Tag Archives: habitable zone

15 new planets discovered — one is potentially habitable

A team of Japanese researchers has confirmed the discovery of 15 new exoplanets, orbiting around red dwarfs — including a system of three super-Earths, one of which appears to be located in the star’s habitable zone.

Artistic depiction of exoplanets. Image credits: NASA.

In 1992, two radio astronomers reported the discovery of the first known exoplanet outside our solar system. Since those early days, our hunt for exoplanets — planets orbiting a star other than our Sun — has progressed tremendously, with NASA’s latest count confirming 3,706 exoplanets, and many more candidates awaiting further scrutiny. Now, we can add 15 more to that count.

The findings (published in two papers in The Astronomical Journal) are based on data from NASA Kepler spacecraft’s second mission, K2. All of them orbit stars called red dwarfs, small and relatively cool stars. This is noteworthy because finding a planet around such a low luminosity star is much more challenging than finding a similar planet around a brighter star, like our Sun.

“It’s important to note that the number of planets around red dwarfs is much smaller than the number around solar-type stars,” says Teruyuki Hirano of Tokyo Institute of Technology’s Department of Earth and Planetary Sciences. “Red dwarf systems, especially coolest red dwarfs, are just beginning to be investigated, so they are very exciting targets for future exoplanet research.”

Image Credits: Tokyo Institute of Technology.

Three of the newly-discovered planets are so-called super-Earths, planets with a mass between 1.5 and 2 Earth masses. The term refers only to the mass of the planet and does not imply anything about the surface conditions or habitability. Out of these three, one (K2-155d, with a radius 1.6 times that of Earth) is apparently in the so-called habitable or Goldilocks zone, orbiting its star at just the right distance to be able to support liquid water. However, there’s no guarantee that this is actually the case, as several other parameters can influence a planet’s temperature. Hirano says, “In our simulations, the atmosphere and the composition of the planet were assumed to be Earth-like, and there’s no guarantee that this is the case.”

However, it’s encouraging that these planets were discovered around metal-rich stars, just as previous research predicted. There seems to be a connection between the size of the planets and the amount of metal in the host star.

“Large planets are only discovered around metal-rich stars,” says Teruyuki Hirano, lead researcher of the team. “And what we found was consistent with our predictions. The few planets with a radius about three times that of Earth were found orbiting the most metal-rich red dwarfs.”

Researchers now want to carry out a more precise estimate of the radius and temperature of K2-155 star, around which the three super-Earths orbit, in order to definitely conclude whether K2-155d is habitable. However, achieving this precision requires a different approach, using techniques like interferometry.

The research was published in two articles in The Astronomical Journal.

New research shows that the TRAPPIST-1 planets are even more Earth-like than we thought

Researchers from Bern University have performed the most accurate calculation of the density of the seven planets around the star TRAPPIST-1, making them the best-studied planets outside our own solar system. They found that all the planets are rocky and contain 5% water — much more than what Earth has.

An artistic depiction of what the seven planets might look like, based on available information about their size, density, and distance to the star. Credits: NASA/JPL/Caltech.

TRAPPIST-1, also technically designated as 2MASS J23062928-0502285, is a seemingly inconspicuous ultra-cool red dwarf star. However, astronomers have taken a special interest in it, as it seemingly harbors seven Earth-like planets, several of which have the potential to host life. Now, a new study offers an unprecedented view into the physical and chemical characteristics of these planets.

In order to assess their density, astronomers took advantage of something called “transit timing variations,” a method which has also been used to detect planets. Essentially, when a planet passes in front of a star, it causes a dip in luminosity. By studying that dip, you can identify a planet and its size. But astronomers went even deeper.

The TRAPPIST planets are located very close to each other — if you had an observer on one of them, they’d have a pretty awesome view of at least a couple other planets. But this also means that they attract each other gravitationally. If a single planet were to rotate around the star, or if the planets were too far apart for gravity to make a significant difference, a planet would always cross in front of its host star at consistent intervals of time. But because they’re so closely packed, they change the timing of each other’s “years” ever so slightly. This allowed astronomers to deduce the mass of the planets with an uncertainty less than 10%, and with the size and the mass, they calculated the density.

“We now know more about TRAPPIST-1 than any other planetary system apart from our own,” said Sean Carey, manager of the Spitzer Science Center at Caltech/IPAC in Pasadena, California, and co-author of the new study. “The improved densities in our study dramatically refine our understanding of the nature of these mysterious worlds.”

