Tag Archives: goldilocks area

TRAPPIST-1, the dwarf star with seven Earth-sized planets, is older than our solar system

The solar system with seven potentially habitable planets is much older than our own.

This illustration shows what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right).
Credits: NASA/JPL-Caltech

TRAPPIST-1, with the much less attractive technical name 2MASS J23062928-0502285, is an ultra-cool brown dwarf just slightly larger than Jupiter. Despite its small size and low temperature, it’s one of the most interesting stars we’ve discovered out there. In February this year, NASA announced the discovery of seven Earth-sized planets around the star, all in the habitable zone — the so-called Goldilocks area where it’s just the right temperature for liquid water to exist. To make things even more exciting, this solar system is a ‘mere’ 40 light years away. It’s far enough to be inaccessible for the foreseeable future, but given the sheer immensity of our galaxy, 40 light years is just peanuts.

But having an Earth-like figure and being located in the habitable zone isn’t nearly enough to support life. That’s why astronomers at NASA have been studying the system assiduously, trying to learn more about it and establish its conditions. Now, for the first time, they’ve put an age on it — or rather, an age range. TRAPPIST-1 is between 5.4 and 9.8 billion years old. This makes it a very old system compared to our own, which is ‘just’ 4.5 billion years old.

It’s indeed a very broad range, but at least it enables us to say that the system is old, though we’re not yet sure how old. Also, while it’s a broad constraint, it’s still a constraint. When it was first discovered, we only knew that the star had to be older than 0.5 billion years, since that’s how long it takes for these stars to contract. It could have been almost as old as the universe itself.

“Our results really help constrain the evolution of the TRAPPIST-1 system, because the system has to have persisted for billions of years. This means the planets had to evolve together, otherwise the system would have fallen apart long ago,” said Adam Burgasser, an astronomer at the University of California, San Diego, and the paper’s first author.

The system overlaid over the habitable zone.
Image credits: NASA/JPL.

It’s not clear exactly what this means for the habitability of the planet. It’s known that older stars tend to flare less than younger stars, thus having less of a chance of wiping out potential life. But this also means that the planets have absorbed billions of years of high-energy radiation, which might imply that their atmospheres have boiled off. A decent analogy here is Mars, which once hosted an atmosphere which has since been wiped off by radiation.

But there are more aspects to consider. TRAPPIST-1 planets have lower densities than Earth, which makes it more likely for them to hold vast reservoirs of volatile molecules, which could generate thick atmospheres, strong enough to protect the planets from radiation. Especially the two outer planets, planet and planet h might have been lucky enough to escape with an atmosphere.

But if any life exists on these planets, it’s almost certainly way more hardy than that on Earth.

“If there is life on these planets, I would speculate that it has to be hardy life, because it has to be able to survive some potentially dire scenarios for billions of years,” Burgasser said.

TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its seven planets orbit very close to it, which puts them in the Goldilocks area.
Credits: NASA/JPL-Caltech

Future observations will focus on identifying potential atmospheres around these planets. If such an atmosphere exists, then it likely existed for billions of years, which makes the possibility of extraterrestrial life significantly more likely. The observations will also help astronomers better understand other similar systems form and develop.

“These new results provide useful context for future observations of the TRAPPIST-1 planets, which could give us great insight into how planetary atmospheres form and evolve, and persist or not,” said Tiffany Kataria, exoplanet scientist at JPL, who was not involved in the study.


‘Goldilocks area’ not nearly enough for habitable planets – internal temperature is also important

A Yale University researcher claims that the so-called Goldilocks planetary area only tells half of the story – in order for a planet to have the necessary temperature to support life, the starting internal temperature also needs to be right.

A new study suggests a planet must start with an internal temperature that is “just right” in order to support life. Credit: Michael S. Helfenbein/Yale University

In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star in which a planet can support liquid water, the fundamental condition for life as we know it. This habitable zone is colloquially called the ‘Goldilocks area’ as a metaphor from the beloved children’s fairy tale.

Since the concept was first presented in 1953, many planets have been shown to have a Goldilocks area, and some of them have one or several planets in this area. Naturally, distance from the star is the main factor. In our solar system, Venus is too close to the Sun, Mars is too far away, but Earth is at just the right distance.

Astronomers generally thought that a planet’s mantle might self-regulate the general temperature through convection (hot plumes are lighter, they rise towards the surface, they cool down, become heavier and sink again, creating a regulating mechanism). However, this might not be the case, and if this is not the case then the distance to the star isn’t the be-all end-all for temperature.

