Earthlike Exoplanets Are All Around Us

Artist’s impression of a rocky planet orbiting a red dwarf. Credit: David A. Aguilar (CfA)

We may literally be surrounded by potentially habitable exoplanets, according to new research by a team from the Harvard-Smithsonian Center for Astrophysics.

Using data gathered by NASA’s exoplanet-hunting Kepler spacecraft, the CfA researchers discovered that many red dwarf stars harbor planets, and some of those planets are rocky, Earth-sized worlds. Considering that red dwarfs, albeit optically dim, are the most abundant type of stars in our galaxy, this means that even a small percentage of them being host to Earthlike exoplanets puts the total number of potentially habitable worlds very high — and some of them could be right next door.

“We thought we would have to search vast distances to find an Earth-like planet,” said CfA astronomer and the paper’s lead author Courtney Dressing. “Now we realize another Earth is probably in our own backyard, waiting to be spotted.”

And our own backyard, in cosmic terms, could mean a mere 13 light-years away.

Our solar system is surrounded by red dwarfs. You can’t see them in the night sky because they are much too dim — less than a thousandth the brightness of the Sun. But they make up 75% of the stars in the local neighborhood, and based on the Kepler data the CfA team estimates that 6% of those red dwarfs likely have an Earth-sized planet in orbit around them.

And with at least 75 billion red dwarfs scattered across the galaxy… well, you do the math.*

“We now know the rate of occurrence of habitable planets around the most common stars in our galaxy,” said co-author David Charbonneau (CfA). “That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought.”


A visualization of the “unseen” red dwarfs in the night sky. Credit: D. Aguilar & C. Pulliam (CfA) See original here.

The conditions on a planet orbiting a red dwarf wouldn’t be exactly like Earth, of course. The planet would have to orbit rather closely to its star to be within its habitable zone, and would have to have a reasonably thick atmosphere to regulate heat and protect it from stellar outbursts. But one benefit to orbiting a red dwarf is that they have very long life spans — potentially longer than the current age of the Universe! So a habitable world around a red dwarf would literally have billions of years for life to evolve, thrive and develop on it.

“We might find an Earth that’s 10 billion years old,” Charbonneau said.

The team’s findings were presented today, Feb. 6, by Dressing during a press conference at the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. The results will be published in The Astrophysical Journal. (Added 2/7/13: here’s the video of the press conference.)

press_conference_d+c2013.pptxCfA astronomers identified 95 planetary candidates circling red dwarf stars. Of those, three orbit within the habitable zone (marked in green) – the distance at which they should be warm enough to host liquid water on the surface. Those three planetary candidates (marked with blue dots) are 0.9, 1.4, and 1.7 times the size of Earth. Credit: C. Dressing (CfA)

Read more on the CfA news release here.

*Ok, I did the math. That’s 4,500,000,000 Earth-like exoplanets around red dwarfs alone!

A Moon With Two Suns: Making Art from Science

A view of Kepler 47c and binary stars. ©Digital Drew. All rights reserved.

What would it look like on a hypothetical icy moon orbiting the exoplanet Kepler 47c? Perhaps something like this.

This is an illustration by an artist who goes by the name Digital Drew on Flickr. Drew creates landscapes of imagined alien worlds orbiting stars (and sometimes planets) that actually exist in the Universe. With 3D software, a little science and a lot of imagination, Drew shows us what skies might look like on other planets.

Kepler 47c (KOI-3154.02) is a Neptune-sized exoplanet orbiting a binary star pair 4,600 light-years away. It is part of the first circumbinary system ever discovered — one of at least two planets orbiting a pair of stars. In the image here, Kepler 47c is seen at upper left.

681737main_K47system_diagram_4x3_946-710What makes this exoplanet so exciting is that it is within the habitable zone around the stellar pair. So even though the planet itself may be a gas giant and thus not particularly suitable for life, any moons it has in orbit just might be.

While its slightly smaller planetary companion Kepler 47b orbits much too closely to the twin suns for water to exist as a liquid, 47c’s orbit is much farther out, completing one revolution every 303 days. Mainly illuminated by a star like our Sun but about 15% dimmer, this is a region where you could very well find a large rocky moon with conditions similar to Earth’s.

Fly a spacecraft over its higher elevations and you just might see a scene like this, a double sunset over a glacier-filled valley with a crescent gas giant dominating the sky. (Makes one wonder what the balmier regions might look like!)