But while the planets might be similar to Earth, TRAPPIST-1 is extremely small by stellar standards, being only 9 percent as massive as our Sun. In turn, this means that it’s much cooler than our star, and in order for the planets to have Earth-like temperatures, they’d first need to be much closer to the star. This has indeed been confirmed by observation, as several of the planets lie closer to TRAPPIST-1 than Mercury to the Sun. In fact, a couple of them are actually much more illuminated than the Earth, while another planet, Trappist-d, matches Earth near-perfectly in terms of illumination.

This graph presents known properties of the seven TRAPPIST-1 exoplanets (labeled b through h), showing how they compare to the inner rocky worlds in our own solar system. Credit: NASA/JPL-Caltech.

The fact that the planets have up to 5% water is also an intriguing sign, especially considering that on Earth, water accounts for only 0.02% of the planet’s mass.

However, just because these planets have the right density, structure, and distance from their star, doesn’t make them habitable. It makes them potentially habitable, which is a big distinction.

“Densities, while important clues to the planets’ compositions, do not say anything about habitability. However, our study is an important step forward as we continue to explore whether these planets could support life,” said Brice-Olivier Demory, co-author at the University of Bern.

This illustration shows the seven Earth-size planets of TRAPPIST-1. The image does not show the planets’ orbits to scale, but highlights possibilities for how the surfaces of these intriguing worlds might look. Credit: NASA/JPL-Caltech.

For instance, we have no idea how their surfaces might look like. Mars and the Moon have quite similar densities, but they look completely different. It’s tantalizing to think what the surface of these planets might be like, but for now, we just don’t have enough information to make any assumption. The next step will be using NASA’s James Webb Space Telescope to figure out whether these planets have atmospheres and if yes, what these atmospheres are like.

“Our conceptions of what these planets look like today may change dramatically over time,” said Robert Hurt, senior visualization scientist at the Spitzer Science Center. “As we learn more about these planets, the pictures we make will evolve in response to our improved understanding.

Journal Reference: S. Grimm et al.: The nature of the TRAPPIST-1 exoplanets, Astronomy and Astrophysics, 05.02.2018, in press.

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’s exciting announcement: They’ve discovered an Earth-like planet in the habitable zone

Planet Kepler-452b: the first near-Earth-size world to be found in the habitable zone of a star that is similar to our Sun. This extremely exciting announcement was made by NASA today; while this doesn’t mean that the planet is inhabited, it does mean that it has many of the characteristics that our own Earth-Sun system has, and the odds of it hosting life seem significant.

The sweep of NASA Kepler mission’s search for small, habitable planets in the last six years. The first planet smaller than Earth, Kepler-20e, was discovered in December 2011 orbiting a Sun-like star slightly cooler and smaller than our sun every six days. But it is scorching hot and unable to maintain an atmosphere or a liquid water ocean. Kepler-22b was announced in the same month, as the first planet in the habitable zone of a sun-like star, but is more than twice the size of Earth and therefore unlikely to have a solid surface. Kepler-186f was discovered in April 2014 and is the first Earth-size planet found in the habitable zone of a small, cool M dwarf about half the size and mass of our sun. Kepler-452b is the first near-Earth-Size planet in the habitable zone of a star very similar to the sun.
Credits: NASA Ames/W. Stenzel

The first exoplanet orbiting another star like our sun was discovered in 1995; it seems almost incredible to think that just 21 years ago, exoplanets, especially Earth-like planets, were science fiction. Today, thousands of discoveries later, we know better.

The Kepler-452 system is located 1,400 light-years away in the constellation Cygnus, but the planet itself is quite old – 6 billion years old, 1.5 billion years older than our sun. While Kepler-452b is larger than Earth, its 385-day orbit is only 5 percent longer, and the planet is just 5% farther away from its star than the Earth is from the Sun.

“The discovery of Kepler-186f is a significant step toward finding worlds like our planet Earth,” said Paul Hertz, NASA’s Astrophysics Division director at the agency’s headquarters in Washington. “Future NASA missions, like the Transiting Exoplanet Survey Satellite and the James Webb Space Telescope, will discover the nearest rocky exoplanets and determine their composition and atmospheric conditions, continuing humankind’s quest to find truly Earth-like worlds.”

Its size is also known – Kepler-452b is 60 percent larger in diameter than Earth, being considered a “super Earth”. It’s a rocky planet just like Earth, but we don’t yet know its composition. What we do know is that while bigger, Kepler-452b has a 385-day orbit, only 5 percent longer than ours.

