Tag Archives: gas giant

Saturn rings.

Saturn’s rings are raining down — in about 100 million years, they’ll be gone

New research from NASA found that Saturn, the ring planet, is losing its rings.

Saturn and rings.

Image NASA / Cassini Imaging Team via Wikimedia.

Observations made decades ago by Voyager 1 and Voyager 2 show that Saturn is devouring its own rings, NASA reports. The particles making up these striking structures are falling onto the planet as a rain of dust and ice, propelled by Saturn’s gravity and magnetic field.

One ring to bind them

“We estimate that this ‘ring rain’ drains an amount of water products that could fill an Olympic-sized swimming pool from Saturn’s rings in half an hour,” said James O’Donoghue of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, the study’s lead author.

“[…] The rings have less than 100 million years to live. This is relatively short, compared to Saturn’s age of over 4 billion years.”

The research actually began with scientists trying to figure out if Saturn formed with its rings or acquired them later. The second scenario seems to be the more likely, the team reports. In fact, they estimate that the rings are no older than 100 million years. The team based this age on how much it would take for the C-ring to form from a (hypothetical) original B-ring-like structure. Here’s a chart for your convenience:

Saturn rings.

Saturn rings and with their major subdivisions.
Image credits NASA / JPL / Space Science Institute via Wikimedia.

There are quite a number of theories in regards to how Saturn got its rings (the most prevalent of which we’ve talked about here). If they’re younger than the planet itself, the rings could be the product of collisions between Saturn and small, icy moons. Such a mechanism would be supported by the rings’ present makeup — chunks of water ice ranging from several yards across to microscopic sizes.

Still, the finding that Saturn acquired its rings later in life is, perhaps, overshadowed by the realization that it’s eventually going to lose them. O’Donoghue says, we’re “lucky to be around” while Saturn still has rings. They’re probably around the middle of their lifetime, he adds. The other side of the coin is that we’ve perhaps missed out on seeing similarly lush ring systems around Jupiter, Uranus, and Neptune. While these gas giants do have ring systems today, they’re thin, wispy things.

Black belt giant

The first hints that Saturn’s rings were raining down on the planet came from Voyager readings on (seemingly) unrelated phenomena: variations in Saturn’s ionosphere (electrically-charged upper atmosphere), density variations in its rings, and the planet’s three dark bands These bands encircle the planet at high altitudes (stratosphere) at northern mid-latitudes, and were first spotted by the Voyager 2 mission in 1981.

Later, a NASA Goddard researcher named Jack Connerney linked (paper here) these bands to the planet’s massive magnetic field. Connerney’s hypothesis was that the bands form as electrically-charged ice particles from Saturn’s rings flowed down magnetic field lines. Tiny particles can get electrically charged by ultraviolet light from the Sun or by plasma clouds emanating from micrometeoroids impacting the rings.

Essentially, water pouring into the planet’s upper atmosphere was what formed these bands. The water would literally wash away haze in Saturn’s stratosphere, making them less reflective of light — so the bands appear darker.

So what actually causes the rings to rain down? Well, they’re generally kept in orbit by an interplay between the planet’s gravitational field (which pulls them down) and the centrifugal force generated by the rings’ rotation (which pushes them outwards, or ‘up’).

Things become more complicated when Saturn’s magnetic field gets involved, however. Those electrically-charged particles we talked about earlier also start feeling the pull of the planet’s magnetic field, which curves towards Saturn at its rings. In some parts of the rings, this magnetic pull is enough to dramatically shift the balance of forces on particles — it neutralizes, to an extent, the centrifugal force. Gravity takes hold, pulling the particles down on the planet.

These infalling bits of water chemically react in Saturn’s ionosphere, generating H3+ ions. O’Donoghue picked up on these ions using the Keck telescope in Mauna Kea, Hawaii, as H3+ ions glow in infrared light. The team saw glowing infrared bands in Saturn’s northern and southern hemispheres where magnetic field lines enter the planet. By analyzing the infrared light output, the team calculated the quantity of infalling ring matter (i.e. of how fast they are degrading).

