Could the Closest Extrasolar Planet Be Habitable? Astronomers Plan to Find Out

The extra-solar planet known as Proxima b has occupied a special place in the public mind ever since its existence was announced in August of 2016. As the closest exoplanet to our Solar System, its discovery has raised questions about the possibility of exploring it in the not-too-distant future. And even more tantalizing are the questions relating to its potential habitability.

Despite numerous studies that have attempted to indicate whether the planet could be suitable for life as we know it, nothing definitive has been produced. Fortunately, a team of astrophysics from the University of Exeter – with the help of meteorology experts from the UK’s Met Office – have taken the first tentative steps towards determining if Proxima b has a habitable climate.

According to their study, which appeared recently in the journal Astronomy & Astrophysics, the team conducted a series of simulations using the state-of-the-art Met Office Unified Model (UM). This numerical model has been used for decades to study Earth’s atmosphere, with applications ranging from weather prediction to the effects of climate change.

Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO

With this model, the team simulated what the climate of Proxima b would be like if it had a similar atmospheric composition to Earth. They also conducted simulations on what the planet would be like it if had a much simpler atmosphere – one composed of nitrogen with trace amounts of carbon dioxide. Last, but not least, they made allowances for variations in the planet’s orbit.

For instance, given the planet’s distance from its sun – 0.05 AU (7.5 million km; 4.66 million mi) – there have been questions about the planet’s orbital characteristics. On the one hand, it could be tidally-locked, where one face is constantly facing towards Proxima Centauri. On the other, the planet could be in a 3:2 orbital resonance with its sun, where it rotates three times on its axis for every two orbits (much like Mercury experiences with our Sun).

In either case, this would result in one side of the planet being exposed to quite a bit of radiation. Given the nature of M-type red dwarf stars, which are highly variable and unstable compared to other types of stars, the sun-facing side would be periodically irradiated.  Also, in both orbital scenarios, the planet would be subject to significant variations in temperature that would make it difficult for liquid water to exist.

For example, on a tidally-locked planet, the main atmospheric gases on the night-facing side would be likely to freeze, which would leave the daylight zone exposed and dry. And on a planet with a 3:2 orbital resonance, a single solar day would most likely last a very long time (a solar day on Mercury lasts 176 Earth days), causing one side to become too hot and dry the other side too cold and dry.

This infographic compares the orbit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System. Credit: ESO

By taking all this into account, the team’s simulations allowed for some crucial comparisons with previous studies, but also allowed the team to reach beyond them. As Dr. Ian Boutle, an Honorary University Fellow at the University of Exeter and the lead author of the paper, explained in a University press release:

“Our research team looked at a number of different scenarios for the planet’s likely orbital configuration using a set of simulations. As well as examining how the climate would behave if the planet was ‘tidally-locked’ (where one day is the same length as one year), we also looked at how an orbit similar to Mercury, which rotates three times on its axis for every two orbits around the sun (a 3:2 resonance), would affect the environment.”

In the end, the results were quite favorable, as the team found that Proxima b would have a remarkably stable climate with either atmosphere and in either orbital configuration. Essentially, the UM software simulations showed that when both atmospheres and both the tidally-locked and 3:2 resonance configurations were accounted for, there would still be regions on the planet where water was able to exist in liquid form.

Naturally, the 3:2 resonance example resulted in more substantial areas of the planet falling within this temperature range. They also found that an eccentric orbit, where the distance between the planet and Proxima Centauri varied to a significant degree over the course of a single orbital period, would lead to a further increase in potential habitability.

Artist’s depiction of a watery exoplanet orbiting a distant red dwarf star. New research indicates that Proxima b could be especially watery. Credit: CfA

As Dr James Manners, another Honorary University Fellow and one of the co-authors on the paper, said:

“One of the main features that distinguishes this planet from Earth is that the light from its star is mostly in the near infra-red. These frequencies of light interact much more strongly with water vapor and carbon dioxide in the atmosphere which affects the climate that emerges in our model.”

Of course, much more work needs be done before we can truly understand whether this planet is capable of supporting life as we know it. Beyond feeding the hopes of those who would like to see it colonized someday, studies into Proxima b’s conditions are also of extreme importance in determining whether or not indigenous life exists there right now.

But in the meantime, studies such as this are extremely helpful when it comes to anticipating what kinds of environments we might find on distant planets. Dr Nathan Mayne – the scientific lead on exoplanet modelling at the University of Exeter and a co-author on the paper – also indicated that climate studies of this kind could have applications for scientists here at home.