“Unlike our sun, many stars are part of multiple-star systems where two or more stars orbit one another. The question always has been — do they have planets and planetary systems? This Kepler discovery proves that they do. In our search for habitable planets, we have found more opportunities for life to exist.”

– William Borucki, Kepler mission principal investigator (Sept. 2012)

And as more giant planets are discovered within their system’s habitable zones, the more there’s a chance that habitable moons could exist — or perhaps even be more common than habitable planets! Just recently the citizen science project Planet Hunters announced the potential exoplanet PH2 b, a Jupiter-sized world that orbits within a habitable zone. In our Solar System Jupiter has lots of moons; PH2 b could very well have a large number of moons of its own, any number of them with liquid water on their surfaces and temperatures “just right” for life.

Read more: Exciting Potential for Habitable Exomoons

While it will likely be quite some time before we see any direct observations of an actual exomoon, and possibly never from one, we must rely on the work of artists like Digital Drew to illustrate the many possibilities that exist.

See more of Drew’s work on his Flickr page here, and read more about the discovery of the Kepler 47 system here.

Inset image: Diagram of the Kepler 47 system compared to the inner Solar System. Credit: NASA/JPL-Caltech/T. Pyle.

Exciting Potential for Habitable ExoMoons

Imagine moons like Europa or Enceladus that are orbiting distant gas giant exoplanets located in the habitable zone of their star. What would be the potential for life on those moons? Hopefully one day we’ll find out, as that could be the scenario at an exoplanet that has been found by the Planet Hunter citizen science project. This is the second confirmed planet found by Planet Hunters, and the newest planet, PH2 b, is a Jupiter-size world in the habitable zone of a Sun-like star.

“There’s an obsession with finding Earth-like planets but what we are discovering, with planets such as PH2 b, is far stranger,” said Chris Lintott of Oxford University and Zooniverse. “Jupiter has several large water-rich moons – imagine dragging that system into the comfortably warm region where the Earth is. If such a planet had Earth size moons, we”d see not Europa and Callisto but worlds with rivers,lakes and all sorts of habitats – a surprising scenario that might just be common.”

Astronomers with Planet Hunters estimate the surface temperature PH2 b is 46 degrees Celsius. That’s a “just right” temperature for there to be liquid water, but it is extremely unlikely that life exists on PH2 b because it is a gas planet, and might be similar to Jupiter, so there is no solid surface or liquid environment for life to thrive. But if this planet is anything like the gas giant planets in our solar sytem, there could be a plethora of moons orbiting them.

“We can speculate that PH2 b might have a rocky moon that would be suitable for life, said lead author of the paper that has been published in arXiv, Dr Ji Wang, from Yale University. I can’t wait for the day when astronomers report detecting signs of life on other worlds instead of just locating potentially habitable environments. That could happen any day now.”

Additionally, the Zooniverse’s Planet Hunters team announced today that their citizen science volunteers have discovered 31 long-period planet candidates, with 15 of these new planet candidates orbiting in the habitable zones of other stars.

The team said that with 19 similar planets already discovered in habitable zones, where the temperature is neither too hot nor too cold for liquid water, the new finds suggest that there may be a “traffic jam” of all kinds of strange worlds in regions that could potentially support life.

Although most of these planets are large, like Neptune or Jupiter, these discoveries increase the sample size of long-period planet candidates by more than 30% and almost double the number of known gas giant planet candidates in the habitable zone, Wang said. “In the future, we may find moons around these planet candidates (just like Pandora around Polyphemus in the movie Avatar) that allows life to survive and evolve under a habitable temperature.”

They also have a “watch list” for 9 further planet candidates which have only 2 transits observed.

To study the PH2 b system, the astronomy team from Planet Hunters used the HIRES spectrograph and NIRC2 adaptive optics system on the Keck telescopes in Hawaii to obtain both high resolution spectrum and high spatial-resolution images.

“The observations help us to rule out possible scenarios for false positive detections and give us a measured confidence level of more than 99.9% that PH2 b is a bona-fide planet rather than just an illusion,” Wang wrote on the Planet Hunter’s blog.