The highest influx of infalling ice, the paper adds, is found in an area in southern Saturn. Some of the matter spewed by Enceladus’ ice geysers also finds its way down to the gas giant, which Connerney says isn’t “a complete surprise.”

So far, the results are pretty solid. However, the team says observing Saturn as it goes around the sun (on a 29.4-year orbit) would conclusively prove or disprove the findings. On its trek, Saturn’s rings will be exposed to various degrees of ultraviolet light — which charges ice particles in the rings. If researchers find that different levels of exposure to sunlight change the quantity of ‘rain’ on Saturn, the study’s conclusions would be confirmed.

The paper “Observations of the chemical and thermal response of ‘ring rain’ on Saturn’s ionosphere” has been published in the journal Icarus.

It Is Possible Jupiter Could Support Life, Scientists Say

Jupiter and its shrunken Great Red Spot. Credit: Wikimedia Commons.

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.

NASA cancels maneuver to get Juno closer to Jupiter due to faulty fuel valves — but that’s not bad news

NASA’s Science Mission Directorate has canceled a planned tightening of Juno’s orbit around Jupiter after system checks revealed faulty fuel valves on board the probe.

Image credits NASA / JPL.

Last year on July 4, the Juno probe reached its destination and settled in a comfortable 53-day orbit around Jupiter. On the closest point to the giant during every pass, it would deploy its sensor array and take as many measurements as possible, beaming the data back to Earth for study.

Researchers hoped to reduce Juno’s orbit around the gas giant down to just 14 days to speed up data acquisition from the craft. To do this, they planned on firing the craft’s main engine to reduce its speed and get it closer to Jupiter. Operational tests performed before the braking however showed the two helium check valves which supply the engine did not operate as expected when the system was fully pressurized.

“Telemetry from the spacecraft indicated that it took several minutes for the valves to open, while it took only a few seconds during past main engine firings,” a NASA status report on Friday read.

Rather than risk to lose control on Juno’s current orbit, NASA postponed the maneuver. Since then, researchers have been hard at work looking into how the burn can safely be performed in light of the new technical difficulties.

But it seems they weren’t very confident in their chances. Last week, NASA announced it will abort the maneuver rather than risk to irrevocably alter Juno’s flight path. The probe will maintain its current orbit around Jupiter.

“We looked at multiple scenarios that would place Juno in a shorter-period orbit, but there was concern that another main engine burn could result in a less-than-desirable orbit,” said project manager Rick Nybakken with NASA’s Jet Propulsion Laboratory in Pasadena, California. “The bottom line is a burn represented a risk to completion of Juno’s science objectives.”

The good news is that the probe can still perform its task, it will just take a little longer to do so. Both orbits would yield the same quality of data, as they would both take Juno just as close to Jupiter — some 2,600 miles (4,200 km) above the gas giant’s clouds.

Which is not a bad place to be at all, judging from the view.
Image credits Credits: NASA/JPL-Caltech/SwRI/MSSS/Roman Tkachenko.

“The worst-case scenario is I have to be patient and get the science slowly,” lead researcher Scott Bolton, with the Southwest Research Institute in San Antonio, Texas, said after the engine problem surfaced in October.

“The science will be just as spectacular as with our original plan,” he added on Friday’s release.

“In fact, the longer orbit provides new opportunities that allow further exploration of the far reaches of space dominated by Jupiter’s magnetic field, increasing the value of Juno’s research,” the statement added.

Another upside of canceling the burn is that a more distant orbit will extend the craft’s operational life. Jupiter’s massive radiation belts were the main killer for Juno, and staying well away from them should better protect its systems.

In light of its extended operational life, Nybakken will probably request additional funding for the US$1.13 billion mission, currently scheduled to end on July 31, 2018 — when Juno would have completed its observations and become inoperable under the effects of radiation. The extended mission now aims at completing 12 close approaches.

Juno has proven instrumental in our understanding of how gas giants form and behave. If you want to take a more active part in its research, you can vote on which features of the planet will be imaged during each flyby in the JunoCam project set up by NASA. It’s the closest you’ll ever get to be an astronaut without even leaving your chair.

