not something you can walk on. Jovian planets tend to have very thick clouds (the clouds on Jupiter, for instance, are 30 miles or 50 km thick). After that, there’s gaseous hydrogen and helium, then more and more condensed gas, until you ultimately end up in liquid, metallic hydrogen. Saturn has a similar structure, though it is far less massive than Jupiter.
You might even have trouble realizing where the atmosphere ends and where the “planet” begins.
Uranus and Neptune, much smaller than both Jupiter and Saturn, have gaseous hydrogen surrounding a mantle of ice and a rocky core.
Jovian planets also have atmospheres with bands of circulating material. These bands typically encircle the planet parallel to the equator, with lighter bands lying at higher altitudes and being areas of higher pressure, and darker bands being lower in the atmosphere as low-pressure regions. This atmospheric circulation is similar only in principle to that on Earth, it has a very different structure.
There are also other, smaller visible structures. The most famous of these is Jupiter’s Great Red Spot, which is essentially a giant storm that has been active for centuries. Saturn’s hexagon is another very well-known feature — both of these are much larger than the Earth itself.
These spinning balls of gas and liquids are truly impressive, and we’re still learning new things about them.
Jovian planets in our solar system
Not all gas planets are alike. In fact, the reason why some astronomers prefer the term jovian planets to gas giants is that not all jovian planets are made of gas.
For instance, just Jupiter and Saturn are true gas giants, whereas Uranus and Neptune are ice giants. However, even this is a bit misleading: at the temperature and pressures on these planets, distinct gas and liquid phases cease to exist. Even so, the chemistry of the two groups is different: hydrogen and helium dominate Jupiter and Saturn, whereas, in the case of Uranus and Neptune, it’s water, methane, and ammonia. The two latter planets are thought to have a slushie-like mantle that spans over half of the planet diameter.
All four of these planets have large systems of satellites, and these satellites can be very interesting in their own right (we’ll get to that in a minute — there’s a good chance that life may be hiding in the jovian satellites). Saturn, for instance, has 82 designated satellites, and countless undesignated moonlets. Despite being larger, Jupiter “only” has 79 known satellites. Uranus has 27 and Neptune has 14.
All these four planets also have rings, though Saturn’s are by far the most pronounced.
Much of what we know about gas and ice giants in general, we extrapolate from what we see in our own solar system. This being said, astronomers are aware that jovian planets can be very different and have a much greater variety than we see in our solar system.
Extrasolar Jovian planets
Roughly speaking, jovian planets can be split into 4 categories:
gas giants (like Jupiter and Saturn) — mostly consisting of hydrogen and helium, and only 3-13% heavier elements;
ice giants (like Neptune and Uranus) — a hydrogen-rich atmosphere covering an icy layer of water;
massive solid planets (somewhat similar to the Earth, but huge) — tangible evidence for this type of planet only emerged in 2014, and these planets are still poorly understood. Astronomers suspect that solid planets up to thousands of Earth masses may be able to form, but only around massive stars;
super puffs — planets comparable in size with Jupiter, but in mass with the Earth. These planets are super rarefied, and were only discovered in the past decade; the most extreme examples known are the three planets around Kepler-51.
Based on what we’ve seen so far, jovian planets seem pretty common across our galaxy. However, we’ve only started discovering exoplanets very recently, and it’s hard to say whether the planets we’ve found so far are representative of the larger picture.
However, based on the fact that researchers have discovered far more Neptune-sized planets than Jupiter-sized planets (although the latter are easier to discover), it’s pretty safe to say that it’s the Neptune-sized planets that are more common.
A particularly interesting class of jovian planets is the so-called Hot Jupiters.
Hot Jupiters are the easiest planets to detect. As the name implies, they are Jupiter-sized planets, but they lie very close to their stars and have a rapid orbital period that produces effects that are more easily detected. For instance, one such planet revolved around its star in only 18 hours, making for one very short year. Another freakish example of a Hot Jupiter is believed to have surface temperatures of 4,300°C (7,800°F) — which is hotter than some stars we know.
Extrasolar planets, and Hot Jupiters in particular, can shed a lot of light on the evolution of solar systems. It is believed that these planets form in the outer parts of solar systems (like Jupiter), but they slowly migrate towards the star, drawn by gravitational attraction. As they do so, they could wreak havoc on the entire solar system, much like a big billiards ball.
Some jovian planets get so large that they blur the line between a planet and a brown dwarf. Brown dwarfs are neither truly stars nor planets. As a rule of thumb, jovian planets are only “planets” until they are 15 times the mass of Jupiter — after that, they “become” brown dwarfs.
Because of the limited techniques currently available to detect and study exoplanets, there are still many things we don’t know about exoplanets, even those as big as Jupiter. We tend to associate these planets by size with the ones in our own solar system, piecing together other available information (which is scarce). As our telescopes, equipment, and theoretical models become better, we will no doubt better our understanding of jovian planets, and exoplanets in general.
Life around Jovian planets
Jovian planets are not exactly life-friendly — at least not directly. A giant, spinning, mass of fluid you can’t even stand on, either very hot or very cold, doesn’t sound very attractive to life forms. But jovian satellites are a different story. In fact, astronomers are starting to believe that the satellites of Jupiter and Saturn may be the best places to look for extraterrestrial life in our solar system.
Both Jupiter and Saturn lie rather far from the Sun. They are cold, frigid places, as are their satellites — at least on the surface.
Researchers now believe that some of the icy satellites of Jupiter and Saturn (especially Europa and Enceladus) could host life under their frozen surfaces.
Although the surface temperatures are extremely low on these satellites, astronomers have some clues that both satellites may harbor oceans of liquid water beneath the frozen surface. Basically, the huge gravitational effect from their host planets causes friction and shear in the ice, which produces sufficient heat to melt the ice. This is called tidal heating. Geothermal and geological activity may also contribute to this effect, creating a liquid, salty water beneath the ice — and while this has not yet been confirmed, these could be suitable conditions for life to emerge.
In addition to Europa and Enceladus, several other jovian satellites could harbor life (with various degrees of likelihood): Callisto, Ganymede, Io, Triton, Dione, and even Pluto’s moon Charon could all have a liquid ocean compatible with life. NASA’s Clipper mission is set for launch in 2024, with the goal of exploring Europa’s potential habitability. Some scientists believe there are as many habitable exomoons as there are habitable exoplanets.
Jovian planets seem to play a key role in the structure of solar systems. Whether their satellites can hold life or not, they are an extremely important puzzle piece in our understanding of how solar systems form, evolve, and how the Earth fits in this grand cosmic puzzle.
The term was first used in 2006 to describe celestial bodies that were comparable in size to Pluto. Since then it has taken on a broader usage, with the IAU (International Astronomers’ Union) currently recognizing five bodies in the Solar System as being dwarf planets — and an extra six more await a decision.
However, since its addition to the old classification system (which held that nine planets were orbiting the Sun), the term ‘dwarf planet’ has caused quite a lot of confusion (and controversy). So let’s see what it’s meant to represent and whether Pluto does actually deserve to be called as such.
A dwarf planet is “(a) in orbit around the Sun [or another star], (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite,” according to the IAU’s RESOLUTION B5 on the Definition of a Planet in the Solar System.