“With the project we have at Exeter we are trying to not only understand the somewhat bewildering diversity of exoplanets being discovered, but also exploit this to hopefully improve our understanding of how our own climate has and will evolve,” he said. What’s more, it helps to illustrate how conditions here on Earth can be used to predict what may exist in extra-solar environments.

While that might sound a bit Earth-centric, it is entirely reasonable to assume that planets in other star systems are subject to processes and mechanics similar to what we’ve seen on the Solar planets. And this is something we are invariably forced to do when it comes to searching for habitable planets and life beyond our Solar System. Until we can go there directly, we will be forced to measure what we don’t know by what we do.

Further Reading: University of Exeter, Astronomy & Astrophysics

Is This The Exoplanet Where Life Will First Be Found?

It is good time to be an exoplanet hunter… or just an exoplanet enthusiast for that matter! Every few weeks, it seems, new discoveries are being announced which present more exciting opportunities for scientific research. But even more exciting is the fact that every new find increases the likelihood of locating a potentially habitable planet (and hence, life) outside of our Solar System.

And with the discovery of LHS 1140b – a super-Earth located approximately 39 light years from Earth – exoplanet hunters think they have found the most likely candidate for habitability to date. Not only does this terrestrial (i.e. rocky) planet orbit within its sun’s habitable zone, but examinations of the planet (using the transit method) have revealed that it appears to have a viable atmosphere.

Credit for the discovery goes to a team of international scientists who used the MEarth-South telescope array – a robotic observatory located on Cerro Tololo in Chile – to spot the planet. This project monitors the brightness of thousands of red dwarf stars with the goal of detecting transiting planets. After consulting data obtained by the array, the team noted characteristic dips in the star’s brightness that indicated that a planet was passing in front of it.

The MEarth-South telescope array, located on Cerro Tololo in Chile, searches for planets by monitoring the brightness of nearby, small stars. Credit: Jonathan Irwin

These findings were then followed up using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument at the ESO’s La Silla Observatory, located on the outskirts of Chile’s Atacama Desert. According to the their study – which appeared in the April 20th, 2017, issue of the journal Nature – the team was able to make estimates of the planet’s age, size, mass, distance from its star, and orbital period.

They estimate that the planet is at least five billion years old – about 500 million years older than Earth. It is also slightly larger than Earth – 1.4 times Earth’s diameter – and is considerably more massive, weighing in at a hefty 6.6 Earth masses. Since they were able to view the planet almost edge-on, the team was also able to determine that it orbits its sun at a distance of about 0.1 AU (one-tenth the distance between Earth and the Sun) with a period of 25 days.

However, since its star is a red dwarf, this proximity places it in the middle of the system’s habitable zone. But what was most exciting was the fact that the team was able to look for evidence of an atmosphere since the planet was passing in front of its star – something that has not been possible with many exoplanets. Because of this, they were able to conduct transmission spectroscopy measurements that revealed the presence of an atmosphere.

As Jason Dittmann – of the Harvard-Smithsonian Center for Astrophysics (CfA) and the lead author of the study – said in a CfA press release:

“This is the most exciting exoplanet I’ve seen in the past decade. We could hardly hope for a better target to perform one of the biggest quests in science — searching for evidence of life beyond Earth.”

This artist’s impression shows the exoplanet LHS 1140b, which orbits a red dwarf star 40 light-years from Earth. Credit: ESO/spaceengine.org

Granted, this exoplanet is not as close as Proxima b, which orbits Proxima Centauri – just 4.243 light years away. And it certainly isn’t as robust a find as the TRAPPIST-1 system, with its seven rocky planets, three of which are located within its habitable zone. But compared to these candidates, the researchers were able to place solid constraints on the planet’s mass and density, not to mention the fact that they were able to observe an atmosphere.

The discovery of an exoplanet that orbits a red dwarf star and has an atmosphere is also encouraging in a wider context. Low-mass red dwarf stars are the most common star in the galaxy, accounting for 75% of stars in our cosmic neighborhood alone. They are also long-lived (up to 10 trillion years), and recent research indicates that they are capable of hosting large numbers of planets.

But given their variability and unstable nature,  astronomers have expressed doubts as to whether or not planet orbiting them could retain their atmospheres for very long. Knowing that a terrestrial planet that orbits a red dwarf, is five billion years old, and still has an atmosphere is therefore a very good sign. But of course, simply knowing there is an atmosphere doesn’t mean that it is conducive to life as we know it.