“If you assemble all kinds of scientific data on how Earth has evolved in the past few billion years and try to make sense out of them, you eventually realize that mantle convection is rather indifferent to the internal temperature,” said Jun Korenaga, author of the study and professor of geology and geophysics at Yale. Korenaga presents a general theoretical framework that explains the degree of self-regulation expected for mantle convection and suggests that self-regulation is unlikely for Earth-like planets.

The implications of this are huge, and might force us to tighten the leash on what we thought to be Earth-like planets.

“The lack of the self-regulating mechanism has enormous implications for planetary habitability,” Korenaga said. “Studies on planetary formation suggest that planets like Earth form by multiple giant impacts, and the outcome of this highly random process is known to be very diverse.”

The curious thing is that mantle convection does exist, at least on Earth. But Korenaga says that if our planet’s starting temperature wasn’t in the right range, this would have never happened.

“What we take for granted on this planet, such as oceans and continents, would not exist if the internal temperature of Earth had not been in a certain range, and this means that the beginning of Earth’s history cannot be too hot or too cold.”

The research was published in the journal Science Advances.

Potentially habitable planet found close to our solar system

It’s the closest Earth-like planet we’ve ever discovered: Wolf 1061c lies in the habitable zone, joining a very elite list of rocky planets that could host life.

The planet, reported in the Astrophysical Journal Letters, is one of the three planets found by astronomers around a small red dwarf star called Wolf 1061 in the constellation Ophiuchus.

“The middle planet Wolf 1061c, is orbiting within the so-called ‘Goldilocks zone‘ — the habitable zone where it might be possible for liquid water and maybe even life to exist,” said the study’s lead author Dr Duncan Wright of the University of New South Wales.

The planet, which has a mass four times higher than that of Earth, is located at only 14 light years away from us. As a reference, Alpha Centauri, the closest solar system to ours lies 4.24 light years from the Sun, and Pluto is about 6 light hours away. This makes Wolf 1061c our solar neighbor, but it still makes it too far to explore with today’s technology.

“This discovery is especially exciting because the star is extremely calm. Most red dwarfs are very active, giving out X-ray bursts and super flares which spells doom for any life, given the habitable zone is so close into these stars.”

While a few other planets have been found closer, they’re not even close to being considered habitable. Its star has a quarter of the mass of the Sun and about half its temperature, but Wolf 1061c lies closer to its star than the Earth does to the Sun. The system itself could be very old, astronomers suggest.

“After looking at several thousand planetary candidates we found that our Sun is a particularly quiet star, even quieter than your average Sun-like star,” said Dr Wright. “And the same is true for Wolf 1061, which is a particularly quiet star and is probably indicative that it’s a very old system.”

The planets were discovered through the so-called wobble method. Basically, just like star keeps the planets in place through its gravitational force, so too do the planets exert a (much smaller) gravitational attraction to their star, which makes it wobble ever so slightly. By studying these wobbles, astronomers can indirectly identify the planets around the star and infer its properties.

“We actually see the entire star wobbling back and forth due to the gravitational tug of the planets as they orbit around the star,” said Dr Wright.

It seems like red dwarfs, stars that are smaller and a cooler than the Sun are most likely candidates to host habitable planets, and red dwarfs are also by far the most common type of star in the Milky Way, at least in the neighborhood of the Sun, but because of their low luminosity, individual red dwarfs cannot easily be observed.

Commenting on the discovery of Wolf 1061c, Professor Chris Tinney said:

“Our team has developed a new technique that improves the analysis of the data from this precise, purpose-built, planet-hunting instrument, and we have studied more than a decade’s worth of observations of Wolf 1061. These three planets right next door to us join the small but growing ranks of potentially habitable rocky worlds orbiting nearby stars cooler than our sun.”

NASA officially starts program to look for alien life

Just after NASA researchers made the bold claim that they will find alien life in less than 20 years, the space agency has officially launched a project to look for it. The Nexus for Exoplanet System Science, or “NExSS” will be a project integrating several fields of science, aiming to better understand exoplanets with the potential to host life, as well as planet-life interactions.

An image charge with symbolism: the search for life beyond our solar system requires unprecedented cooperation across scientific disciplines. NASA’s NExSS collaboration includes those who study Earth as a life-bearing planet (lower right), those researching the diversity of solar system planets (left), and those on the new frontier, discovering worlds orbiting other stars in the galaxy (upper right).
Credits: NASA

“This interdisciplinary endeavor connects top research teams and provides a synthesized approach in the search for planets with the greatest potential for signs of life,” says Jim Green, NASA’s Director of Planetary Science. “The hunt for exoplanets is not only a priority for astronomers, it’s of keen interest to planetary and climate scientists as well.”