In essence, that definition says that dwarf planets are objects in stable orbit around a star that are massive enough to maintain a round shape but not massive enough to clear all other material out of their orbit, and that they don’t orbit another planet.
It’s basically these last two points that differentiate a dwarf planet from a regular one and from moons. Full-blown planets always clear their orbits, according to the current definition, but neither they nor dwarf planets can orbit another planet — only moons do that.
There are currently five dwarf planets recognized as such by the IAU in the Solar System: Pluto, Ceres, Eris, Makemake, and Haumea. There is still some debate whether Eris, Makemake, or Haumea fit the bill, however, as our observations of these bodies are still far from perfect. Other nearby contenders include Orcus, 2002 MS4, Salacia, Quaoar, 2007 OR10, and Sedna; the IAU further decided that Trans-Neptunian Objects (TNOs) with an absolute magnitude higher than +1 and a diameter of 838 km or more are to be considered dwarf planets until more data can be gathered on their nature.
On the matter of shape
The roundedness criteria is actually pretty central in how we think about planets. Roundedness in the case of stellar objects is largely the product of gravity. Planets become round (sorry, Flat Earthers) when their gravity becomes strong enough to plastically deform their surfaces and to overpower all other forces affecting them. Strong gravity is necessary to impart a rounded shape to a planet by flattening high-elevation areas and filling in low-lying ones.
It’s a pretty reliable indicator of planethood, all things considered. Asteroids or comets are small and don’t have the mass to round themselves out; their final shape is the product of outside forces acting on the body. Centrifugal forces generated by rotation, friction, impacts, or the tidal pull of other bodies are what create their irregular shapes.
Those bodies for which gravity is a significant but not dominant factor morph into spheroid (sphere-like) shapes. This is a bit of a middle-ground between the shape gravity works towards and the irregular mess promoted by outside forces.
An object with high gravity will come as close to a perfect sphere as possible, reaching ‘hydrostatic equilibrium‘. To illustrate, the Earth isn’t perfectly round — it’s an oblate spheroid. This is due to the planet’s rotation around its own axis, which generates centrifugal forces that pull on the equator, making the Earth look a bit like a sphere you pressed down on. The faster a body rotates, the more deformation it will experience around its equator. The dwarf planet Haumea, for example, is almost twice as long at its equator as it is at the poles.
Tidal forces are the gravitational pull of other planets and/or celestial bodies on an object. This helps deform it (on Earth we see this as the waxing and waning of the tide) and can tidally-lock an object in relation to another. The moon is tidally locked to Earth; no matter when you look at it, it’s always showing the same hemisphere.
The IAU’s definition uses shape instead of mass because particularities of a given celestial body, such as its chemical composition, also have a part to play in their overall shape. Mass alone isn’t a reliable indicator of a body’s overall characteristics. Water ice, for example, is much more easily deformed by gravity than a chunk of solid rock.
On the matter of its neighborhood
A celestial body’s ability to remove all smaller ones along its orbit is also known as ‘orbital dominance’. Planets have virtually complete orbital dominance through collision, capture, or other interaction with other space-born bodies they come into contact with; dwarf planets do not.
Orbital dominance once again ties into a body’s mass, which dictates its gravitational force (do keep in mind that gravitational pull is inversely proportional to the squared distance between two bodies).
An easy way to think about this factor is that planets have enough mass to ‘overpower’ all other bodies of similar size in the volume of space they transit. Dwarf planets, being smaller, need to share their space with other chunks of matter.
This is the most contentious point in the definition. For one, an argument can be made that a planet’s orbit is never fully cleared as objects come and go through space. Secondly, there’s also the question of how can we reliably say that a planet did in fact clear its orbital neighborhood; and also, for that matter, where does a planet’s neighborhood end? The IAU doesn’t put any actual figures on its definition of dwarf planets. The definition can thus be seen as more of a theoretical guideline than a hard criterion; it has drawn criticism for this fact.
“In no other branch of science am I familiar with something that absurd,” said New Horizons principal investigator Alan Stern for Space.com in 2011. “A river is a river, independent of whether there are other rivers nearby.”
“In science, we call things what they are based on their attributes, not what they’re next to.”
Stern says that Earth, Mars, Jupiter, and Neptune have not fully cleared their orbital zones either, but we still call them planets. Some 10,000 near-Earth asteroids orbit the Sun alongside our planet, he explains. Jupiter drags some 100,000 Trojan asteroids on its way through space, Stern adds. The main criticism leveled at his approach is that these planets completely control the other asteroids and bodies within their orbit via gravitational pull.
The debate is especially heated because Pluto’s status as a planet hinges on this particular point of the IAU’s definition. Pluto is gravitationally dominated by Neptune, which constrains its orbit. It also has to share its neighborhood with several objects in the Kuiper belt of similar size, effectively dooming it to a dwarf planet status under the current definition.
It’s also relevant for exoplanets. Our current equipment and techniques can’t directly determine whether a planet very far away has cleared its orbit. Here, however, the IAU has taken some steps to clarify matters: it established a separate working definition for extrasolar planets in 2001, and decided that the minimum size and mass requirements for planets in the Solar System apply to exoplanets as well.
“As new claims are made in the future, the WGESP [Working Group on Extrasolar Planets] will weigh their individual merits and circumstances and will try to fit the new objects into the WGESP definition of a “planet”, revising this definition as necessary,” the statement reads.
“This is a gradualist approach with an evolving definition, guided by the observations that will decide all in the end.”
The main current issues with the IAU’s classification system is that while it’s easy to understand, it doesn’t really withstand impact with reality on the ground. Space is a big place and it doesn’t abide by simple rules you can fit in a four-point list.
However, we’re still in a very early stage of space exploration. The exact difference between planets, dwarf planets, and moons is pretty inconsequential to our lives, even if it does rile up the spirits. As our reach into space extends, such classifications will become more important. But our ability to clearly define the multitude of shapes, sizes, and types of matter we’ll find in space will also be much better by then.
The European Space Observatory’s SPHERE instrument has spotted what may be the smallest small planet in our solar system.
The object christened Hygiea is currently considered an asteroid — but it might be classified as a dwarf planet. It’s the fourth largest body in the asteroid belt after Ceres, Vesta, and Pallas. The reclassification follows on the heels of new observations: for the first time, astronomers were able to look at Hygiea with a sufficiently-high resolution to study its surface and to determine that it is spherical (a condition necessary to be considered a planet).
Hygiea might thus officially become the smallest dwarf planet in our solar system — a title currently held by Ceres,
Small but significant
“Thanks to the unique capability of the SPHERE instrument on the VLT (Very Large Telescope), which is one of the most powerful imaging systems in the world, we could resolve Hygiea’s shape, which turns out to be nearly spherical,” says lead researcher Pierre Vernazza from the Laboratoire d’Astrophysique de Marseille in France.
“Thanks to these images, Hygiea may be reclassified as a dwarf planet, so far the smallest in the Solar System.”
Prior to this discovery, we already knew that Hygiea satisfied three of the four requirements to be considered a dwarf planet: it orbits around the Sun, it is not a moon, and it has not cleared the neighborhood around its orbit (like a proper planet would). The final requirement is for it to have enough gravitational force to pull itself into a roughly spherical shape. Thanks to new observations, we now know that Hygiea passes this criterion as well.