More than 40 volunteers were listed as co-authors on the paper, acknowledging the contributions of hundreds of volunteers to the effort. Among them is Roy Jackson, a 71-year-old retired police officer who lives in Birtley, near Gateshead. He said:
“It is difficult to put into words, the pleasure, wonderment and perhaps even pride that I have in some small way been able to assist in the discovery of a planet. But I would like to say that the discovery makes the time spent on the search well worth the effort.”

Mark Hadley, an electronics engineer from Faversham, another of the Planet Hunters credited on the paper, said: “Now, when people ask me what I achieved last year I can say I have helped discover a possible new planet around a distant star! How cool is that?”

“These are planet candidates that slipped through the net, being missed by professional astronomers and rescued by volunteers in front of their web browsers,” said Lintott. It’s remarkable to think that absolutely anyone can discover a planet.”

Sources: Yale University, Planet Hunters blog.

Kepler Finds Hundreds of New Exoplanet Candidates

Artist’s depiction of the Kepler 10 system, which contains planets 2.2 and 1.4 times the size of Earth. (NASA/Ames/JPL-Caltech)

Kepler mission scientists announced today the discovery of literally hundreds of new exoplanet candidates — 461, to be exact — orbiting distant stars within a relatively small cross-section of our galaxy, bringing the total number of potential planets awaiting confirmation to 2,740. What’s more, at least 4 of these new candidates appear to be fairly Earth-sized worlds located within their stars’ habitable zone, the orbital “sweet spot” where surface water could exist as a liquid.

Impressive results, considering that NASA’s planet-hunting spacecraft was launched a little under 4 years ago (and watching 150,000 stars to spot the shadows of planets is no easy task!)

“… the ways by which men arrive at knowledge of the celestial things are hardly less wonderful than the nature of these things themselves.”

— Johannes Kepler

Since the last official announcement of Kepler candidates in Feb. 2012 the number of smaller Earth- and super-Earth-sized worlds observed has risen considerably, as well as the identification of multi-planet systems that are organized more-or-less along a flat plane… just like ours.

“There is no better way to kickoff the start of the Kepler extended mission,” said Kepler scientist Christopher Burke, “than to discover more possible outposts on the frontier of potentially life bearing worlds.”

Read more: First Earth-Sized Exoplanets Found by Kepler

From the NASA press release:

Since the last Kepler catalog was released in February 2012, the number of candidates discovered in the Kepler data has increased by 20 percent and now totals 2,740 potential planets orbiting 2,036 stars. The most dramatic increases are seen in the number of Earth-size and super Earth-size candidates discovered, which grew by 43 and 21 percent respectively.

The new data increases the number of stars discovered to have more than one planet candidate from 365 to 467. Today, 43 percent of Kepler’s planet candidates are observed to have neighbor planets.


The most dramatic increases are seen in the number of Earth-size and super Earth-size candidates discovered, which grew by 43 and 21 percent respectively. (NASA)

Although some of the new candidates announced today are large Neptune-sized planets, more than half are Earth- to super-Earth sized worlds less than twice the radius of our own planet.

KeplerfieldofviewwithMilkyWayIn order for Kepler candidates to be “officially” called exoplanets, they must be observed 3 times on a regular orbit — that is, their signature dimming of the light from their home star must occur as predicted once their presence and then orbital period is calculated. Only then is an exoplanet confirmed.

To date Kepler has confirmed 105 exoplanets.

The longer the mission continues, the better the chance that Kepler will be able to confirm smaller Earth-sized worlds in longer-period orbits.

Read more: Kepler Mission Extended to 2016

“The analysis of increasingly longer time periods of Kepler data uncovers smaller planets in longer period orbits — orbital periods similar to Earth’s,” said Steve Howell, Kepler mission scientist. “It is no longer a question of will we find a true Earth analogue, but a question of when.”

Scientists analyzed more than 13,000 transit-like signals called ‘threshold crossing events’ to eliminate known spacecraft instrumentation and astrophysical false positives, phenomena that masquerade as planetary candidates, to identify the potential new planets. Watch the video below to see how Kepler observes the light-curve of transit events.

Read more on the NASA press release, and learn more about the Kepler mission here.