Jupiter May Have Ejected Solar System's Fifth Giant Planet. Image: U Toronto

Jupiter may have ousted a fifth gas giant out of the solar system 4 billion year ago

Jupiter May Have Ejected Solar System's Fifth Giant Planet. Image: U Toronto

Jupiter May Have Ejected Solar System’s Fifth Giant Planet. Image: U Toronto

Four billion years ago, our planet was nothing like today. With a thin atmosphere and a crust barely formed, Earth was subjected to constant bombardments from meteors and asteroids and any water was boiled immediately. It was chaos, but Earth wasn’t alone. These were the early days of the solar system and elsewhere other planets were having a tough time. For instance, there’s this hypothesis that there was in fact an additional planet in the early solar system (at least one). This tentative “fifth gas giant” was supposedly ejected out of the solar system due to a gravitational tug of war between other planets. Now, a new study by researchers at the University of Toronto seems to suggest that Jupiter exerted the most influence over this planetary ejection.

The idea was first suggested in 2011 by David Nesvorný of the Southwest Research Institute. By simulating the formation of the solar system,  Nesvorný found that for the solar system to reach its current configuration,  an additional Neptune-mass planet between Saturn and Uranus must have existed. Since this planet doesn’t exist anymore, the only feasible possibility is that it was ejected, and this isn’t as crazy at it sounds. If a planet encounters another much more massive planet, it could become accelerated to such a degree that it breaks free from the the massive gravitational pull of the Sun.

“The possibility that the solar system had more than four giant planets initially, and ejected some, appears to be conceivable in view of the recent discovery of a large number of free-floating planets in interstellar space, indicating the planet ejection process could be a common occurrence,”  Nesvorny said at the time.

University of Toronto investigated this possibility by employing a forensic technique of sort. Namely, they studied the orbits of the gas giant satellites since such a violent encounter must have left a mark on these moons.

They made computer simulations based on modern-day trajectories of Callisto and lapetus, the regular moons orbiting around Jupiter and Saturn respectively. They then measured the likelihood of each one producing its current orbit in the event that its host planet was responsible for ejecting the hypothetical planet, an incident which would have caused significant disturbance to each moon’s original orbit. Results show the event is 42% probable for Jupiter, while there is only 1% chance for Saturn.

“Ultimately, we found that Jupiter is capable of ejecting the fifth giant planet while retaining a moon with the orbit of Callisto,” said Ryan Cloutier, a PhD candidate in U of T’s Department of Astronomy & Astrophysics and lead author of a new study published in The Astrophysical Journal. “On the other hand, it would have been very difficult for Saturn to do so because Iapetus would have been excessively unsettled, resulting in an orbit that is difficult to reconcile with its current trajectory.”

Biggest Planets Started out as Tiny Pebbles

Gas giants like Saturn or Jupiter may have formed not from a planetary core, but rather from tiny pebbles that stuck together. This theory would solve one of the biggest problems about our understanding of planetary formation: the timeline.

Artistic depiction of planetary accretion. Image via Planetary Hunters.

The previous model was called core accretion: you have a planetary core of rock and ice that starts to attract and keep other rocky objects, forming a larger and larger object, until it has enough gravitational attraction to start pulling gas and dust, creating a gas giant. But Jupiter’s and Saturn’s core is huge, much larger than the entire Earth, and that’s a problem.

The two gas giants must have formed very early in our solar system, because the formation of gas giants typically only lasts for 10 million years – compared to the Earth, whose formation lasted some 30 million years. But how could the same process create a much larger core in 10 million years than it did in 30 million years?

“The timescale problem has been sticking in our throats for some time,” Hal Levison, scientist in the SwRI Planetary Science Directorate and lead author of the paper, said in a statement. “It wasn’t clear how objects like Jupiter and Saturn could exist at all.”

He, alongside SwRI research scientist Katherine Kretke and Martin Duncan, a professor at Queen’s University in Kingston, Ontario came up with a solution for that problem; they call it the pebble accretion model.