Based on the SPHERE data, the team estimated Hygiea’s size to be around 430 km in diameter. Ceres is closer to 950 km in diameter while Pluto, the largest dwarf planet, comes close to 2400 km.
One surprising find was that Hygiea lacks any large impact craters on its surface. The team really expected to find such a structure on its surface as Hygiea is the main member of one of the largest asteroid families (with around 7000 members) that all come from the same parent body. It was believed that Hygiea would have been left scarred by the event that led to that original body breaking apart. Although the astronomers observed Hygiea’s surface with a 95% coverage, they could only identify two relatively small craters.
“This result came as a real surprise as we were expecting the presence of a large impact basin, as is the case on Vesta,” says Vernazza.
“Neither of these two craters could have been caused by the impact that originated the Hygiea family of asteroids whose volume is comparable to that of a 100 km-sized object. They are too small,” explains study co-author Miroslav Bro of the Astronomical Institute of Charles University in Prague, Czech Republic.
Computer simulations suggest that Hygiea’s shape and the large number of members in its asteroid family were the result of a major head-on collision between the parent body and an object between 75 and 150 km in diameter around 2 billion years ago, The simulations showed that this violent impact completely shattered the parent body. Hygiea, the simulations suggest, is the product of left-over pieces that reassembled themselves into a round shape surrounded by companion asteroids.
“Such a collision between two large bodies in the asteroid belt is unique in the last 3-4 billion years,” says Pavel Ševeček, a PhD student at the Astronomical Institute of Charles University and paper co-author.
“Thanks to the VLT and the new generation adaptive-optics instrument SPHERE, we are now imaging main belt asteroids with unprecedented resolution, closing the gap between Earth-based and interplanetary mission observations,” Vernazza concludes.
The paper “A basin-free spherical shape as outcome of a giant impact on asteroid Hygiea” has been published in the journal Nature Astronomy.
Planets come in all sha… planets come in various sizes. But, some of the most striking characteristics that set them apart are their physical and chemical particularities, which we use to categorize the myriad of planets we’ve found in space.
I like planets. I like them so much I live on one. They’re heavy enough for gravity to make them round, their orbits are clear of debris, and they don’t burn like stars do. But, there’s a lot of variation in what they are and the experience they offer.
So, today, I’d thought it would be exciting to look at all the different types of planets — some of which we’ve seen in the great expanse of space, some of which we’re only expecting to find. In no particular order, they are:
A star is a delicate system where gravity compresses and heats everything up while the nuclear fusion at their core pushes outwards. With too much pressure, electrons can’t move freely, so the reaction stops. With too much ‘boom’, there’s not enough pressure to keep the reaction going.
Teetering on the edge of starhood, brown dwarfs have outgrown any definition of a ‘planet’. Yet, they’re just not quite a star. Ranging from 13 to 80 times the mass of Jupiter, brown dwarfs are immense embers barreling through space, fusing deuterium and lithium to keep themselves slightly alight. However, they need yet more matter to be able to fight their own gravity, so they can’t ignite.
Brown dwarfs aren’t planets. They don’t form like planets — they form like stars. Instead of material slowly clumping together, brown dwarfs are born from clouds of gas collapsing in on themselves.
The chonk de la chonk, gas giants are the largest planets to ever dot the universe. They are composed primarily (>90%) of hydrogen and helium (the two simplest elements in the periodic table) with traces of other compounds thrown in for good measure. Hydrogen and helium give these planets an overall brown-yellow-ocher palette, with water and ammonia clouds peppering their highest layers white. Owing to the nature of their bodies, these giants are blanketed by wild storms and furious winds.
We don’t know much about their cores, only that it has to be immensely hot (around 20,000 Kelvin, K) and pressurized in there. The main hypotheses hold that gas giants either have molten rocky cores surrounded by roiling oceans of gas, diamond cores, or ones made of super-pressured (metallic) hydrogen nuggets.
They are sometimes called ‘failed stars’ because hydrogen and helium keep stars running, but gas giants don’t have enough mass to spark nuclear fusion. We have two of them in the solar system, Jupiter and Saturn.
Most exoplanets we’ve found so far are gas giants — just because they’re huge and easier to spot.
Very similar to gas giants but won’t return your texts. Ice giants are believed to swap out hydrogen and helium (under 10% by weight) in favor of oxygen, carbon, nitrogen, and sulfur, which are heavier. Boiled down, we don’t really know what elements these planets are made of — their (admittedly thin) hydrogen envelopes hide the interior of the planets, so we can’t just go and check. This outer layer is believed to closely resemble the nature of gas giants.
Still, it is believed that, while not entirely made of the ice we know and love here on Earth exactly, there is water and water ice in their make-up. They get their name from the fact that most of their constituent matter was solid as the planets were forming, and because planetary scientists refer to elements with freezing points above about 100 K (such as water, ammonia, or methane) as “ices”.
Ice giants are, as per their name, quite gigantic, but they tend to be smaller than gas giants. However, owing to their much-denser make-up, they are also more massive overall. There are two ice giants in our solar system, Uranus and Neptune. Water, in the form of a supercritical ocean beneath their clouds, is believed to account for roughly two-thirds of their total mass.
Both ice giants and gas giants have primary atmospheres. The gas they’re made from was accreted (captured) as the planets were forming.
Also known as terrestrial or telluric planets (from the Latin word for Earth), they are formed primarily of rock and metal. Their main feature is that they have a solid surface. Mercury, Venus, Earth, and Mars, the first four from the Sun, are the rocky planets of our solar system.
To the best of our knowledge rocky planets are formed around a metallic core, although the hypothesis of coreless planets has been floated around.
Atmospheres, if they have one, are secondary — formed from captured comets or created via volcanic or biological activity. Rocky planets also form primary atmospheres but fail to retain them. Secondary atmospheres are much thinner and more pleasant than those of Saturn or Uranus. That’s not to say a secondary atmosphere can’t influence its planet: Venus’s rampant climate disaster is a great example.
Mercury, with a metallic core of 60–70% of its planetary mass, is as close as we’ve found to an Iron planet. Both those and the much more bling Carbon planets thus remain hypothetical. Another exciting and cool-named hypothetical class of rocky planets are Chthonians, the rock or metal cores of gas giants stripped bare.
Rocky worlds can harbor liquid water, terrain features, and potentially tectonic activity. Tectonically-active planets can also generate a magnetic field.
Such planets come in many different sizes. Earth is Earth-sized, Mercury is only about one third of it, while Kepler-10c is 2.35 times as large as our planet. Density is also a factor. Without going to a planet and studying its interior structure, it’s impossible to accurately estimate its density. As a rule of thumb, however, uncompressed density estimates for a rocky planet tend to be lower the farther away it orbits its star. It’s likely that planets closer to the star would thus have a higher metal (denser) content, while those further away would have higher silicate (lighter) content. Gliese 876 d is 7 to 9 times the mass of Earth.
The first extrasolar rocky planets were discovered in the early 1990s. Ironically, they were found orbiting a pulsar (PSR B1257+12), one of the most violent environments possible for a planet. Their estimated masses were 0.02, 4.3, and 3.9 times that of Earth’s.
These planets contain a large amount of water, either on the surface or subsurface. They’re an offshoot of the rocky planet, either covered in liquid water or an ice layer over liquid water. We don’t know very much about them or how many there are out there because we can’t yet spot liquid surface water, so we use atmosphere spectrometry as a proxy.