“Right now we’re just making educated guesses about the content of this planet’s atmosphere,” said Dittman. “Future observations might enable us to detect the atmosphere of a potentially habitable planet for the first time. We plan to search for water, and ultimately molecular oxygen.”

This chart shows the location of the faint red star LHS 1140 in the faint constellation of Cetus (The Sea Monster). This star is orbited by a super-Earth exoplanet called LHS 1140b, which may be best place to look for signs of life beyond the Solar System. The star is too faint to be seen in a small telescope.

Hence, additional studies will be needed before this planet can claim the title of “best place to look for signs of life beyond the Solar System”. To that end, future space-based missions like the James Webb Space Telescope (which will launch in 2018), and ground-based instruments like the Giant Magellan Telescope and the ESO’s Extremely Large Telescope,  will be especially well-suited!

In the meantime, the NASA/ESA Hubble Space Telescope will be conducting observations of the star system in the near future. These observations, it is hoped, will indicate exactly how much high-energy radiation LHS 1140b receives from its sun. This too will go a long way towards determining just how habitable the Super-Earth is.

And be sure to enjoy this video of the LHS 1140 star system, courtesy of the European Southern Observatory and spaceengine.org:

Further Reading: ESO, CfA

Finally! A Low Mass Super-Earth With Some Funky Atmosphere

In 2015, astronomers discovered an intriguing extrasolar planet located in a star system some 39 light years from Earth. Despite orbiting very close to its parent star, this “Venus-like” planet – known as GJ 1138b – appeared to still be cool enough to have an atmosphere. In short order, a debate ensued as to what kind of atmosphere it might have, whether it was a “dry Venus” or a “wet Venus”.

And now, thanks to the efforts of an international team of researchers, the existence of an atmosphere has been confirmed around GJ 1138b. In addition to settling the debate about the nature of this planet, it also marks the first time that an atmosphere has been detected around a low-mass Super-Earth. On top of that, GJ 1138b is now the farthest Earth-like planet that is known to have an atmosphere.

Led by John Southworth (of Keele University) and Luigi Mancini (of the University of Rome Tor Vergata), the research team included members from the Max Planck Institute for Astronomy (MPIA), the National Institute for Astrophysics (INAF), the University of Cambridge and Stockholm University. Their study, titled “Detection of the atmosphere of the 1.6 Earth mass exoplanet GJ 1132b“, recently appeared in The Astrophysical Journal.

Artist’s impression of the “Venus-like” exoplanet GJ 1132b. Credit: cfa.harvard.edu

Using the GROND imager on the La Silla Observatory’s 2.2m ESO/MPG telescope, the team monitored GJ 1132b in different wavelengths as it transited in front of its parent star. Given the planet’s orbital period (1.6 days), these transits happen quite often, which presented plenty of opportunities to view it pass in front of its star. In so doing, they monitored the star for slight decreases in its brightness.

As Dr. Southworth explained to Universe via email, these observations confirmed the existence of an atmosphere:

“What we did was to measure the amount of dimming at 7 different wavelengths in optical and near-infrared light. At one of these wavelengths (IR) the planet seemed to be slightly bigger. This indicated that the planet has a large atmosphere around it which allows most of the starlight to pass through, but is opaque at one wavelength.”

The team members from the University of Cambridge and the MPIA then conducted simulations to see what this atmosphere’s composition could be. Ultimately, they concluded that it most likely has a thick atmosphere that is rich in water and/or methane – which contradicted recent theories that the planet had a thin and tenuous atmosphere (i.e. a “dry Venus”).

The ESO’s Paranal Observatory, located in the Atacama Desert of Chile. Credit: ESO

It was also the first time that an atmosphere has been confirmed around a planet that is not significantly greater in size and mass to Earth. In the past, astronomers have detected atmospheres around many other exoplanets. But in these cases, the planets were either gas giants or planets that were many times Earth’s size and mass (aka. “Super-Earths”). GJ 1132b, however, is 1.6 times as massive as Earth, and measures 1.4 Earth radii.

In addition, these findings are a significant step in the search for life beyond our Solar System. At present, astronomers seek to determine the chemical composition of a planet’s atmosphere to determine if it could be habitable. Where the right combination of chemical imbalances exist, the presence of living organisms is seen as a possible cause.

By being able to determine that a planet at lower end of the super-Earth scale has an atmosphere, we are one step closer to being able to determine exoplanet habitability. The detection of an atmosphere-bearing planet around an M-type (red dwarf) star is also good news in and of itself. Low-mass red dwarf stars are the most common star in the galaxy, and recent findings have indicated that they might be our best shot for finding habitable worlds.