“We know of just one planet where life exists — Earth. When we search for life outside our solar system we focus on finding planets with characteristics that mimic that of Earth,” said Elisa Quintana, research scientist at the SETI Institute at NASA’s Ames Research Center in Moffett Field, Calif., and lead author of the paper published today in the journal Science. “Finding a habitable zone planet comparable to Earth in size is a major step forward.”

This artist’s concept depicts one possible appearance of the planet Kepler-452b, the first near-Earth-size world to be found in the habitable zone of star that is similar to our sun. The habitable zone is a region around a star where temperatures are right for water — an essential ingredient for life as we know it — to pool on the surface. Credits: NASA Ames/JPL-Caltech/T. Pyle

But as exciting as this announcement is, it’s important to remember that there is no clear indication that the planet might host life. We know nothing of the temperature and (potential) atmosphere of the planet, and these are decisive factors. It’s these two that will determine whether or not this is a true Earth twin, or only a distant cousin.

“Being in the habitable zone does not mean we know this planet is habitable. The temperature on the planet is strongly dependent on what kind of atmosphere the planet has,” said Thomas Barclay, research scientist at the Bay Area Environmental Research Institute at Ames, and co-author of the paper. “Kepler-186f can be thought of as an Earth-cousin rather than an Earth-twin. It has many properties that resemble Earth.”

But even finding a “cousin” of Earth is still remarkable, especially when you consider where we’ve come in 25 years; one can only wonder, where will we be another 25 years from now?

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!


The habitable zone

Newfound Planet ‘Gliese 832c’ May Be Able To Support Life

A newfound alien planet located “just” 16 light years away from Earth might be able to support life, a new study has shown.

The habitable zone

The habitable zone

To get some perspective, the Milky Way is approximately 100,000 light-years across. The closest planet to our solar system is Proxima Centauri – 4.2 light-years away. A recent study concluded that there are likely billions of Earth-like planets in the Milky Way, but few of them are this close to us.

Gliese 832c is a “super-Earth” – a rocky planet just like the one we live on, and but 5 times more massive. It lies much closer to its star than Earth from the Sun – it takes it just 36 days to make one full orbit around its star; however, because it orbits a much cooler red dwarf, Gliese 832c receives about as much energy as Earth does. Interestingly enough, despite all these differences, in a way, it’s very much like Earth.

“The Earth Similarity Index (ESI) of Gliese 832c (ESI = 0.81) is comparable to Gliese 667Cc (ESI = 0.84) and Kepler-62e (ESI = 0.83),” Mendez wrote in a blog post today (June 25). (A perfect “Earth twin” would have an ESI of 1.). This makes Gliese 832c one of the top three most Earth-like planets according to the ESI (i.e., with respect to Earth’s stellar flux and mass) and the closest one to Earth of all three — a prime object for follow-up observations,” he added.

Astronomers found this using a rather common technique in the field: they observe the tiny wobbles the planet’s gravity induces in the motion of its host star. They then used only three separate instruments to find out the planet’s location and mass: a Spectrograph on the Anglo-Australian Telescope in Australia, the Carnegie Planet Finder Spectrograph on the Magellan II telescope in Chile and the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph, also located in Chile.

Gliese 832c is actually the second planet to be found in its solar system, with the previous one, Gliese 832b found in 2009. However, that one looks more like Jupiter than Earth.

“So far, the two planets of Gliese 832 are a scaled-down version of our own solar system, with an inner, potentially Earth-like planet and an outer, Jupiter-like giant planet,” Mendez wrote.

The habitable zone, also called the “Goldilocks area” is the sweet spot – the distance from a star at which a planet receives just enough energy to be able to potentially sustain life. However, just because a planet is in the habitable zone doesn’t mean it actually has life. That would be a huge stretch, and it is not one that should be made yet, with any announcement of this type.

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.


1 in 5 stars may have Earth-sized planets

A statistical analysis of observations based on the Kepler telescope indicates that 20 percent of all stars in the Milky Way host earth-sized planets, a significant part of which could potentially be habitable.

Habitable planets in the Milky Way

NASA’s Kepler telescope is crippled – it’s reached the end of its four year mission, but it provided an immense amount of useful data for astronomers who want to find out just how many Earth-like planets are in our galaxy. Given that 1 in 5 planets have are rather similar in size to our own, it seems safe to assume that at least a big part of them are also in the habitable area.

“When you look up at the thousands of stars in the night sky, the nearest sun-like star with an Earth-size planet in its habitable zone is probably only 12 light years away and can be seen with the naked eye. That is amazing,” said UC Berkeley graduate student Erik Petigura, who led the analysis of the Kepler data.