Earth is the only planet on which we’ve confirmed the existence of liquid water at the surface so far. And although water does cover around 71% of the Earth, it only makes up for 0.05% of its mass, so we’re not an Ocean planet. On these latter ones, waters are expected to run so deep that they would turn to (warm) ice even at high temperatures (due to the pressure).
This type of planet remains one of the likeliest to harbor extraterrestrial life.
Fan-favorite Pluto, along with Ceres, Haumea, Makemake, and Eris are the dwarf planets of our solar system. Dwarf planets kind of stride the line between planets and natural satellites. They’re large enough to hold their own stable shape, even to hold moons themselves, but not enough to clear their orbit of other material.
Not technically planets because they orbit another planet, moons are nevertheless telluric bodies that vary in size from ‘large asteroid’ to ‘larger than Mercury’. Titan, Saturn’s largest moon, has its own atmosphere.
There are six planets in the Solar System that sum up to 185 known natural satellites, while Pluto, Haumea, Makemake, and Eris also harbor their own moons.
These are the planets your parents warned you about.
Rogue planets deserve a mention on this list despite the fact that they don’t orbit a star. They are, for all intents and purposes, planets that orbit the galactic core after being ejected from the planetary system in which they formed. It is also possible that, somehow, they formed free of any stellar host. PSO J318.5−22 is one such planet.
Image credits NASA, ESA / A. Simon (Goddard Space Flight Center) and M.H. Wong (University of California, Berkeley)
The image was taken on June 27, 2019 and centers on the planet’s titanic Great Red Spot. It records Jupiter’s color palette, swirling clouds, and turbulent atmosphere in much higher quality than previously-available images. These elements provide an important glimpse into the processes unfurling in the gas giant’s atmosphere.
Ten year challenge photo
The image was taken in visible light as part of the Outer Planets Atmospheres Legacy program (OPAL). It was snapped with Hubble’s Wide Field Camera 3 when Jupiter was 400 million miles from Earth — near “opposition,” or almost directly opposite the Sun in the sky.
OPAL generates global views of the outer planets each year using the Hubble Telescope, which are meant to provide researchers with the data they need to track changes in their storm, wind, and cloud dynamics.
One of Jupiter’s most striking features is the Great Red Spot, around which the current image focuses. The Spot is a churning storm, rolling counterclockwise between two bands of clouds (above and below the Great Red Spot) which are moving in opposite directions. The red band to the northeast of the Great Red Spot contains clouds moving westward and around the north of the giant tempest. The white clouds to its southwest are moving eastward to the south of the spot. The swirling filaments seen around its outer edge are high-altitude clouds that are being pulled in and around the storm.
Jupiter’s bands are created by differences in the thickness and height of the ammonia ice clouds that blanket its surface, both properties dictated by local variations in atmospheric pressure. The more colorful bands and are generally ‘deeper’ clouds. Lighter bands rise higher and are thicker, generally, than the darker ones.
Winds between bands can reach speeds of up to 400 miles (644 kilometers) per hour. All of the bands seen in this image are corralled to the north and to the south by powerful, constant jet streams — these remain stable even as the bands change color on the other side of the planet. The band of deep red and bright white that border the Giant Red Spot also become much fainter on the other side of Jupiter.
You can learn more about how these colors formhere.
Artist impression of planetary fragment orbiting a white dwarf. Credit: University of Warwick/Mark Garlick.
Astronomers have discovered a planetary body orbiting a white dwarf — the remaining compact core of a deaf low-mass star. This discovery hints at what conditions Earth might encounter when the Sun begins to die, billions of years from now.
The observable universe is littered with white dwarf stars, however, this was one of the few rare occasions that scientists have discovered orbiting debris around such a star. The planetesimal, which lies 410 light-years from Earth in the constellation Virgo, is believed to be no larger than a couple of hundreds of miles in diameter.
When a star similar in size to the Sun runs out of fuel, it starts expanding greatly in size into a red giant. As it does so, its intense gravity is capable of ripping apart any closely orbiting planets. Astronomers think that this is what happened to the small rocky body that they’ve observed, which probably used to be a dense planet.
When our sun will go through the same process in about 5 billion years, it will obliterate everything inside Mars’ orbit and disrupt the orbit of planets further out. The survival of life on Earth under these conditions is out of the question and scientists are still debating whether our planet will physically survive or be devoured by the sun. These latest findings suggest a bleak outcome is very likely.
“The star would have originally been about two solar masses, but now the white dwarf is only 70% of the mass of our Sun. It is also very small – roughly the size of the Earth – and this makes the star, and in general all white dwarfs, extremely dense,” Manser said in a statement.
“The white dwarf’s gravity is so strong – about 100,000 times that of the Earth’s – that a typical asteroid will be ripped apart by gravitational forces if it passes too close to the white dwarf.”
In order to find the planetesimal, researchers led by University of Warwick astrophysicist Christopher Manser employed a method called spectroscopy, which involves analyzing the different wavelengths of light emitted by an object. With the help of the Gran Telescopio Canarias in La Palma, Spain, the team of astronomers detected changes in the color of light emitted by a disc around the white dwarf known as SDSS J122859.93+10432.9, orbiting with a period of two to three minutes. The disc has a comet-like tail and is mostly made of iron, nickel, and other metals. It is the second solid remnant of a planet to have ever been discovered orbiting a white dwarf.
“The general consensus is that 5-6 billion years from now, our Solar System will be a white dwarf in place of the Sun, orbited by Mars, Jupiter, Saturn, the outer planets, as well as asteroids and comets. Gravitational interactions are likely to happen in such remnants of planetary systems, meaning the bigger planets can easily nudge the smaller bodies onto an orbit that takes them close to the white dwarf, where they get shredded by its enormous gravity,” Manser said.
Other objects might still orbit the dying distant star. However, the white dwarf is so faint that astronomers are unable to see anything orbiting farther out with their current tools. In the future, Manswer and colleagues plan on using spectroscopy to discover other planetary fragments orbiting white dwarfs.
“Learning about the masses of asteroids, or planetary fragments that can reach a white dwarf can tell us something about the planets that we know must be further out in this system, but we currently have no way to detect,” Manser concluded.
If you’d ask most people what; the closest planet to Earth, you’d probably come across one answer: Venus. That answer, while apparently logical, is not really true. Mercury is the planet closest to us.
Even more surprising is the fact that Mercury is the closest neighbor, on average, to each of the other seven planets in the solar system. How can this be?
Image credits: Image: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington (Wikimedia Commons).
Mercury’s in retrograde
What’s the planet closest to the Earth? Even without any prior knowledge, a decent guess would be Venus or Mars — these are our planetary neighbors, after all. A simple Google search reveals that Venus’ orbit is closer to that of Earth’s so, naturally, Venus must be the answer, right?
Wrong. Mercury is the planet closest to Earth — at least on average.
As it turns out, Venus being the closest planet to Earth is simply a misconception — one that has propagated greatly through the years.
“By some phenomenon of carelessness, ambiguity, or groupthink, science popularisers have disseminated information based on a flawed assumption about the average distance between planets,” write engineers Tom Stockman, Gabriel Monroe, and Samuel Cordner in a commentary published in Physics Today.
Instead, they recommend a different method of measuring which planet is closest, which they demonstrated using the motions of the planets within the last 10,000 years.