Besides detecting several terrestrial planets around red dwarf stars in recent years – including seven around a single star (TRAPPIST-1) – there is also research that suggests that these stars are capable of hosting large numbers of planets. At the same time, there have been concerns about whether red dwarfs are too variable and unstable to support habitable worlds.

Artist’s impression of Kepler-1649b, the “Venus-like” world orbiting an M-class star 219 light-years from Earth. Credit: Danielle Futselaar

As Southworth explained, spotting an atmosphere around a planet that closely orbits a red dwarf could help bolster the case for red dwarf habitability:

“One of the big issues has been that very-low-mass stars typically have strong magnetic fields and thus throw out a lot of X-ray and ultraviolet light. These high-energy photons tend to destroy molecules in atmospheres, and might also evaporate them completely. The fact that we have detected an atmosphere around GJ 1132b means that this kind of planet is indeed capable of retaining an atmosphere for billions of years, even whilst being bombarded by the high-energy photons from their host stars.

In the future, GJ 1132b is expected to be a high-priority target for study with the Hubble Space Telescope, the Very Large Telescope (VLT) at the Paranal Observatory in Chile, and next-generation telescopes like the James Webb Space Telescope (scheduled for launch in 2018). Already, observations are being made, and the results are being eagerly anticipated.

I’m sure I’m not the only one who would like to hear what astronomers discover as they set their sights on this nearby star system and it’s Venus-like world! In the meantime, be sure to check out this video about GJ 1132b, courtesy of MIT news:

Further Reading: Max Planck Institute for Astronomy

Potentially Habitable Exoplanet Confirmed Around Nearest Star!

For years, astronomers have been observing Proxima Centauri, hoping to see if this red dwarf has a planet or system of planets around it. As the closest stellar neighbor to our Solar System, a planet here would also be our closest planetary neighbor, which would present unique opportunities for research and exploration.

So there was much excitement when, earlier this month, an unnamed source claimed that the ESO had spotted an Earth-sized planet orbiting within the star’s habitable zone. And after weeks of speculation, with anticipation reaching its boiling point, the ESO has confirmed that they have found a rocky exoplanet around Proxima Centauri – known as Proxima b.

Located just 4.25 light years from our Solar System, Proxima Centauri is a red dwarf star that is often considered to be part of a trinary star system – with Alpha Centauri A and B. For some time, astronomers at the ESO have been observing Proxima Centauri, primarily with telescopes at the La Silla Observatory in Chile.

Their interest in this star was partly due to recent research that has shown how other red dwarf stars have planets orbiting them. These include, but are not limited to, TRAPPIST-1, which was shown to have three exoplanets with sizes similar to Earth last year; and Gliese 581, which was shown to have at least three exoplanets in 2007.

The ESO also confirmed that the planet is potentially terrestrial in nature (i.e. rocky), similar in size and mass to Earth, and orbits its star with an orbital period of 11 days. But best of all are the indications that surface temperatures and conditions are likely suitable for the existence of liquid water.

It’s discovery was thanks to the Pale Red Dot campaign, a name which reflects Carl Sagan’s famous reference to the Earth as a “pale blue dot”. As part of this campaign, a team of astronomers led by Guillem Anglada-Escudé – from Queen Mary University of London – have been observing Proxima Centauri for signs of wobble (i.e. the Radial Velocity Method).

After combing the Pale Red Dot data with earlier observations made by the ESO and other observatories, they noted that Proxima Centauri was indeed moving. With a regular period of 11.2 days, the star would vary between approaching Earth at a speed of 5 km an hour (3.1 mph), and then receding from Earth at the same speed.

Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO
Artist’s impression of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri. The double star Alpha Centauri AB is visible to the upper right of Proxima itself. Credit: ESO

This was certainly an exciting result, as it indicated a change in the star’s radial velocity that was consistent with the existence of a planet. Further analysis showed that the planet had a mass at least 1.3 times that of Earth, and that it orbited the star at a distance of about 7 million km (4.35 million mi) – only 5% of the Earth’s distance from the Sun.

The discovery of the planet was made possible by the La Silla’s regular observation of the star, which took place star  between mid-January and April of 2016, using the 3.6-meter telescope‘s HARPS spectrograph. Other telescopes around the world conducted simultaneous observation in order to confirm the results.