Exoplanet discovery is a field that has advanced exponentially. The first exoplanet was discovered in 1989, and until 1992, two others were announced. However, it took 3 more years before another was reported, and in early 2005, less than 15 exoplanets had been discovered. As of 1 November 2013, a total of 1038 confirmed exoplanets are listed in the Extrasolar Planets Encyclopaedia, including a few that were confirmations of controversial claims from the late 1980s.

“It’s been nearly 20 years since the discovery of the first extrasolar planet around a normal star. Since then, we have learned that most stars have planets of some size orbiting them, and that Earth-size planets are relatively common in close-in orbits that are too hot for life,” said Andrew Howard, a former UC Berkeley post-doctoral fellow who is now on the faculty of the Institute for Astronomy at the University of Hawaii. “With this result, we’ve come home, in a sense, by showing that planets like our Earth are relatively common throughout the Milky Way Galaxy.”

Earth-sized does not mean habitable

habitable zone

Currently, astronomers have a pretty volatile definition for what ‘habitable’ means – as I told you in this article. Planetary habitability is the measure of a planet’s or a natural satellite’s potential to develop and sustain life – basically, at the moment, it is a measure of how much a planet features the same conditions as Earth, because right now, those are the only ones that we know for sure can sustain life. In determining the habitability potential of a body, researchers estimate its density, mass, distance from its star, size of the star, orbital properties, atmosphere, and potential chemical interactions. The possibility of so many Earth-sized planets existing is absolutely thrilling, even though a big portion of them are not habitable.

“For NASA, this discovery is really important, because future missions will try to take an actual picture of a planet, and the size of the telescope they have to build depends on how close the nearest Earth-size planets are,” Howard said. “An abundance of planets orbiting nearby stars simplifies such follow-up missions.”

Even if a planet is similar in size to Earth, and even if it lies in the habitable zone, where it’s not too hot and not to o cold, that doesn’t mean that it has life.

“Some may have thick atmospheres, making it so hot at the surface that DNA-like molecules would not survive. Others may have rocky surfaces that could harbor liquid water suitable for living organisms,” Marcy said. “We don’t know what range of planet types and their environments are suitable for life.”

However, good news also came from Howard, Marcy and their colleagues reported that one Earth-size planet discovered by Kepler — albeit, a planet with a likely temperature of 2,000 Kelvin, which is far too hot for life as we know it — is the same density as Earth and most likely composed of rock and iron, like Earth.

“This gives us some confidence that when we look out into the habitable zone, the planets Erik is describing may be Earth-size, rocky planets,” Howard said.

New ‘Habitable Zone’ for alien planets redefined

As our search for alien planets improves and intensifies, astronomers are starting to pay more and more attention to one crucial aspect of alien planets:  whether they fit into the ‘habitable zone‘ – the so-called Goldilocks area in which a planet is not too close and not too far from its star – just perfectly placed to support liquid life, which is the basis of life as we know it.

The old definition of the habitable zone. According to the new one, Mars falls just inside it - highlighting the difference between astronomic and geologic habitability.

The old definition of the habitable zone. According to the new one, Mars falls just inside it – highlighting the difference between astronomic and geologic habitability.

Of course non-carbon based life could exist in a solvent different to water, but so far, astronomers are focusing on whatever signals they can detect. Now, they have redefined the borders for this area, potentially kicking out some exoplanaets that were thought to fall within it, but on the other hand, maybe adding some new ones.

“This will have a significant impact on the number of exoplanets that are within habitable zone,” said research team leader Ravi Kumar Kopparapu of Penn State University.

The new definition of the habitable zone takes into consideration updated atmospheric databases – HITRAN (high-resolution transmission molecular absorption) and HITEMP (high-temperature spectroscopic absorption parameters), which give the absorbtion parameters of both water and carbon dioxide, two properties important for the planets’ atmosphere, significantly influencing their capability to host water.

However, scientists warn, this still doesn’t take into consideration feedback effects from clouds, which will also affect a planet’s habitability. Also, there is a difference between what habitable means from an astronomic point of view, and from a geologic point of view.

The previous definition of the habitable zone was derived about 20 years ago by Penn State researcher James Kasting, who also worked to conduct these updates.

“At the time when he wrote that paper no exoplanets were discovered,” Kopparapu explained. “In 20 years, hundreds, maybe thousands have been discovered.” – which makes his initial work all the more admirable, but it also means changes are necessary.

The new changes aren’t dramatic; considering an Astronomical Unit (AU) as the distance between the Earth and the Sun, the limits for the habitable zone have been changed from between 0.95 and 1.67 AU to 0.99 AU to 1.7 AU. Even so, this slight change will probably have significant consequences.