“By using a more accurate method for estimating the average distance between two orbiting bodies, we find that this distance is proportional to the relative radius of the inner orbit.”
Using this method, Mercury is closer to Earth on average. A GIF created by Reddit user u/CharcoalCharts does a great job at depicting this (the Earth is in Blue). The Earth is usually closest to Mercury, although, at some points of the year, it’s closest to Venus or Mars.
It feels intuitive that the average distance between every point on two concentric ellipses is closer than ellipses which are farther apart, but this is not necessarily the case. While Venus can get very close to the Earth (at only 0.28 Astronomical Units, with 1 AU being the distance from the Earth to the Sun), the two planets can also be quite far apart, at 1.72 AU. In total, Venus is 1.14 AU from Earth, but Mercury is a much closer 1.04 AU.
There are also two other shocking conclusions from this: first of all, on average, the Sun is closest to the Earth than any other planet (because it’s at 1 AU by definition). Secondly, it’s not just the Earth — Mercury is the closest neighbor of all planets in the solar system. In other words, Uranus is, on average, closer to Mercury than its presumed neighbor, Neptune. The same stands for even the dwarf planet Pluto (we still love you, Pluto!).
A simulation of an Earth year’s worth of orbits by the terrestrial planets begins to reveal that Mercury (gray in orbital animation) has the smallest average distance from Earth (blue) and is most frequently Earth’s nearest neighbor. Image credits: Tom Stockman/Gabriel Monroe/Samuel Cordner.
The whirly-dirly corollary
Researchers also found that the distance between two orbiting bodies is at a minimum when the inner orbit is at a minimum — something which they call the “whirly-dirly corollary” — after an episode of the cartoon Rick and Morty.
The method might also be useful in estimating distances between other orbiting bodies such as satellites or extrasolar planets or stars. In the Physics Today commentary, the researchers explain:
“As best we can tell, no one has come up with a concept like PCM to compare orbits. With the right assumptions, PCM could possibly be used to get a quick estimate of the average distance between any set of orbiting bodies. Perhaps it can be useful for quickly estimating satellite communication relays, for which signal strength falls off with the square of distance. In any case, at least we know now that Venus is not our closest neighbor—and that Mercury is everybody’s.”
Jupiter and its shrunken Great Red Spot. Credit: Wikimedia Commons.
A new factor has been added to the debate on whether or not living organisms could exist on Jupiter. You probably know Jupiter is a Jovian planet, a giant formed primarily out of gases. So how could alien life be able to exist in an environment where most of the phases of matter are absent? The answer is simply found in the element of water.
Within the rotating, turbulent Great Red Spot, perhaps Jupiter’s most distinguishable characteristic, are water clouds. Many of the other clouds in this enormous perpetual storm are comprised of ammonia and/or sulfur. Life theoretically cannot be sustained in water vapor alone; it thrives in liquid water. But according to some researchers, the fact alone that water exists in any form on the planet is a good first step.
The Great Red Spot is still a planetary feature which stumps much of the scientific community today. As it has been observed for the past century and a half, the Great Red Spot has been noticeably shrinking. The discovery of water clouds may lead to a deeper understanding of the planet’s past, including whether or not it might have sustained life, as well as weather-related information.
Some scientists have pondered the possibility that, due to the hydrogen and helium content in its atmosphere, Jupiter could be a diamond-producing “factory.” They have further speculated that these diamonds could enter into a liquid state and a rainfall of liquid diamonds would be in the Jovian’s weather forecast.
Likewise, the presence of water clouds means that water rain (a liquid) is not entirely impossible. Máté Ádámkovics, an astrophysicist at Clemson University in South Carolina, had this to say on the matter:
“…where there’s the potential for liquid water, the possibility of life cannot be completely ruled out. So, though it appears very unlikely, life on Jupiter is not beyond the range of our imaginations.”
Scientists are acting accordingly, researching the part which water plays in the atmosphere and other natural systems on Jupiter. They remain skeptical but eager to follow up on the new discovery. They shall also strive to find out just how much water the planet really holds.
Global LORRI mosaic of Pluto in true colour. Credit: NASA.
In 2006, the International Astronomical Union (IAU) set forth a new set of guidelines for what constitutes a planet. In a decision that surprised and even infuriated a lot of people, the commission announced that Pluto could no longer be considered a planet, in light of these new guidelines — and, ever since, the scientific community has debated Pluto’s place and status in the solar system.
If it looks like a planet, moves like a planet, then it’s a…
According to a new study, the IAU definition for a planet does not make much sense because astronomers have not used it in their work when discussing planets.
The IAU has been responsible for the naming and nomenclature of planetary bodies and their satellites since the early 1900s. Right at the end of the 2006 Prague General Assembly, members voted that the definition of a planet in the Solar System would be as follows:
A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighborhood around its orbit.
Pluto orbits the sun in a super-crowded region called the Kuiper Belt, which is jam-packed with asteroids, debris, and other so-called trans-Neptunian objects (TNOs) such as Eris or Sedna. Because it doesn’t clear its orbit, the IAU considered that Pluto didn’t fit criterion (c) and demoted to it to a ‘dwarf planet’ — objects that only meet the first two criteria.
Philip Metzger, a planetary scientist at the University of Central Florida, and one of the main architects of the New Horizons mission that reached Pluto for the first time, is one of the loudest critics of the IAU’s definition.
“It’s a sloppy definition,” said Metzger, who is the lead author of the new study. “They didn’t say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit.”
Metzger and colleagues reviewed a myriad of studies published over the past 200 years looking for any instance where the clearing of the orbit was used as a requirement for defining a planet. The authors found only one such mention — a study published in 1802 — which was based on flawed, now-disproven reasoning.
Instead, the researchers found over 100 recent examples where researchers had used the word planet in a way that would violate the IAU definition. “They are doing it because it’s functionally useful,” Metzger said.
“The IAU definition would say that the fundamental object of planetary science, the planet, is supposed to be a defined on the basis of a concept that nobody uses in their research,” Metzger says. “And it would leave out the second-most complex, interesting planet in our solar system.”
Moons such as Saturn’s Titan and Jupiter’s Europa have been called planets by scientists since the time of Galileo. It was in the early 1950s, when Gerard Kuiper published a study that made the distinction between planets and asteroids based on how they formed, that scientists started paying more attention to the division.
However, even this reason is no longer considered a factor that determines if a celestial body is a planet, Metzger says.
And since clearing orbit is obviously not a standard in the scientific literature, it shouldn’t have ever been used in the IAU’s controversial 2006 definition, the authors argue.
“We showed that this is a false historical claim,” said co-author Kirby Runyon, with Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “It is therefore fallacious to apply the same reasoning to Pluto.”
If that’s the case, when is an object worthy of being called a planet? The authors of the new study recommend classifying a planet based on its intrinsic properties rather than extrinsic ones that are subject to change, such as the dynamics of a planet’s orbit. Today, the debris and asteroids that fall into Pluto’s path are many, but they may disappear a billion years from now — so they shouldn’t be fundamental to describing a body.
Metzger says that a fundamental criterion to classifying a planet should be whether it’s large enough to allow gravity to mold the object into a sphere.
“And that’s not just an arbitrary definition,” Metzger says. “It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body.”