Nearly All Sun-Like Stars Have Planetary Systems

The latest analysis of data from the Kepler planet-hunting spacecraft reveals that almost all stars have planets, and about 17 percent of stars have an Earth-sized planet in an orbit closer than Mercury. Since the Milky Way has about 100 billion stars, there are at least 17 billion Earth-sized worlds out there, according to Francois Fressin of the Harvard-Smithsonian Center for Astrophysics (CfA), who presented new findings today in a press conference at the American Astronomical Society meeting in Long Beach, California. Moreover, he said, almost all Sun-like stars have planetary systems.

The holy grail of planet-hunting is finding a twin of Earth – a planet of about the same size and in the habitable zone around similar star. The odds of finding such a planet is becoming more likely Fressin said, as the latest analysis shows that small planets are equally common around small and large stars.

While the list of Kepler planetary candidates contains majority of the knowledge we have about exoplanets, Fressin said the catalog is not yet complete, and the catalog is not pure. “There are false positives from events such as eclipsing binaries and other astrophysical configurations that can mimic planet signals,” Fressin said.

By doing a simulation of the Kepler survey and focusing on the false positives, they can only account for 9.5% of the huge number of Kepler candidates. The rest are bona-fide planets.

This artist's illustration represents the variety of planets being detected by NASA's Kepler spacecraft. Credit: C. Pulliam & D. Aguilar (CfA)
This artist's illustration represents the variety of planets being detected by NASA's Kepler spacecraft. Credit: C. Pulliam & D. Aguilar (CfA)

Altogether, the researchers found that 50 percent of stars have a planet of Earth-size or larger in a close orbit. By adding larger planets, which have been detected in wider orbits up to the orbital distance of the Earth, this number reaches 70 percent.

Extrapolating from Kepler’s currently ongoing observations and results from other detection techniques, it looks like practically all Sun-like stars have planets.

The team then grouped planets into five different sizes. They found that 17 percent of stars have a planet 0.8 – 1.25 times the size of Earth in an orbit of 85 days or less. About one-fourth of stars have a super-Earth (1.25 – 2 times the size of Earth) in an orbit of 150 days or less. (Larger planets can be detected at greater distances more easily.) The same fraction of stars has a mini-Neptune (2 – 4 times Earth) in orbits up to 250 days long.

Larger planets are much less common. Only about 3 percent of stars have a large Neptune (4 – 6 times Earth), and only 5 percent of stars have a gas giant (6 – 22 times Earth) in an orbit of 400 days or less.

The researchers also asked whether certain sizes of planets are more or less common around certain types of stars. They found that for every planet size except gas giants, the type of star doesn’t matter. Neptunes are found just as frequently around red dwarfs as they are around sun-like stars. The same is true for smaller worlds. This contradicts previous findings.

“Earths and super-Earths aren’t picky. We’re finding them in all kinds of neighborhoods,” says co-author Guillermo Torres of the CfA.

Planets closer to their stars are easier to find because they transit more frequently. As more data are gathered, planets in larger orbits will come to light. In particular, Kepler’s extended mission should allow it to spot Earth-sized planets at greater distances, including Earth-like orbits in the habitable zone.

Kepler detects planetary candidates using the transit method, watching for a planet to cross its star and create a mini-eclipse that dims the star slightly.

Sources: Harvard Smithsonian CfA, AAS Press Conference

Here There Be Planets: Stellar Disk Gap May Reveal Newborn Worlds

HiCIAO near-infrared image of the protoplanetary disk around PDS 70. The circular mask hides the star itself, as well as a smaller internal disk structure. (Credit: NAOJ)

Over the past couple of decades astronomers have figured out several methods for finding planets around other stars in our galaxy. Some have revealed their presence by the slight “wobble” they impart to their host stars as they orbit, while others have been discovered as they pass in front of their stars from our perspective, briefly dimming the light we see.

Now, some astronomers think they may have identified the presence of multiple planets, based on a large gap found in the disk of  gas and dust surrounding a Sun-like star 460 light-years from Earth.

Using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) mounted on Japan’s 8.2-meter optical-infrared Subaru telescope atop Mauna Kea in Hawaii, an international team of astronomers targeted PDS 70, a young star (10 million years old) about the same mass as the Sun located 460 light-years away in the constellation Centaurus.

The near-infrared observations made by HiCIAO reveal a protoplanetary disk surrounding PDS 70. This disk is composed of gas and dust and extends billions of miles out from the star. Quite literally the stuff that planets are made of, it’s a disk much like this that our solar system likely started out as over 4.6 billion years ago.