One such observatory was the San Pedro de Atacama Celestial Explorations Observatory in Chile, which relied on its ASH2 telescope to monitor the changing brightness of the star during the campaign. This was essential, as red dwarfs like Proxima Centauri are active stars, and can vary in ways that would mimic the presence of the planet.

Guillem Anglada-Escudé described the excitement of the past few months in an ESO press release:

“I kept checking the consistency of the signal every single day during the 60 nights of the Pale Red Dot campaign. The first 10 were promising, the first 20 were consistent with expectations, and at 30 days the result was pretty much definitive, so we started drafting the paper!”

This infographic compares the orbit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System. Proxima Centauri is smaller and cooler than the Sun and the planet orbits much closer to its star than Mercury. As a result it lies well within the habitable zone, where liquid water can exist on the planet’s surface.
Infographic comparing the orbit of the planet around Proxima Centauri (Proxima b) with the same region of the Solar System. Credit: ESO/M. Kornmesser/G. Coleman

Two separate papers discuss the habitability of Proxima b and its climate, both of which will be appearing soon on the Institute of Space Sciences (ICE) website. These papers describe the research team’s findings and outline their conclusions on how the existence of liquid water cannot be ruled out, and discuss where it is likely to be distributed.

Though there has been plenty of excitement thanks to words like “Earth-like”, “habitable zone”, and “liquid water” being thrown around, some clarifications need to be made. For instance, Proxima b’s rotation, the strong radiation it receives from its star, and its formation history mean that its climate is sure to be very different from Earth’s.

For instance, as is indicated in the two papers, Proxima b is not likely to have seasons, and water may only be present in the sunniest regions of the planet. Where those sunny regions are located depends entirely on the planet’s rotation. If, for example, it has a synchronous rotation with its star, water will only be present on the sun-facing side. If it has a 3:2 resoncance rotation, then water is likely to exist only in the planet’s tropical belt.

In any case, the discovery of this planet will open the door to further observations, using both existing instruments and the next-generation of space telescopes. And as Anglada-Escudé states, Proxima Centauri is also likely to become the focal point in the search for extra-terrestrial life in the coming years.

This picture combines a view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile with images of the stars Proxima Centauri (lower-right) and the double star Alpha Centauri AB (lower-left) from the NASA/ESA Hubble Space Telescope. Proxima Centauri is the closest star to the Solar System and is orbited by the planet Proxima b, which was discovered using the HARPS instrument on the ESO 3.6-metre telescope.
A view of the southern skies over the ESO 3.6-metre telescope at the La Silla Observatory in Chile, showing the location of Proxima Centauri in the sky. Credit: Y. Beletsky (LCO)/ESO/ESA/NASA/M. Zamani

“Many exoplanets have been found and many more will be found, but searching for the closest potential Earth-analogue and succeeding has been the experience of a lifetime for all of us,” he said. “Many people’s stories and efforts have converged on this discovery. The result is also a tribute to all of them. The search for life on Proxima b comes next…”

As we noted in a previous article on the subject, Project Starshot is currently developing a nanocraft that will use a laser-driven sail to make the journey to Alpha Centauri in 20 years time. But a mission to Proxima Centuari would take even less time (19.45 years at the same speed), and could study this newly-found exoplanet up-close.

One can only hope they are planning on altering their destination to take advantage of this discovery. And one can only imagine what they might find if and when they get to Proxima b!

A paper describing this milestone finding will be published in the journal Nature on August 25th, 2016, titled “A terrestrial planet candidate in a temperate orbit around Proxima Centauri“.

Further Reading: ESO

Discovered: Two New Planets for Kapteyn’s Star

The exoplanet discoveries have been coming fast and furious this week, as astronomers announced a new set of curious worlds this past Monday at the ongoing American Astronomical Society’s 224th Meeting being held in Boston, Massachusetts.

Now, chalk up two more worlds for a famous red dwarf star in our own galactic neck of the woods. An international team of astronomers including five researchers from the Carnegie Institution announced the discovery this week of two exoplanets orbiting Kapteyn’s Star, about 13 light years distant. The discovery was made utilizing data from the HIRES spectrometer at the Keck Observatory in Hawaii, as well as the Planet Finding Spectrometer at the Magellan/Las Campanas Observatory and the European Southern Observatory’s La Silla facility, both located in Chile.

The Carnegie Institution astronomers involved in the discovery were Pamela Arriagada, Ian Thompson, Jeff Crane, Steve Shectman, and Paul Butler. The planets were discerned using radial velocity measurements, a planet-hunting technique which looks for tiny periodic changes in the motion of a star caused by the gravitational tugging of an unseen companion.