The interior of the gas giants. Credit: RHorning/wikimedia

Pebble accretion involves much smaller pieces of rock, ranging from between one centimetre and one metre in size (0.4in to 3.3ft) – yes, they’re actual pebbles. These pebbles accumulate together and ultimately collapse under the growing gravity, attracting more pebbles. At a first glance, this seems counter-intuitive. I mean, the process is pretty similar to core accretion, except you start out with smaller rocks, so it should be slower, but this continuous movement creates winds, which can blow pebbles towards the accumulating core.

“If the pebbles form too quickly, pebble accretion would lead to the formation of hundreds of icy Earths. The growing cores need some time to fling their competitors away from the pebbles, effectively starving them. This is why only a couple of gas giants formed,” Kretke explained.

This model hasn’t been confirmed and it will be very difficult to confirm it directly, but it seems to fit with the existing objects in our solar system.

“As far as I know, this is the first model to reproduce the structure of the outer solar system, with two gas giants, two ice giants (Uranus and Neptune), and a pristine Kuiper belt,” Levison said.

 

Artist's impression of the "rogue planet" CFBDSIR2149 discovered in the AB Doradus group of moving stars. (European Southern Observatory/AFP)

Closest rogue planet discovered is just 100 light-years away

Like in a scene from a Sci-fi novel, about 100 light years away, somewhere in the constellation Doradus, a planet is travelling around the galaxy by itself, without orbiting a parent star. This “rogue planet“, has a temperature of about 400C and a mass between 4 to 7 times that of Jupiter – close to the mass limit beyond which it would have become a brown dwarf.

The object, that so far has the captivating name of CFBDSIR2149, has been discovered while observing a region of space occupied by a group of about 30 stars called the AB Doradus Moving Group – a group of stars that have formed at the same time – most likely from the same initial gaseous nebulae. This fact was derived from the similarities in the composition, age and the similar direction of movement through space of the stars – which place the age of this group somewhere between 50 and 120 million years old – a reasonably young star group.

Artist's impression of the "rogue planet" CFBDSIR2149 discovered in the AB Doradus group of moving stars. (European Southern Observatory/AFP)

Artist’s impression of the “rogue planet” CFBDSIR2149 discovered in the AB Doradus group of moving stars. (European Southern Observatory/AFP)

The initial observations placed the object in the category of brown dwarfs – a class of sub-stellar objects – that are more massive then the biggest planets – the gas giants, yet they don’t have enough mass to start nuclear fusion. However, further analyses revealed that our object was in fact smaller than this – making it a planet – a gas giant. The whole detection was possible due to the fact that our “rogue” emits light in the infrared wavelengths.

Astronomers said that based on its estimated age, through computer models of planetary evolution, they were able to make further deductions regarding the planet’s mass – 4 to 7 times the mass of Jupiter, and surface temperature of 400 degrees Celsius (750 degrees Fahrenheit).

The planet was discovered during a survey using the infrared cameras of the Canada-France-Hawaii Telescope on Hawaii’s Mauna Kea and the Very Large Telescope (VLT) in Chile, as study co-author Etienne Artigau of the University of Montreal said: “This object was discovered during a scan that covered the equivalent of 1,000 times the [area] of the full moon.

Of course, this is not the first time such a “nomad planet” has been spotted, but this observation is special because it found the closest such object discovered so far – only 100 light years away, the first such planet that is relatively close to our solar system, as study co-author Etienne Artigau put it: “We observed hundreds of millions of stars and planets, but we only found one homeless planet in our neighbourhood“.

A big question in the case of all such rogue planets is how this planet came to be? Maybe it formed inside a solar system, just as any other planet, and got ejected afterwards – through gravitational interaction perhaps with a more massive object entering that system. Or it formed separate from any solar system from the beginning, similar to the formation of a star – through progressive accretion of the gas of a dense nebulae. This question remains open – and perhaps will remain for some time to come.