“Thanks to the powerful combination of the Subaru Telescope and HiCIAO, we are able to probe the disks around Sun-like stars. PDS 70 shows how our solar system may have looked in its infancy. I want to continue this kind of research to understand the history of planetary formation.”

– Team Leader Jun Hashimoto (NAOJ)

Within PDS 70’s disk are several large gaps positioned at varying distances from the star itself, appearing as dark regions in the near-infrared data. These gaps — especially the largest, located about 70 AU from the star — are thought to be the result of newly-formed planets having cleared the surrounding space of dust and smaller material. It’s also believed that multiple planets may be present since, according to the team, “no single planet, regardless of how heavy or efficient it is in its formation, is sufficient to create such a giant gap.”

In addition to the large disk structure and outer gap, PDS 70 also has a smaller disk located only 1 AU away. (This disk is obscured by the HiCIAO mask in the image above.)

Further observations will be needed to locate any actual exoplanets directly, since the light from the star and scattered light within the disk makes it difficult — if not impossible with current technology — to detect the incredibly faint light reflected by planets.

Still, it’s fascinating to come across what may very well be a solar system in its infancy, giving us a glimpse back in time to our own formation.

“Direct imaging of planets in the process of forming in protoplanetary disks would be ideal so that we can learn when, where, and how planets form,” said team leader Ruobing Dong of Princeton University.

Read more on the NAOJ website for the Subaru Observatory here.

The goal of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) Project is to study the disks around less massive stars like the Sun.

Inset image: Artist’s rendition of PDS 70 and its two protoplanetary disks (NAOJ)

Want to Name an Exoplanet? Uwingu Has a Plan

Screenshot from the Uwingu exoplanet naming website.

Astronomers have now discovered nearly 1,000 planets orbiting other stars, and right now these exoplanets all have boring, license-plate-like names, such as HD85512 and GJ 436 instead of endearing, “real” planet names that might offer hints of what that world could be like. And recall the recent extrapolation of how many habitable planets might be in the Milky Way? A team using the ESO’s HARP’s spectrograph determined there might be upwards of 160 billion worlds out there for us to find, and perhaps eventually name. How might we come up with that many names?

Uwingu, a startup company that is hoping to use innovative ways to fund space and astronomy research, has an idea of how to do that. Their first commercial project is to challenge people to create a ‘baby book of planet names’ for all these planets, as suggestions for future names for other worlds.

“The many, many planets discovered across the galaxy in past 20 years are a tribute to our natural human desire to explore beyond the horizon,” said noted planet hunter Dr. Geoff Marcy of the University of California at Berkeley, who is also an advisor for Uwingu. “Now people all over the world can participate in these discoveries in a new way, giving identities and even personality to billions of planets in our galaxy for the first time.”

How does this raise money for space science? Submitting suggestions for names cost $.99 each, and Uwingu will use proceeds from this project and future ones to create funds for grants that space researchers, space educators, and project teams can apply to use.

Uwingu’s first project is technically now in “beta testing,” and in a press release, the organization said the public can participate immediately, helping to generate a new source of funds for space exploration, research, and education.

But it doesn’t end with just suggestions. People can vote on the top names (each vote also costs $.99), and as Uwingu CEO and founder Alan Stern told Universe Today, they are hoping the voting goes viral among the social media savvy.

“This is a way for people everywhere to connect with space,” he said. “You can suggest a name and tell all your friends to vote, and the top names will be the first to be used. If you nominate the name of someone famous, hopefully they’ll get in on the excitement and ask their fans to vote, too.”

The Uwingu team suggests nominating planet names for your favorite town, state, or country, your favorite sports team, music artist, or hero, your favorite author or book, your school, your company, for your loved ones and friends, or even for yourself.

The names won’t be officially approved by the International Astronomical Union, but Stern said they will be are similar to the names given to features on Mars by the mission science teams (such as the “Jake Matijevic” rock recently analyzed by the Curiosity rover) that everyone ends up using. This also solves the problem of how to come up with names, a task that the IAU has yet to discuss.

Initial reactions to the planet naming project – and to Uwingu itself — have been mixed. During their Indigogo fundraising, the Uwingu team didn’t disclose what types of things they would be selling or doing to raise funds, which was a concern to some in the space and astronomy community who normally support almost any space-related initiative. In a previous interview with UT, Stern said being secretive was a way to generate interest and likened it to how Apple announces a new product.