The study of exoplanets is a relatively new field, but has blossomed incredibly in recent years. The first exoplanet was discovered only in 1995, but in the last six years alone, we’ve managed to find over 1,000 exoplanets with thousands of additional candidates waiting to be found. Scientists are working on establishing not only the ‘Goldilocks area‘, in which planets might hold liquid water, but also the search for biosignatures, or signs of life.

Of course, in order to do this, astronomy is simply not enough – you need to understand how the chemistry and geology of an exoplanet might interact with biology, and what visible signals they give out. James Graham, a UC Berkeley professor of astronomy, and leader of the Berkeley/Stanford team explains that the project will bring together researchers from several fields.

“We’re combining techniques to discover new information about how planets form, their range of properties and what sorts of planets are most common, with the eventual goal of finding terrestrial planets and venues for life in the universe,” Graham said.

NExSS will tap into the collective expertise from each of the science communities supported by NASA’s Science Mission Directorate:

  • Earth scientists develop a systems science approach by studying our home planet.
  • Planetary scientists apply systems science to a wide variety of worlds within our solar system.
  • Heliophysicists add another layer to this systems science approach, looking in detail at how the Sun interacts with orbiting planets.
  • Astrophysicists provide data on the exoplanets and host stars for the application of this systems science framework.

The Yale University team, headed by Debra Fischer, will design new spectrometers with the stability to reach Earth-detecting precision for nearby stars. The team will also make improvements to Planet Hunters, www.planethunters.org, a web interface that allows citizen scientists to search for transiting planets in the NASA Kepler public archive data. Meanwhile, a group led by Neal Turner at NASA’s Jet Propulsion Laboratory, California Institute of Technology, will work to understand why so many exoplanets orbit close to their stars. A team at the University of Wyoming, headed by Hannah Jang-Condell, will explore the evolution of planet formation while a Penn State University team, led by Eric Ford, will strive to further understand planetary formation by investigating the bulk properties of small transiting planets and implications for their formation.

The entire thing will be coordinated by Natalie Batalha of NASA’s Ames Research Center, Dawn Gelino with NExScI, the NASA Exoplanet Science Institute, and Anthony del Genio of NASA’s Goddard Institute for Space Studies. All in all, researchers from ten universities will participate.

All in all, it’s a huge thing, with huge potential implications; it may finally help us understand whether or not we are alone in the galaxy.

Source: NASA.

Most stars might hold habitable planets, researchers calculate

According to Danish and Australian researchers who used an improved version of a 250-year old theory, there are billions of the stars in the Milky Way located in the “habitable zone”, where liquid water might exist, and with it, life as we know it.

An old law, revisited

Planets outside our solar system are called exoplanets. The Kepler satellite observes exoplanets by measuring the light curve of a star. When a planet moves in front of the star there is a small dip in brightness. If this little dip in brightness occurs regularly, there might be a planet orbiting the star and obscuring its light.  Image credits: ESO.

Planets outside our solar system are called exoplanets. The Kepler satellite observes exoplanets by measuring the light curve of a star. When a planet moves in front of the star there is a small dip in brightness. If this little dip in brightness occurs regularly, there might be a planet orbiting the star and obscuring its light. Image credits: ESO.

Using the Kepler telescope, astronomers have discovered over a thousand exoplanets in our galaxy. Most of the planetary systems discovered have 2-6 planets, but because Kepler is only suitable for discovering planets near their star, many others might lie undiscovered. When you’re working on scales this big, it mostly becomes a matter of statistics, so researchers from the Australian National University and the Niels Bohr Institute in Copenhagen wanted to calculate the probability for the number of stars in the Milky Way that might have planets in the habitable zone, using what Kepler found as a sample size.

“The motivation was the large sample of multiplanet systems with the Kepler mission (there are hundreds of multiplanet systems) and we wanted to do some statistics with them. Since previous research had indicated that the TB-relation may hold to some degree for some exoplanet systems, we decided to use it for planet predictions,” lead author Steffen Kjær Jacobsen told ZME Science in an email.

According to their calculations, the number of potentially habitable planets is much larger than previously believed, ranging in the billions.

In order to reach this conclusion, they used a newer and improved version of a 250-year-old method called the Titius-Bode law. The Titius-Bode law correctly predicted the orbits of Ceres and Uranus in 1770, much before they were actually discovered, but it actually failed to predict Neptune’s orbit. The law states that there is a certain ratio between the orbital periods of planets in a solar system, so the ratio between the orbital period of the 1st and 2nd planet is more or less the same as the ratio between the 2nd and the 3rd, and so on. But the original law was obviously flawed, so they had to tweak it to work.