Philippe Delorme of France’s Institute of Planetology and Astrophysics said: “these objects are important, as they can either help us understand more about how planets may be ejected from planetary systems, or how very light objects can arise from the star formation process.”

The findings were reported in the journal Solar and Stellar Astrophysics.

source: BBC

Stars create gaps devoid of gas giants, supercomputer simulation shows – contradicted by our own solar system

Gas giants might just be the most whimsical planets of all: they don’t just settle at any old point on the orbit – instead, they only choose certain regions and stay clear of others – at least according to a new supercomputer simulation.

A new study recently revealed that the orbital deserts and pile-ups caused by these preferences might actually be caused by starlight itself. Using supercomputer simulations of young solar systems, astronomers Richard Alexander of the University of Leicester in the United Kingdom and Ilaria Pascucci of the University of Arizona’s Lunar and Planetary Laboratory have found that powerful ultraviolet and X-ray emissions from the star tend to carve out empty spaces.

When planetary systems are formed, planets initially start out as spinning disks of dust and gas particles, and some clump in to form planets or satellites, while some only live to be comets, asteroids, or other such bodies.

“The disk material that is very close to the star is very hot, but it is held in place by the star’s strong gravity,” said Alexander in a press release from the University of Arizona. “Further out in the disk where gravity is much weaker, the heated gas evaporates into space.”

Around a star like our Sun, these gasless gaps seem to form 100 million to 200 million miles from the star.

“The planets either stop right before or behind the gap, creating a pile-up,” said Pascucci in the press release. “The local concentration of planets leaves behind regions elsewhere in the disk that are devoid of any planets. This uneven distribution is exactly what we see in many newly discovered solar systems.”

However, while this model seems correct enough, and was validated by other solar systems, our own solar system seems to stand in contradiction. Earth orbits the sun at a distance of about 93 million miles, where the void should begin, while Jupiter, the closes gas giant to the Sun, orbits at about 500 million miles. Time, however, will tell if Alexander and Pascucci’s model is correct, as telescopes discover more and more different solar systems.

Astronomers unveil densest rocky planet: ‘super rocky exotic Earth’

The planet in case is 55 Cancri e, and it’s 60 per cent larger in diameter than Earth but eight times as massive, which makes it twice as dense as Earth, and almost as dense as lead.

Earth like rocky planets

Credit: Jason Rowe, NASA Ames and SETI Institute and Prof. Jaymie Matthews, UBC

 

Generally speaking, planets come in two flavours: rocky earth-like planets, or gas giants (take Jupiter as an example). Our planet is also denser than you’d think at a first glance (5.51 grams per cubic centimeter), due to the immense pressure in the mantle and in the corse.

Rocky planets are made mostly out of silicate rocks and/or metals, and their density can vary greatly. If we take the rocky planets in our solar system for example, Mercury has a density of 5.4, Venus 5.2, and Mars only 3.9 (again, grams per cubic centimeter). If we are to talk in masses, the Earth weighs about as much as all the other rocky planets put together.

The super rocky exotic Earth

55 Cancri e is located about 40 light years from Earth, and it orbits a star extremely closely; so close that in fact its whole year is only 18 hours long.

“You could set dates on this world by your wrist watch, not a calendar,” says UBC astronomer Jaymie Matthews.

Due to its proximity to the star, temperatures on the planet rise to about 2700 degrees Celsius.

“Because of the infernal heat, it’s unlikely that 55 Cancri e has an atmosphere,” says lead author Josh Winn of MIT. “So this is not the type of place where exobiologists would look for life.”

However, even though 55 Cancri e isn’t of interest for exobiologists, it is of interest to astronomers and astrohysicists, who will definitely be “visiting” it in the nearby future.

“The brightness of the host star makes many types of sensitive measurements possible, so 55 Cancri e is the perfect laboratory to test theories of planet formation, evolution and survival.”

Even though the planet isn’t visible, even with a telescope, the star will be visible with the naked eye for the next two months, if the nightsky is clear.

“It’s wonderful to be able to point to a naked-eye star and know the mass and radius of one of its planets, especially a distinctive one like this”.