While there seems to be excitement about the opportunity to suggest names for exoplanets (as of this writing 74 names had been nominated, with numerous votes for each name), some early reactions have been that this might be similar to the ‘name a star’ registries that are unofficial and quite expensive.

IAU’s stance on naming exoplanets has been that since it appears there are going to be so many of them, naming them will be difficult. However, in an email reply, the former president of the IAU Planetary Systems Science body, Karen Meech said that at the IAU meeting in Beijing this summer there was discussion about the need to set up a group to look into the issue of exoplanet names.

And Meech did confirm that since the IAU is the only scientifically recognized arbiter of astronomical names, any contests for names from the public will not be officially recognized by the scientific community.

But if the problem is in the amount of names that will be required, that’s where Uwingu’s crowd sourcing idea seems to fit the need.

And for those who are critical of Uwingu’s methods, Uwingu is so far the only group or organization to step forward with innovative, out-of-the-box ways to try and solve what seems to be a continuous, perennial problem: how to fund creative space and astronomy projects and move beyond the old tried and not always true methods of relying on government grants and subsidies or angel donors.

Uwingu is at least trying something different, and it will be interesting to see how this plays out. Stern said earlier that Uwingu’s projects would appeal to the general public, not just the space and astronomy community, to provide a bigger marketplace for their projects. He indicated Uwingu will be coming out with another project in a few months.

We humans love to name things: we name our cars, spacecraft and rocks, craters and hills on other planets. NASA has had contests to name missions, rovers, and modules on the ISS, all of which has generated excitement among the public. Science and science fiction fans have expressed disappointment at the names given to exoplanets so far (they certainly aren’t as intriguing as names we’ve come to love like Tatooine, Pandora, Vulcan or Hoth.) Uwingu is using that innate need/love of naming things to try and move space science and astronomy into a new era.

Possible Subterranean Life Means More Exoplanets Could Harbor Life

Artistic representation of the current five known potential habitable worlds. Will this list broaden under a new habitability model? Credit: The Planetary Habitability Laboratory (PHL)

When we think of life on other planets, we tend to imagine things (microbes, plant life and yes, humanoids) that exist on the surface. But Earth’s biosphere doesn’t stop at the planet’s surface, and neither would life on another world, says a new study that expands the so-called ‘Goldilocks Zone’ to include the possibility of subterranean habitable zones. This new model of habitability could vastly increase where we could expect to find life, as well as potentially increasing the number of habitable exoplanets.

We know that a large fraction of the Earth’s biomass is dwelling down below, and recently microbiologists discovered bacterial life, 1.4 kilometers below the sea floor in the North Atlantic, deeper in the Earth’s crust than ever before. This and other drilling projects have brought up evidence of hearty microbes thriving in deep rock sediments. Some derive energy from chemical reactions in rocks and others feed on organic seepage from life on the surface. But most life requires at least some form of water.

“Life ‘as we know it’ requires liquid water,” said Sean McMahon, a PhD student from the University of Aberdeen’s (Scotland) School of Geosciences. “Traditionally, planets have been considered ‘habitable’ if they are in the ‘Goldilocks zone’. They need to be not too close to their sun but also not too far away for liquid water to persist, rather than boiling or freezing, on the surface. However, we now know that many micro-organisms—perhaps half of all living things on Earth—reside deep in the rocky crust of the planet, not on the surface.”

Location in the night sky of the stars with potential habitable exoplanets (red circles). There are two in Gliese 581. Click the image for larger version. CREDIT: PHL @ UPR Arecibo and Jim Cornmell.

While suns warm planet surfaces, there’ also heat from the planets’ interiors. Crust temperature increases with depth so planets that are too cold for liquid water on the surface may be sufficiently warm underground to support life.

“We have developed a new model to show how ‘Goldilocks zones’ can be calculated for underground water and hence life,” McMahon said. “Our model shows that habitable planets could be much more widespread than previously thought.”

In the past, the Goldilocks zone has really been determined by a circumstellar habitable zone (CHZ), which is a range of distances from a star, and depending on the star’s characteristics, the zone varies. The consensus has been that planets that form from Earth-like materials within a star’s CHZ are able to maintain liquid water on their surfaces.
But McMahon and his professor, John Parnell, also from Aberdeen University who is leading the study now are introducing a new term: subsurface-habitability zone (SSHZ). This denote the range of distances from a star within which planets are habitable at any depth below their surfaces up to a certain maximum, for example, they mentioned a “SSHZ for 2 km depth”, within which planets can support liquid water 2 km or less underground.