Modern observations, such as those performed by the New Horizons mission, revealed that Pluto has an active underground ocean, a multilayer atmosphere, organic compounds, and multiple moons.
“It’s more dynamic and alive than Mars,” Metzger says. “The only planet that has more complex geology is the Earth.”
Certainly, this isn’t the last word, but the lively debate is valuable and useful. At the end of the day, even if we might have hurt Pluto’s feelings, we’ll come out of this with a much clearer picture of what a planet looks like.
Among all the planets zipping around through space, the Earth is unique. It’s not the water. It’s not the pleasant climate. It’s not even the fact that Earth teeming with life.
According to one pseudoscientific current out there, what makes our planet unique is that it is flat.
Image credits NASA.
If you find that hard to swallow, fret not! The Earth is not actually flat, because that’s not how planets work. But since some people make a hobby, a killing on social media, or even a career out of championing the pseudoscientific cause of Flat Earth, we felt the need to push back — gently, with well-rounded facts.
Why are planets round?
The same thing that prevents you from floating out into space — gravity — is the same force that gives planets their curves.
Celestial bodies start life off as clouds of dust and gas. Then, something happens to compress all this matter, somewhere in the cloud, usually near its center. This can range from more extreme events — like a star going supernova somewhere nearby — to the mundane, such as a star or rogue planet disturbing the cloud with its gravitational wake.
The exact cause isn’t very relevant to this particular love story; some start with a bang, others with a slow and steady wooing. But, as long as that special someone comes and stirs the primordial cloud’s heart, planets will be born.
The firstborn are always stars. The increased pressure in the dust cloud brings hydrogen atoms closer and closer together. This starts a chain reaction as the center draws in more and more matter. Eventually, pressure increases enough that the hydrogen starts to fuse into helium and, tada! You have a star!
This process consumes much of the dust and gas in the cloud. For context, the Sun ate up some 99% of the matter in our system’s primordial cloud. From that remaining sliver of material, planets will accrete (form) through much the same mechanisms. Clumps of matter draw in material from the rings of dust around the star, fusing together into planets.
And here lies the crux of their roundness. Gravity draws matter in as the planet is forming. It pulls equally on all directions towards the core. It also gets more powerful the more mass a planet has. So, as the planet grows, every bit of matter gets pulled towards the center (down). In an effort to equalize strain (nature hates imbalances), these bits of matter will do everything in their power to be as close to the core as possible (a.k.a., they fall down). In three dimensions, the shape that best satisfies this requirement is a sphere.
Planets aren’t perfect spheres — they have features like mountains or valleys, and tend to form bulges around their equator — but they’re definitely, without a doubt, not flat.
Why aren’t planets flat?
Let’s assume for a second that you can make a flat planet. We’ll need a hypothetical, dense ‘core’ in the shape of a slab or disk to start with.
The problem is that this model is already unstable. Gravity as a force acts between the center of mass (COM) of two or more objects — and by mathematical definition, centers of mass are points, not volumes. Under the sway of gravity, particles will try to move as close as they possibly can to that center of mass. A slab or a disk simply has too many particles too far away from the center to be stable.
Let’s take a slab with uniformly-distributed mass as a case study. For a slab (or ‘cuboid’ for the geometry purists out there), the COM is the same as its geometric center — you can find this point at the intersection of its diagonals or its lines of symmetry. To keep it as simple as possible, I’ll leave you with this quote from Andy Ruina and Rudra Pratap’s book Introduction to Statics and Dynamics, from a chapter on centers of mass (page 81):
“The center of mass respects any symmetry in the mass distribution of a system. If the word ‘middle’ has unambiguous meaning in English then that is the location of the center of mass.”
Particles on the edges of the slab, or those around the lip of the disk, are subjected to different levels of gravitational strain — i.e. they are closer or farther away from this center of mass than their peers.
Image credits Alexandru Micu / ZME Science.
Image credits Alexandru Micu / ZME Science.
They’ll try to address this imbalance by ‘falling’ towards the center (of mass). So, in time, the edges of the slab will crumble and fall closer to the COM (so from point 1 towards point 3). In time they’ll pile around this point, further increasing its gravitational pull, drawing in more matter. Take this line of thought far enough and you’ll end up with a sphere because, in a sphere, all points are as close as possible to the center of mass.
Alternatively, if we consider the slab to be indestructible for debate’s sake, this mechanism still holds: any new material drawn by the slab’s gravitational pull will tend to pile as close to the COM as possible, in time forming a sphere.
Image credits Alexandru Micu / ZME Science.
Ok, but how do we know for sure that it’s not flat?
Well, we just talked about this, but sure.
The ancient Greeks are the first people we know of to consider a spherical Earth; the hypothesis popped up in the 5th century BC, in the works of Herodotus and later Pythagoras, to whom the spherical model is widely attributed. Since then, we humans have repeatedly shown that the Earth is, in fact, round.
A little over 2,000 years ago, a Greek mathematician named Eratosthenes (of Cyrene) — who was also the chief librarian at the Library of Alexandria — used shadows to do so. He lived in Alexandria but, the story goes, he learned that no vertical shadows were cast at noon on the summer solstice in the city of Syene, a little to the south of where he lived. Naturally, he wondered if the same would happen in Alexandria. Turned out, it didn’t. On June 21, he stuck a stick in the ground at noon and watched its shadow. It measured around 7 degrees.
Given the large distances involved, the sun’s rays are virtually parallel when they reach Earth; on a flat plane, they would hit the Earth at the same angle. But the fact that a stick in Alexandria cast a shadow while one in Syene didn’t demonstrates that these rays hit at differnt angles — that the planet is round. Eratosthenes, being the smooth Greek that he was, would go on to invent geography and calculate the Earth’s circumference. From the shadow of a stick.
A breakdown of Eratosthenes’ experiment. Image via Wikimedia.
The granddaddy-o of geography still doesn’t cut it? Ok, that’s fine. Let’s move on, then, to the first guy to almost-travel around (notice the subtle root-word ’round’ here) the Earth. Enter Magellan.
Loaded with money from the Spanish Crown, Ferdinand Magellan embarked on August 10, 1519, from Seville (Spain), at the lead of five ships. He sailed across the Atlantic, passed the Strait of Magellan, finally taking a little break in the province of Cebu in the Philippines. Where a bunch of natives murdered him in battle.
Sensing that things were Not Quite Right, second-in-command Juan Sebastián Elcano took charge and led the expedition back home. They arrived back in Seville on September 6, 1522, after fully circumnavigating the globe. Charles I of Spain rewarded Elcano with a coat of arms with the motto ‘Primus circumdedisti me’ (“You went around me first”).
The Transglobe Expedition (1979–1982) was the first expedition to make a circumpolar circumnavigation, traversing both poles of rotation (north and south) using only surface transport. Together with Magellan’s east-west circumnavigation, this proves that the Earth is a sphere.
Other evidence that the Earth is not flat come from multiple sources, ranging from geology to space flight.
Why write this?
While pseudoscientific schools of thought, flat-earthism among them, have always been around, they’re gaining a lot of ground in society today.
Part of that is owed to technology such as the Internet making it easier than ever before to share ideas and find like-minded individuals. But there’s another more worrying factor that drives this rise: an increased distrust of science and of ‘officially accepted’ narratives.
