Jupiter and its four planet-size moons, called the Galilean satellites photographed and assembled into a collage by NASA.
Last year, physicists worked out the plausibility of a fully functional (if not fictional) Death Star being able to destroy planets, and found that the Galactic Empire’s technological terror could indeed destroy Earth-like rocky planets, but a Jupiter-sized gas planet would be a tough challenge.
Now, real but theoretical modeling confirms that gas giants like Jupiter would be really hard to destroy by any means, including by stars that undergo periodic outbursts. Actual stars, that is, not Death Stars.
Alan Boss is a noted astrophysicist at the Carnegie Institution of Washington, Department of Terrestrial Magnetism, who likes to create three dimensional models of planetary systems. In his recent work, he created 3-D models to help understand the possible origins of Jupiter and Saturn, two gas giants in our Solar System.
He created different models of new stars, which are surrounded by rotating gas disks where planets are thought to form. His models were based on different theories of planetary formation, such as that planets could form from slowly growing ice and rock cores, followed by rapid accretion of gas from the surrounding disk, or that planets form from clumps of dense gas, which increase in mass and density, forming a gas giant planet in a single step.
What he found was, that regardless of how gas giant planets form, they should be able to survive periodic outbursts of mass transfer from the gas disk onto the young star. One model similar to our own Solar System was stable for more than 1,000 years, while another model containing planets similar to our Jupiter and Saturn was stable for more than 3,800 years. The models showed that these planets were able to avoid being forced to migrate inward to be swallowed by the growing proto-sun, or being tossed completely out of the planetary system by close encounters with each other.
“Gas giant planets, once formed, can be hard to destroy,” said Boss, “even during the energetic outbursts that young stars experience.”
Some Sun-like stars undergo these periodic outbursts which can last about 100 years. The Death Star, on the other hand — which according to Star Wars lore, is a moon-sized battle station designed to spread fear throughout the galaxy – uses short bursts of its hypermatter reactor superlaser. However, the Death Star’s main power reactor is said to have the energy output equal to several main-sequence stars. But to destroy a planet like Jupiter, all power from essential systems and life support would be required, which is not necessarily possible.
So, in all cases – real, theoretical and fictional — gas giants appear to be safe!
Boss is the author of The Crowded Universe, a book on the likelihood of finding life and habitable planets outside of our Solar System, and Looking For Earths, about the race to find new solar systems.
This image from the NACO system on ESO’s Very Large Telescope shows a candidate protoplanet in the disc of gas and dust around the young star HD100546. Credit: ESO.
Astronomers have taken what is likely the first-ever direct image of a planet that is still undergoing its formation, embedded in its “womb” of gas and dust. The protoplanet, about the size of Jupiter, is in the disc surrounding a young star, HD 100546, located 335 light-years from Earth.
If this discovery is confirmed, astronomers say this it will greatly improve our understanding of how planets form and allow astronomers to test the current theories against an observable target.
“So far, planet formation has mostly been a topic tackled by computer simulations,” said Sascha Quanz, from ETH Zurich in Switzerland, who led an international team using the Very Large Telescope to make the observations. “If our discovery is indeed a forming planet, then for the first time scientists will be able to study the planet formation process and the interaction of a forming planet and its natal environment empirically at a very early stage.”
The protoplanet appears as a faint blob in the circumstellar disc of HD 100546, a well-studied star, and astronomers have already discovered other protoplanets orbiting this star. In 2003, astronomers used a technique called “nulling interferometry” to reveal not only the planetary disk, but also discovered a gap in the disk, where a Jupiter-like planet is probably forming about six times farther form the star than Earth is from the Sun. This newly found planet candidate is located in the outer regions of the system, about ten times further out.
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The team used the VLT along with a near-infrared coronograph in an adaptive optics instrument called NACO, which enabled them to suppresses the bright light of the star, combined with pioneering data analysis techniques.
The current theory of planet formation is based mostly on observations of our own solar system. Since 1995, when the first exoplanet around a Sun-like star was discovered, several hundred planetary systems have been found, opening up new opportunities for scientists studying planetary formation. But until now, none have been “caught in the act” in the process of being formed, while still embedded in the disc of material around their young parent star.