“In the new research we are using a generalised version (formulated back in 1965) of the TB-law. This generalized version is more consistent in its application to other systems. There is a small difference in the position of the innermost planets between this generalized version and the first TB relation formulated in the late 1700s. Most importantly, the TB-relation is an empirical law based on observation, so there is no absolute way to derive it. Therefore you will sometimes see people using slightly different versions of it. But, they all predict logarithmic spacings between the planets in a system, which can be used to predict ‘missing’ planets in this planet-position pattern.”

Therefore, if you knew the orbit of an outer and an inner planet, you could potentially calculate the orbit of intermediary planets and see where they lie and if they fit the theory. Empirically, you could determine where other plants “have to be”, according to the T-B law.


The non-revisited version of the T-B law successfully predicted the orbit of some planets in our solar system, but failed on the outer ones. Note that if Neptune is ‘skipped,’ the T-B rule’s distance of 38.8 is quite close to Pluto’s real distance with an error of only 1.62%. Image credits: Wiki Commons.

“We decided to use this method to calculate the potential planetary positions in 151 planetary systems, where the Kepler satellite had found between 3 and 6 planets. In 124 of the planetary systems, the Titius-Bode law fit with the position of the planets. Using T-B’s law we tried to predict where there could be more planets further out in the planetary systems. But we only made calculations for planets where there is a good chance that you can see them with the Kepler satellite,” explains Jacobsen, PhD student in the research group Astrophysics and Planetary Science at the Niels Bohr Institute at the University of Copenhagen.

In the rest 27 out of the 151 planets, the observations didn’t actually agree with the T-B law, so they tried to include more planets, like pieces in a jigsaw puzzle, to see if they could make it fit. They tried to find a pattern and “add” the missing planets to see if this could explain the matter. With this method, they actually predicted a total of 228 new planets; if further observations would actually confirm the existence of these planets, it would not only confirm their idea, but might have huge implications for the discovery of new planets.

“We then made a priority list with 77 planets in 40 planetary systems to focus on because they have a high probability of making a transit, so you can see them with Kepler. We have encouraged other researchers to look for these. If they are found, it is an indication that the theory stands up,” explains Steffen Kjær Jacobsen.

There is still some controversy to this method; as Jacobsen admits, most astronomers wouldn’t rely on this type of results but so far, the theory still stands.

“This is still a pretty controversial subject, whether or not the TB-law can be applied to planetary systems, and my team is probably in the minority of people who believe that it has some merit – that is, there is tendency for systems to adhere to the TB-law to a greater or lesser extent. But we do not expect that all systems will obey TB’s law. Among other things, it depends on the formation history of the system. 124 of the systems adhered better to the generalised TB-relation than our own solar system (this was our criteria for whether the system fitted the TB-relation or not).”

Habitable Planets

Image converted using ifftoany

The illustration shows the habitable zone for different types of stars. The distance to the habitable zone is dependent on how big and bright the star is. The green area is the habitable zone (HZ), where liquid water can exist on a planet’s surface. The red area is too hot for liquid water on the planetary surface and the blue area is too cold for liquid water on the planetary surface. (Credit: NASA, Kepler)


In order for planets to be even considered habitable, they need to be able to host liquid water – this means that they have to not be close enough to their star that everything is scorched, but not far away that everything is frozen. The planet has to be in the perfect sweet spot – the so-called Goldilocks area. But it should be kept in mind that even if the planet is in the Goldilocks area, it doesn’t mean that it does have water, but only that it might have water – there are other factors worth considering, such as the existence of the atmosphere. Still, being in the habitable area is the first step.

The researchers wanted to see how many planets might be in that area, statistically. They found that in the 151 studied planetary systems, there were on average 1-3 planets in the habitable zone for each planetary system. While 151 is a very small sample size considering the size of the galaxy, it’s as good a starting point as any – and if the numbers stand up for the rest of the galaxy, then the Milky Way likely hosts billions of potentially habitable planets – yikes!


Astronomers confirm the existence of potentially habitable super-Earth

Exoplanet GJ581d is the first potentially habitable world astronomers have discovered, but some astronomers believed that the planet wasn’t actually there – it was all an observational flaw mixed with some noise in the signal. However, British researchers recently released a study which confirms that the planet does exist and further underline the matter of habitability. This is one of the planets outside our solar system most likely to harbor life.

Artist’s Impression Of Gliese 581 Planetary System. Image via NSF.