We here at ZME Science fully support discourse and the sharing of ideas, but we also feel like we have a responsibility to stand up for truth and scientific fact — for all the reasons we’ve detailed here.
The theory of flat Earth is by no means true, nor is it rooted in fact.
A team has now found evidence of iron and titanium vapors in the atmosphere of the hottest planet ever discovered.
Artistic depiction of KELT-9b orbiting its host star, KELT-9. Image credits: NASA/JPL-Caltech.
Planets don’t really get much hotter than KELT-9b. With a surface temperature well over 4,000 ℃, the planet was detected in 2017 using the Kilodegree Extremely Little Telescope, and the unusual finding raised quite a few eyebrows at the time.
KELT-9, the star around which the planet revolves, is located some 650 light years from Earth, in the constellation Cygnus (the Swan). It’s twice as hot as the Sun, but that’s not the reason why planet KELT-9b is so hot.
The reason is the orbiting distance: located 30 times closer than the Earth’s distance from the Sun, the planet revolves around its star in only 36 hours. As a result, temperatures reach 4,600° Kelvin (4,300 °C / 7,800 °F). That’s not quite as hot as the Sun, but it’s definitely hotter than many stars.
Artistic depiction of KELT-9b. Image credits: Denis Bajram.
Astronomers aren’t really sure what the planet’s atmosphere might look like. Initial observations revealed that the atmosphere mostly comprises of hydrogen, but now, a new study has revealed some of its less abundant elements. Theoretical models suggested that metallic elements might be present in its atmosphere.
“The results of these simulations show that most of the molecules found there should be in atomic form because the bonds that hold them together are broken by collisions between particles that occur at these extremely high temperatures,” explains Kevin Heng, professor at the University of Bern.
Now, using the HARPS-North spectrograph, astronomers discovered a strong signal corresponding to iron vapor in the planet’s spectrum. They also found evidence of titanium in vapor form.
“With the theoretical predictions in hand, it was like following a treasure map,” says Jens Hoeijmakers, a researcher at the Universities of Geneva and Bern and lead author of the study, “and when we dug deeper into the data, we found even more,” he adds with a smile. Indeed, the team also detected the signature of another metal in vapur form: titanium.
This newly discovered planet might force scientists to open up a new planetary category: so-called “ultra-hot Jupiters.” Hot Jupiters are a class of gas giant exoplanets that are generally similar to Jupiter, but orbit much closer to their star — and are therefore much hotter. Ultra-hot Jupiters are even closer to their star
KELT-9b might not be the only planet to boast such an atmospheric composition. However, astronomers believe that planets like it, orbiting so close to their star, may be obliterated by the hellish environment in the star’s proximity. KELT-9b seems massive enough to take the pummeling, but others may have not been so fortunate.
Journal Reference: Hoeijmakers et al. Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b. Nature, 2018; DOI: 10.1038/s41586-018-0401-y
Astronomers have snapped the first pictures of a planet forming.
This is the first clear image of a planet forming around the dwarf star PDS 70. Image credits ESO / Müller et al., 2018, A&A.
Researchers led by a group at the Max Plank Institute for Astronomy in Heidelberg, Germany, are spying on a baby planet. The object of their attention is a still-forming planet that orbits around PDS 70, a young dwarf star. This is the first time we’ve captured clear images of a forming planet and its travels through the dust cloud surrounding young stars.
The images were captured using the SPHERE instrument installed on Unit Telescope 3 of the European Southern Observatory (ESO’s) Very Large Telescope (VTL) array in Chile. SPHERE, the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument, is one of the most powerful planet-finding tools astronomers have at their disposal today. What makes SPHERE stand out in the field of exoplanet exploration is that, unlike the majority of its contenders, it relies on direct imaging — SPHERE takes actual photographs of planets millions or billions of kilometers away.
SPHERE relies on a technique known as high-contrast imaging to produce such amazing shots. The device uses complex observation techniques and powerful data processing algorithms to tease out the faint traces of light incoming from planets around bright stars. Astronomers draw on the Earth’s rotation to help them better observe such planets — SPHERE continuously takes images of the star over a period of several hours, while keeping the instrument as stable as possible. This creates images of a certain planet taken from slightly different angles and at different points in the stellar halo, giving the impression that it’s slowly rotating or moving about. The stellar halo, meanwhile, appears immobile. The last step is to combine all the images and filter out all the parts that do not appear to move — blocking out signals that don’t originate from the planet itself.
The new planet, christened PDS 70b, stands out very clearly in the images SPHERE recorded. It appears as a bright point to the right of that blackened blob in the middle of the image. That blob is a coronagraph — a mask that researchers apply directly onto the star, lest its light blocks out everything else in the image.
Some examples of how such images from different angles helps astronomers tease out the light incoming from exoplanets. Image credits Müller et al., 2018, A&A.
PDS 70b is a gas giant with a mass several times that of Jupiter. It’s about as far from its host star as Uranus is to the Sun. Currently, PDS 70d is busy carving a path through the planet-forming material surrounding the young star, the researchers note, making it instantly stand out.
“These discs around young stars are the birthplaces of planets, but so far only a handful of observations have detected hints of baby planets in them,” explains Miriam Keppler, who lead the team behind the discovery of PDS 70’s still-forming planet. “The problem is that until now, most of these planet candidates could just have been features in the disc.”
PDS 70d is already drawing a lot of attention from astronomers. A second paper, which Keppler also co-authored, has followed-up on the initial observations with a few months of study. The data from SPHERE also allowed the team to measure the planet’s brightness over different wavelengths — based on which they estimated the properties of its atmosphere. The planet is blanketed in thick clouds, the team explained, and its surface is currently revolving around a crisp 1000°C (1832°F), which is much hotter than any planet in the Solar System.
The findings also helped researchers make heads and tails of a structure known as a transition disc. This is a ring-like protoplanetary (meaning it is involved in early planetary formation) structure. Transitional disks roughly resemble a stadium, with a clean area in the middle (from which planets drew their matter), surrounded by a ring of dust and gas. While these gaps have been known for several decades now and speculated to be produced by the interaction between forming planets and its host star’s disk, this is the first time we’ve actually seen them.
“These objects represent […] disks whose inner regions are relatively devoid of distributed matter, although the outer regions still contain substantial amounts of dust,” explains a paper published by Strom et al. in 1989.
All this data helps flesh out our understanding of the early stages of planetary evolution — which are quite complex and, up to now, “poorly-understood”, according to André Müller, leader of the second team to investigate the young planet.
“We needed to observe a planet in a young star’s disc to really understand the processes behind planet formation,” he explains.
The findings further help improve our overall knowledge of how planets form. By determining PDS 70d’s atmospheric and physical properties, astronomers now have a reliable data point from which to extrapolate — which will help improve the accuracy of our planetary formation models.
Not bad for a bunch of photographs.
The first paper, “Discovery of a planetary-mass companion within the gap of the transition disk around PDS 70” has been published in the journal Astronomy & Astrophysics.
The second paper, “Orbital and atmospheric characterization of the planet within the gap of the PDS 70 transition disk,” has also been published in the journal Astronomy & Astrophysics
One team of NASA scientists wants to set an old wrong right — by making Pluto, among other cosmic bodies, a ‘planet’ again.
Haze on Pluto at far higher altitudes than expected, sighted by the New Horizons mission. Image credits NASA / JPL.