This composite image shows a view from the NASA/ESA Hubble Space Telescope (left) and from the NACO system on ESO’s Very Large Telescope (right) of the gas and dust around the young star HD 100546. The Hubble visible-light image shows the outer disc of gas and dust around the star. The new infrared VLT picture of a small part of the disc shows a candidate protoplanet. Both pictures were taken with a special coronagraph that suppresses the light from the brilliant star. The position of the star is marked with a red cross in both panels. Credit: ESO/NASA/ESA/Ardila et al.
But in studying the disc around HD 100546, astronomers have spotted several features that support the current theory that giant planets grow by capturing some of the gas and dust that remains after the formation of a star. They have seen structures in the dusty circumstellar disc, which could be caused by interactions between the planet and the disc, as well as indications that the surroundings of the protoplanet are being heated up by the formation process.
The astronomers are doing follow-up observations to confirm the discovery, as it is possible that the detected signal could have come from an unrelated background source, or it could possibly be a fully formed planet which was ejected from its original orbit closer to the star. But the researchers say the most likely explanation is that this is actually the first protplanet that has been directly imaged.
A ghostly blue ring is a planetary nebula - hydrogen gas the star ejected as it evolved from a red giant to a white dwarf.
Credit: David A. Aguilar (CfA)
We’ve currently found 867 different exoplanets, but have yet to definitely determine if one of those harbors life. How will astronomers make that determination? They’ll look at things such as its composition, orbital properties, atmosphere, and potential chemical interactions. While oxygen is relatively abundant in the Universe, finding it in the atmosphere of a distant planet could point to its habitability because its presence – in large quantities — would signal the likely presence of life.
But where to look first? A new study finds that we could detect oxygen in the atmosphere of a habitable planet orbiting a white dwarf – a star that is in the process of dying — much more easily than for an Earth-like planet orbiting a Sun-like star.
“In the quest for extraterrestrial biological signatures, the first stars we study should be white dwarfs,” said Avi Loeb, theorist at the Harvard-Smithsonian Center for Astrophysics (CfA) and director of the Institute for Theory and Computation.
Loeb and his colleague Dan Maoz from Tel Aviv University estimate that a survey of the 500 closest white dwarfs could spot one or more habitable Earths.
Potential habitable exoplanets, as of Feb. 18, 2013. Credit: The Planetary Habitability Labratory at UPR/Arecibo.
A white dwarf is what stars like the Sun become after they have exhausted their nuclear fuel. It puffs off its outer layers, leaving behind a hot core which can be about the size of Earth. It slowly cools and fades over time, but it can retain heat long enough to warm a nearby world for billions of years.
Currently, most planets that we’ve found orbit close to their parent star, since astronomers find planets using astrometry by the gravitational influence the planet has on the star, causing it to wobble ever so slightly. Massive planets close to the star have the biggest effect and so are the easiest to detect.
Using the photometry, astronomers see a dip in the amount of light a star gives off when a planet passes in front of the star. Since a white dwarf is about the same size as Earth, an Earth-sized planet would block a large fraction of its light and create an obvious signal. Photometry, or the transit method, has proven the best way to find exoplanets.
A white dwarf is much smaller and fainter than the Sun, and a planet would have to be much closer in to be habitable with liquid water on its surface, so that should make planets around a white dwarf star easier to detect. A habitable planet would circle the white dwarf once every 10 hours at a distance of about a million miles.
More importantly, we can only study the atmospheres of transiting planets. When the white dwarf’s light shines through the ring of air that surrounds the planet’s silhouetted disk, the atmosphere absorbs some starlight. This leaves chemical fingerprints showing whether that air contains water vapor, or even signatures of life, such as oxygen.
But there’s a caveat: Before a star becomes a white dwarf it swells into a red giant, engulfing and destroying any nearby planets. Therefore, a planet would have to arrive in the habitable zone after the star evolved into a white dwarf. Either it would migrate towards the star from a more distant orbit or be a new planet formed from leftover dust and gas.