“It’s a surprise that Earth is so close to the inner edge of the habitable zone,” said astronomer Abel Méndez of the University of Puerto Rico at Arecibo, who was not part of the team behind the redefinition.

He mentioned one planet in particular, Gliese 581d, was thought to lie at the outer edge of its star’s habitable zone – with the new definition, Gliese 581d falls exactly in the middle, making it an even better candidate.

“That will be a big change for that particular planet,” Méndez said. “That means the prospects for life on the planet will be much better.”

The changes will be published in the future edition of the Astrophysical Journal.

You can browse the catalog of Habitable Planets directly here.

Newest found planet is just the right temperature for life

The race for finding habitable planets outside our solar system is definitely heating up. After we told you about Gliese, a planet which seems habitable enough, researchers have reported finding yet another planet, which is not too hot and not too cold either – Kepler-22b is just the right temperature for life as we know it: 72 degrees, a perfect spring temperature on Earth.

Found by the Kepler space telescope (like many other interesting planets), Kepler-22b is the best candidate so far for life outside the solar system – in fact, it might very well be the best candidate for life in our solar system as well (Earth aside).

“If it has a surface, it ought to have a nice temperature,” said Kepler’s lead scientist, Bill Borucki, during a teleconference Monday.

Furthermore, it is located exactly in the habitable area researchers have talked about for so long – not too close and not too far from its star.

“It’s right in the middle of the habitable zone,” said Natalie Batahla, a Kepler scientist, referring to the narrow, balmy band of space around any star where water can be liquid. “The other exciting thing is that it orbits a star very, very similar to our own sun.”

However, there is still a pretty big ‘if’, regarding the planet’s atmosphere. Its temperature and living conditions pretty much depend on its atmosphere, which acts like a blanket and heats the planet. However, even without atmosphere, it is probably hot enough to bear liquid water on its surface.

It’s 2.4 times bigger than our own Earth, but its composition is still somewhat a mystery. It could very well be a rocky planet, like our own planet and Mars for example, and it could also be gaseous, like Jupiter or Uranus. Even more, it could also be a water planet, covered by deep oceans from one end to another – and this is an extremely interesting and provoking scenario. Just imagine, a world 2.4 times bigger than the Earth, covered with deep oceans, at spring temperature – bearing life is extremely likely.

Determining its composition is done by determining its mass, which is something the Kepler telescope can’t measure that; the good news is – Earth located telescopes can. They can estimate the tug and pull it exerts on other bodies and thus accurately estimate its mass. Telescopes in Hawaii, Chile, and all over the world are on it in this very moment.

Besides its temperature, Kepler-22b, which is located 600 light years away from us, shares other intriguing similarities with Earth. Its planet is like the Sun’s twin – the light hitting the planet has the same colour as the light hitting Earth, and its year is also comparable to ours: 290 days instead of 365.

Finding Kepler-22b was an admirable achievement, but it also required a bit of luck – but the luck came in time, right before Christmas.

“It’s a great gift,” said Borucki. “We consider it our sort of Christmas planet.”

Researchers working at the Kepler project claim Kepler-22b is a far better candidate for life than another planet found by the European planet-hunting project in September. The planet in case, called HD85512b circles a star which somewhat resembles the Sun, but is smaller and cooler. It is also on the edge of the habitable zone, which means that any water on its surface is likely to be ice.

Astrophysicists are absolutely thrilled by the Kepler-22b discovery, as it shows once again the $600 million Kepler mission which launched in 2009 is more than worth it. The mission has the purpose of finding other Earth-like planets, and in general, planets bearing life. This week, researchers got together to estimate the success or lack of it they’ve had so far – everybody was pleased.

“We are getting really close, we are really homing in on the true Earth-sized habitable planets.”

So far, Kepler’s numbers are absolutely fascinating: out of 150.000 scanned stars, it found 2,326 “candidate planets”. Most of them are gas giants, like Jupiter. But some, 207 including Kepler-22b are comparable in size to Earth. Follow up observations and studies will determine if these planets indeed have the potential to bear life.

“We won’t know if they’re there unless we look,” Tarter said before referencing the 1997 film “Contact.” Jodie Foster played the role of Tarter in the movie, listening to stars that have “just right” planets circling them before striking the alien jackpot. “Just like Jodie Foster … in ‘Contact,’ we will give higher priority to planets that our colleagues tell us are not too warm, not too cold, but just right.”

Meanwhile, 42 radio telescopes are scanning Kepler-22b and other candidates, in the hope of finding the first extrasolar planet which bears life.