Back in 2006, the International Astronomical Union (IAU) announced that the word “planet” is getting a new definition. The new interpretation excluded many celestial bodies, including Pluto. Something which many people, including yours truly, considered to be a great injustice and plain Not Cool. Luckily, other people agree with me — more to the point, a group of NASA planetary scientists agrees with me.
And what they’re planning might turn Pluto back into the planet it never ceased to be.
A geophysical definition of planets
“It’s bullshit,” is how Alan Stern, principal investigator of NASA’s New Horizons mission to Pluto, sumarrises its exclusion from the rank of ‘official’ planet.
Stern is leading a team of NASA researchers who are proposing a new definition of planets — one that goes further than simply re-instating icy Pluto. The proposal’s goal is to redefine what we consider ‘a planet’, and tie that definition to very simple, easily observable factors.
In NASA fancy-speak, they want any “sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters” to be considered a planet. In common English, they basically want to define planets as the bodies that are big enough to become spherical-ish under their own gravitation, aren’t so big they’ll ignite into a star, and orbit around something — anything, really.
“Why do we say this? We are planetary scientists, meaning we’ve spent our careers exploring and studying objects that orbit stars. We use “planet” to describe worlds with certain qualities,” Stern wrote for the Washington Post.
“When we see one like Pluto, with its many familiar features – mountains of ice, glaciers of nitrogen, a blue sky with layers of smog – we and our colleagues quite naturally find ourselves using the word “planet” to describe it and compare it to other planets that we know and love.”
Some of you may already suspect that the definition this group is proposing also covers a lot of moons — even Earth’s own. The team says this isn’t an oversight, rather, it’s an intended extension of the definition, one that acknowledges the practical realities of day-to-day planetary science.
“Moon refers to the fact that they orbit around other worlds which themselves orbit our star,” Stern continues “but when we discuss a world such as Saturn’s Titan, which is larger than the planet Mercury, and has mountains, dunes and canyons, rivers, lakes and clouds, you will find us – in the literature and at our conferences – calling it a planet. This usage is not a mistake or a throwback. It is increasingly common in our profession and it is accurate.”
The proposed definition also patches some of the gaps in the current IAU planetary classification system:
Under the current system, only planets orbiting our Sun are ‘planets’. Those orbiting other stars, those orbiting freely in the galaxy (rogue planets) aren’t considered to be real ‘planets’.
Secondly, the IAU system requires that planets “clear their neighborhood” (also known as zone-clearing) — that during formation they become large enough for their gravitational pull to bring in and ‘clear’ all matter in their proximity. The problem with this criterion is that “no planet in our Solar System” can satisfy it, the team notes, since there is a number of small cosmic bodies constantly flying through planetary orbits; Earth’s included.
Finally, what the team considers “most severe”, is that zone-clearing is size-dependent: in other words, the criterion becomes completely arbitrary because you can define its “zone” any way you want.
The team agrees that given the breakneck rate at which new planets and new planetary types have been discovered in recent decades, it made sense to ask which kind of objects should be classed as planets. But they also contend that the “process […] was deeply flawed and widely criticized even by those who accepted the outcome.” During the 2006 conference, where the standards were adopted, “the few scientists remaining at the very end of the week-long meeting (less than 4 percent of the world’s astronomers and even a smaller percentage of the world’s planetary scientists) ratified a hastily drawn definition that contains obvious flaws,” Stern adds.
The team is confident that the IAU will reconsider the flaws in its definition sooner or later. And even if that doesn’t happen, Stern says that eventually, this officially-sanctioned definition will have to align itself to “both common sense and scientific usage.”
“The word “planet” predates and transcends science. Language is malleable and responsive to culture,” he concludes.
“Words are not defined by voting. Neither is scientific paradigm.”
The proposal “A geophysical planet definition” has first been presented last March at the annual Lunar and Planetary Science Conference in Houston, Texas.
Artist impression of an early solar system. Credit: NASA.
About a decade ago, a violent explosion roughly 23 miles above the surface sent incendiary fragments hurling towards the dunes of the Nubian desert in Sudan. In and of itself, the event was not necessarily impressive, apart from the fancy light show — after all, our planet is constantly bombarded by relatively small objects. But, according to a new study, these meteorites have a much more dramatic origin and history than meets the eye. Scientists say that under the meteorites’ thick carbonized exterior hid diamonds which enclosed remnants of a long-lost planet or planetary embryo during the crazy days of the early solar system.
It was mighty crowded back then
A jeweler wants diamonds to be perfect, meaning impurities should be kept to a minimum, ideally none at all. However, a diamond with inclusions is far more valuable from a scientific standpoint than a so-called flawless jewel. Because diamonds are forged at immense pressures and temperatures, typically deep inside the planet, the various materials that get trapped inside are quite hard to get a hold of at the surface — and diamonds can preserve them for billions of years.
The team led by Farhang Nabiei of the Ecole Polytechnique Federale de Lausanne in Switzerland was initially investigating the relationship between the diamonds and the layers of graphite surrounding them, when they realized the small pockets of material trapped inside looked far more interesting. With the help of a high-power electron microscope, the researchers studied the tiny diamonds inside a thin section of the meteorite and were astonished to learn they were formed at incredibly high pressures — much higher than any kind of pressure the meteorites might have been subjected to when they crashed into Earth.
A chemical map shows sulfur (red) and iron (yellow) inside the inclusions in the diamond matrix. Credit: Dr. F. Nabiei/Dr. E. Oveisi, EPFL, Switzerland.
Specifically, the diamonds must have formed at 20 gigapascals, which is the kind of pressure found deep within a planet the size of Mars or Mercury — but the meteorites come from neither of these planets or any other planet that we know of for that matter. The meteorites have, in fact, been classed as ureilites — a rare type of stony meteorite that has a unique mineralogical composition, very different from that of other stony meteorites. Transmission electron microscopy also revealed traces of chromite, phosphate, and iron-nickel sulfides inside the larger diamonds, which are inclusions that can be found in Earth’s diamonds, too. It’s the first time such inclusions have been identified inside extraterrestrial diamonds.
A colorized image shows the diamond phase (blue), inclusions (yellow) and the graphite region. Credit: Dr. F. Nabiei/Dr. E. Oveisi/Prof. C. Hébert, EPFL, Switzerland.
The size of the diamonds is another clue that we’re dealing with some very peculiar objects. Their average size is about 100 microns, which is about the size of a human hair. That may not sound like much, but that’s still larger than any diamond that could possibly form by shock transformation of graphite (i.e. when a meteorite crashes on Earth). This suggests that the diamonds formed deep in a body’s interior and not on impact. Such a planetary-sized body is now long gone, having been destroyed in a cataclysmic game of billiard early on in the solar system’s history. These early proto-planets would have been hurled towards each other by a tug of war between the gravities of a young Jupiter and the sun. The environment likely looked very crowded too, with multiple Mars-sized protoplanets destined to collide into each other.
“This study provides convincing evidence that the ureilite parent body was one such large ‘lost’ planet before it was destroyed by collisions [some 4.5 billion years ago],” researchers wrote in the new paper on the subject, published this week in the journal Nature Communications.
The discovery offers new insight into our solar system’s tumultuous past, helping piece together how it all came to be. This is merely the beginning, as hundreds of other ureilites could offer new clues to the nature of the early solar system and the evolution of its planets.