However, we have yet to find a exoplanet around a white dwarf, even though Loeb and Moaz say the abundance of heavy elements on the surface of white dwarfs suggests that a significant fraction of them have rocky planets.
We need a better eye in the sky to find planets around white dwarfs, say Loeb and Maoz, and the James Webb Space Telescope (JWST), scheduled for launch by the end of this decade, promises to sniff out the gases of these alien worlds.
Loeb and Maoz created a synthetic spectrum, replicating what JWST would see if it examined a habitable planet orbiting a white dwarf. They found that both oxygen and water vapor would be detectable with only a few hours of total observation time.
“JWST offers the best hope of finding an inhabited planet in the near future,” said Maoz.
The James Webb Space Telescope. Credit: NASA
Recent research by CfA astronomers Courtney Dressing and David Charbonneau showed that the closest habitable planet is likely to orbit a red dwarf star (a cool, low-mass star undergoing nuclear fusion). Since a red dwarf, although smaller and fainter than the Sun, is much larger and brighter than a white dwarf, its glare would overwhelm the faint signal from an orbiting planet’s atmosphere. JWST would have to observe hundreds of hours of transits to have any hope of analyzing the atmosphere’s composition.
“Although the closest habitable planet might orbit a red dwarf star, the closest one we can easily prove to be life-bearing might orbit a white dwarf,” said Loeb.
NASA's Kepler mission has discovered a new planetary system that is home to the smallest planet yet found around a star like our sun, approximately 210 light-years away in the constellation Lyra. Credit: NASA/Ames/JPL-Caltech
Scientists have discovered a new planet orbiting a Sun-like star, and the exoplanet is the smallest yet found in data from the Kepler mission. The planet, Kepler-37b, is smaller than Mercury, but slightly larger than Earth’s Moon. The planet’s discovery came from a collaboration between Kepler scientists and a consortium of international researchers who employ asteroseismology — measuring oscillations in the star’s brightness caused by continuous star-quakes, and turning those tiny variations in the star’s light into sounds.
“That’s basically listening to the star by measuring sound waves,” said Steve Kawaler, from Iowa State University in the US, and a member of the research team. “The bigger the star, the lower the frequency, or ‘pitch’ of its song.”
The measurements made by the astroseismologists allowed the Kepler research team to more accurately measure the tiny Kepler-37b, as well as revealing two other planets in the same planetary system: one slightly smaller than Earth and one twice as large.
While Kepler 37b is likely a rocky planet, this would not be a great place for humans to live. It’s likely very hot — with a smoldering surface and no atmosphere.
“Owing to its extremely small size, similar to that of the Earth’s moon, and highly irradiated surface, Kepler-37b is very likely a rocky planet with no atmosphere or water, similar to Mercury,” the team wrote in their paper, which was published this week in Nature. “The detection of such a small planet shows for the first time that stellar systems host planets much smaller as well as much larger than anything we see in our own Solar System.”
The host star, Kepler-37, is about 210 light-years from Earth in the constellation Lyra. All three planets orbit the star at less than the distance Mercury is to the Sun, suggesting they are very hot, inhospitable worlds. Kepler-37b orbits every 13 days at less than one-third Mercury’s distance from the Sun. The estimated surface temperature of this smoldering planet, at more than 800 degrees Fahrenheit (700 Kelvin), would be hot enough to melt the zinc in a penny. Kepler-37c and Kepler-37d, orbit every 21 days and 40 days, respectively.
Artist’s concept of Kepler-37b. The planet is slightly larger than our moon, measuring about one-third the size of Earth. Credit: NASA/Ames/JPL-Caltech
The size of the star must be known in order to measure the planet’s size accurately. To learn more about the properties of the star Kepler-37, scientists examined sound waves generated by the boiling motion beneath the surface of the star.
“The technique for stellar seismology is analogous to how geologists use seismic waves generated by earthquakes to probe the interior structure of Earth,” said Travis Metcalfe, who is part of the Kepler Asteroseismic Science Consortium.
The sound waves travel into the star and bring information back up to the surface. The waves cause oscillations that Kepler observes as a rapid flickering of the star’s brightness. The barely discernible, high-frequency oscillations in the brightness of small stars are the most difficult to measure. This is why most objects previously subjected to asteroseismic analysis are larger than the Sun.