“That we can make such precise measurements of such subtle effects is a real technological marvel,” said Jeff Crane of the Carnegie Observatories.

Kapteyn’s Star (pronounced Kapt-I-ne’s Star) was discovered by Dutch astronomer Jacobus Kapteyn during a photographic survey of the southern hemisphere sky in 1898. At the time, it had the highest proper motion of any star known at over 8” arc seconds a year — Kapteyn’s Star moves the diameter of a Full Moon across the sky every 225 years — and held this distinction until the discovery of Barnard’s Star in 1916. About a third the mass of our Sun, Kapteyn’s Star is an M-type red dwarf and is the closest halo star to our own solar system. Such stars are thought to be remnants of an ancient elliptical galaxy that was shredded and subsequently absorbed by our own Milky Way galaxy early on in its history. Its high relative velocity and retrograde orbit identify Kapteyn’s Star as a member of a remnant moving group of stars, the core of which may have been the glorious Omega Centauri star cluster.

The worlds of Kapteyn’s Star are proving to be curious in their own right as well.

“We were surprised to find planets orbiting Kapteyn’s Star,” said lead author Dr. Guillem Anglada-Escude, a former Carnegie post-doc now with the Queen Mary University at London. “Previous data showed some irregular motion, so we were looking for very short period planets when the new signals showed up loud and clear.”

The location of Kapteyn's Star in teh constellation Pictor. Created using Stellarium.
The location of Kapteyn’s Star in the constellation Pictor. Created using Stellarium.

It’s curious that nearby stars such as Kapteyn’s, Teegarden’s and Barnard’s star, though the site of many early controversial claims of exoplanets pre-1990’s, have never joined the ranks of known worlds which currently sits at 1,794 and counting until the discoveries of Kapteyn B and C. Kapteyn’s star is the 25th closest to our own and is located in the southern constellation Pictor. And if the name sounds familiar, that’s because it made our recent list of red dwarf stars for backyard telescopes. Shining at magnitude +8.9, Kapteyn’s star is visible from latitude 40 degrees north southward.

Kapteyn B and C are both suspected to be rocky super-Earths, at a minimum mass of 4.5 and 7 times that of Earth respectively. Kapteyn B orbits its primary once every 48.6 days at 0.168 A.U.s distant (about 40% of Mercury’s distance from our Sun) and Kapteyn C orbits once every 122 days at 0.3 A.U.s distant.

This is really intriguing, as Kapteyn B sits in the habitable zone of its host star. Though cooler than our Sun, the habitable zone of a red dwarf sits much closer in than what we enjoy in our own solar system. And although such worlds may have to contend with world-sterilizing flares, recent studies suggest that atmospheric convection coupled with tidal locking may allow for liquid water to exist on such worlds inside the “snow line”.

And add to this the fact that Kapteyn’s Star is estimated to be 11.5 billion years old, compared with the age of the universe at 13.7 billion years and our own Sun at 4.6 billion years. Miserly red dwarfs measure their future life spans in the trillions of years, far older than the present age of the universe.

A comparison of habitable zones of Sol-like versus Red dwarf stars. Credit: Chewie/Ignacio Javier under a Wikimedia Commons 3.0 license).
A comparison of habitable zones of Sol-like versus red dwarf stars. Credit: Chewie/Ignacio Javier under a Wikimedia Commons 3.0 license).

“Finding a stable planetary system with a potentially habitable planet orbiting one of the very nearest stars in the sky is mind blowing,” said second author and Carnegie postdoctoral researcher Pamela Arriagada. “This is one more piece of evidence that nearly all stars have planets, and that potentially habitable planets in our galaxy are as common as grains of sand on the beach.”

Of course, radial velocity measurements only give you lower mass constraints, as we don’t know the inclination of the orbits of the planets with respect to our line of sight. Still, this exciting discovery could potentially rank as the oldest habitable super-Earth yet discovered, and would make a great follow-up target for the direct imaging efforts or the TESS space telescope set to launch in 2017.

“It does make you wonder what kind of life could have evolved on those planets over such a long time,” added Dr Anglada-Escude. And certainly, the worlds of Kapteyn’s Star have had a much longer span of time for evolution to have taken hold than Earth… an exciting prospect, indeed!

-Read author Alastair Reynolds’ short science fiction piece Sad Kapteyn accompanying this week’s announcement.