Leading author of the paper, Dr Guillem Anglada-Escudé, said:

“There are always discussions among scientists about the ways we interpret data but I’m confident that GJ 581d has been in orbit around Gliese 581 all along. In any case, the strength of their statement was way too strong. If they way to treat the data had been right, then some planet search projects at several ground-based observatories would need to be significantly revised as they are all aiming to detect even smaller planets. One needs to be more careful with these kind of claims”

The star Gliese 581 is a red dwarf about 20 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun and research suggests that three planets orbit it – one being Gliese 581d. The importance of this planet is double fold:

“The existence (or not) of GJ 581d is significant because it was the first Earth-like planet discovered in the ‘Goldilocks’-zone around another star and it is a benchmark case for the Doppler technique.”

The so-called ‘Goldilocks’ area (more technically called the circumstellar habitable zone (CHZ), or simply the habitable zone) is the region around a star within which planetary-mass objects with sufficient atmospheric pressure can support liquid water at their surfaces – in other words, it’s the area around a star in which we would expect to find life (at least life as we know it).

The planet GJ 581d is likely a super-Earth, much like our Earth except much larger, but that doesn’t reduce its chances of hosting life. However, we are still not able to confirm or infirm this – and unfortunately, we won’t be anytime soon. But in time, as astronomers continue to discover more and more potentially habitable planets, the chance of discovering extraterrestrial life seems to grow more and more.

Journal Reference: Paul Robertson, Suvrath Mahadevan, Michael Endl, Arpita Roy. Response to Comment on “Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581”. DOI: 10.1126/science.1260974

NASA reports the first Earth-sized Exoplanet in the Habitable Zone

Artist’s rendition of Kepler-186f – just 10% larger than Earth.

Remember a few days ago, when I was telling you about the big conference NASA had planned for today? Well, they sure didn’t disappoint! The team of astrophysicists from the SETI Institute and NASA’s Ames Research Center have just reported a major milestone: for the first time, they have found an Earth-sized planet at the right distance from its star – right enough to potentially sustain water, in the so-called habitable zone.

“This is a historic discovery,” says Geoff Marcy, an astronomer at the University of California, Berkeley who was not involved in the research, “it’s the best case for a habitable planet yet found.”

The discovery was made using the Kepler telescope, and it crowns a myriad of valuable findings obtained with the device.  The Kepler telescope tracked roughly 150,000 stars in a small patch of sky, searching for stars that dim at regular intervals as planets pass in front of them; Sadly, the telescope is crippled now, but even though it’s not active  astronomers still comb through the data, finding awesome things like this.

The planet, Kepler-186f is almost the same size as the Earth – just 10% bigger. It rotates a red dwarf star (M dwarf), one roughly half the size of our sun, but close enough to compensate for that difference. It orbits its star every 130 days, and inhabits the chillier end of its star’s habitable zone.

“The temperature on the planet is likely cool, similar to dawn or dusk on a spring day,” Marcy says.

More than 70% of all the planets in the Milky Way Galaxy are red M-dwarfs, and that sheer abundance makes them good targets for uncovering Earth-like planets.

“If we’re going to find any signs of life in the next few decades, it will most likely will be a planet in the habitable zone of an M-dwarf,” says Quintana.

In case you’re not familiar with the term, the habitable zone, colloquially known as the Goldilocks zone, is the area around a star where there is sufficient pressure for planets to support liquid water at their surfaces, and the temperature is just right for water to exist in its liquid form – not evaporating, and not freezing. Life as we know it cannot exist without liquid water.

“We definitely think it’s one step closer to finding a true Sun–Earth analogue,” says study co-author Elisa Quintana, an astronomer at the SETI Institute in Mountain View, California, and at the nearby NASA Ames Research Center in Moffett Field.

It’s different enough to call it a cousin more than a brother, but the two planets definitely have some similarities, but there’s still a lot astrophysicists have to figure out about it. The main argument against life on its surface would be that anything living on Kepler-186f would have to withstand large doses of radiation from its star; to clarify things a little bit: the planet is in the habitable area, which means that might support water, which means that it might have or at least support life.

“We can say it’s probably rocky,” says Tom Barclay, an astrophysicist with the NASA Ames Research Center team. “And because the planet is closer to its star, its days are likely much longer than those on Earth.” As for the planet’s atmosphere, composition, and whether it harbors liquid water, nobody can say. “And it’s important to note that just because this planet is in the habitable zone—that it could support water—that doesn’t mean that it is habitable,” he says.

There are still many variables which come into play, and while astronomers are excited about this, they still have many questions.

“Things have to line up just right,” Coughlin says, “so when we do find something exciting like this planet, that tells us that there’s a lot more out there. We’ve found one, but that means there’s hundreds more.”

Still, while this planet may or may not support life, it’s the best chance we’ve got so far – at leasat outside of our solar system.