If this notion catches on – which it should – it will have exoplanet hunters recalculating the amount of potentially habitable worlds.

The research was presented at the annual British Science Festival in Aberdeen.

Source: University of Aberdeen

See also: The Habitable Exoplanets Catalogue from the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo.

What If All of Kepler’s Exoplanets Orbited the Same Star?

That’s exactly the scenario shown by a mesmerizing animation called “Worlds” by Alex Parker — a single system containing 2299 multiple-transit planetary candidates identified to date by NASA’s Kepler space telescope, which is currently scrutinizing a field of view within the constellation Cygnus to detect the oh-so-faint reductions in brightness caused by planets passing in front of their stars.

The search requires patience and precision; it’s not really this crowded out there.

Alex’s animation takes 2299 candidates that have been observed multiple times, each shown to scale in relation to their home star, and puts them in orbit around one star, at their relative distances.

The result, although extravagantly impossible, is no less fascinating to watch. (I suggest going full screen.)

“The Kepler observatory has detected a multitude of planet candidates orbiting distant stars,” Alex writes on his Vimeo page. “The current list contains 2321 planet candidates, though some of these have already been flagged as likely false-positives or contamination from binary stars. This animation does not contain circumbinary planets or planet candidates where only a single transit has been observed, which is why ‘only’ 2299 are shown.

“A fraction of these candidates will likely be ruled out as false positives as time goes on, while the remainder stand to be confirmed as real planets by follow-up analysis,” Alex adds.

The white ellipses seen when the animation pulls back are the relative sizes of the orbits of Mercury, Venus and Earth.

At this time the Kepler mission has identified 2321 planetary candidates, with 74 exoplanets confirmed. See more on the Kepler mission here.

Animation: Alex Parker. Image: Kepler mission planet candidates family portrait (NASA Ames/Jason Rowe/Wendy Stenzel)

Two “b”‘s in the Beehive

Praesepe (aka. the Beehive Cluster)

As astronomers near the 800 mark for confirmed extra solar planets, it seems that notable milestones are becoming fewer and further between. Multi-planet systems aren’t even worth mentioning. Planets less massive than Earth? Already heard about it. Detecting atmospheres? Old news.

But a recent paper manages to sneak in one new first: The first detection of hot Jupiters in an open cluster. This discovery is not simply notable due to the novelty, but clusters have special characteristics that can help astronomers determine more of the history of the system.

The discovery was made by astronomers at Georgia State University using the “wobble” method in which they looked for the spectroscopic wiggle of spectral lines as planets tugged their parent stars around in orbit. The Beehive Cluster was chosen because it is a nearby cluster with over 1,000 member stars, many of which are similar in mass to the Sun. Additionally, the cluster is known to have an above average metallicity which is known to be correlated with planetary systems.

Searches of other open clusters have largely come up empty. Only two stars in open clusters have so far been found to have planets and both of those are around giant stars and as such, the planets are in wide orbits. This paucity is odd since stars are expected to form in clusters, and as such, the frequency of planets in clusters should be nearly the same as isolated stars.

The team used the 1.5-m Tillinghast Reflector at the Fred L. Whipple Observatory on Mt. Hopkins, Arizona observing a total of 53 stars in the cluster. Their results uncovered two new hot Jupiter planets in tight orbits around the parent, main-sequence stars. The first has an estimated mass of 0.54 times that of Jupiter while the second weighs in at 1.8 Jupiter masses.

The discovery helps to place constraints on how planets form and migrate in fledgling systems. Since massive planets such as these would need to form further out in colder parts of the circumstellar cloud, such planets would have to move inwards. The time period in which this happens has been a difficult question for astronomers to pin down. But since the Beehive cluster is only 600 million years old and these new planets are already in tight orbits, this helps to demonstrate that such migration is possible on short timescales.

While these are the first of their kind discovered in open clusters, this discovery puts the number of hot Jupiters in open clusters in rough agreement with expectations based on the number of such systems of stars that are no longer bound in clusters. This finding bridges the gap between formation and isolated stars that previous searches of open clusters had left open.