“Studying these oscillations been done for a long time with our own Sun,” Metcalfe told Universe Today, “but the Kepler mission expanded that to hundreds of Sun-like stars. Kepler-37 is the coolest star, as well as the smallest star that has been measured with asterosiesmology.”
Kepler-37 has a radius just three-quarters of the Sun. Metcalfe said the radius of the star is known to 3 percent accuracy, which translates to exceptional accuracy in the planet’s size.
Metcalfe launched a non-profit organization to help raise research funds for the Kepler Asteroseismic Science Consortium. The Pale Blue Dot Project allows people to adopt a star to support asteroseismology, since there is no NASA funding for asteroseismology.
“Much of the expertise for this exists in Europe and not in the US, so as a cost saving measure NASA outsourced this particular research for the Kepler mission,” said Metcalfe, “and NASA can’t fund researchers in other countries.”
The Kepler spacecraft carries a photometer, or light meter, to measure changes in the brightness of the stars it is focusing on in the Cygnus region in the sky.
Kepler Mission Star Field. An image by Carter Roberts of the Eastbay Astronomical Society in Oakland, CA, showing the Milky Way region of the sky where the Kepler spacecraft/photometer is pointing. Each rectangle indicates the specific region of the sky covered by each CCD element of the Kepler photometer. There are a total of 42 CCD elements in pairs, each pair comprising a square. Credit: Carter Roberts / Eastbay Astronomical Society.
Metcalfe said this discovery took a long time to verify, as the signature of this very small exoplanet was hard to confirm, to make sure the signature wasn’t coming from other sources such as an eclipsing binary star.
Kawaler said Kepler is sending astronomers photometry data that’s “probably the best we’ll see in our lifetimes,” he said, adding that this latest discovery shows “we have a proven technology for finding small planets around other stars.”
“We uncovered a planet smaller than any in our solar system orbiting one of the few stars that is both bright and quiet, where signal detection was possible,” said Thomas Barclay, lead author of Nature paper. “This discovery shows close-in planets can be smaller, as well as much larger, than planets orbiting our sun.”
And are there more small planets like this out there, just waiting to be found?
As the team wrote in their paper, “While a sample of only one planet is too small to use for determination of occurrence rates it does lend weight to the belief that planet occurrence increases exponentially with decreasing planet size.”
Despite advances in exoplanet research over the past decade much remains unknown. For example, how do the detection rates of giant planets vary as a function of the host star’s metal content? Are giant planets more frequent around massive stars? Do giant planets form under different mechanisms depending on the star’s metal content?
To that end a team of astronomers led by Annelies Mortier and Nuno C. Santos explored what mathematical function characterizes the detection rate across a distribution of stars (i.e., from metal-rich to metal-poor objects). “Finding the exact functional form of the metallicity-planet detection frequency will foster our understanding of both planet formation and the number of planets roaming the galaxy,” Santos told Universe Today.
Giant planets are most often found around metal-rich stars, and a figure from the team’s study (shown below) reaffirms that ~25% of stars featuring twice the Sun’s metal content host a giant planet, while the probability falls to ~5% for stars with a metal content analogous to the Sun.
Establishing that metal-rich stars exhibit an increased probability of hosting a giant planet constrains planet formation models. Specifically, the observations suggest that larger metallicity promotes the growth of rocky/icy cores, which subsequently accrete gas. However, the team notes that although the giant planet-metallicity trend is solid for stars exhibiting metallicities greater than (or analogous to) the Sun, the results are less certain for metal-poor stars. Indeed, there is an active debate in the literature pertaining to what function links the metal-rich and metal-poor regimes. In particular, does an exponential decline extend into the metal-poor regime, or does the function level off?
Depending on the manner in which the frequency trend extends into the metal-poor regime, it may indicate that a separate mechanism is responsible for creating that subsample’s giant planets. Thus continued surveys of metal-poor stars are important, despite the decreased frequency of finding a giant planet. Moreover, Mortier (Centro de Astrofisica, Universidade do Porto) notes that, “Studying metal-poor stars should be encouraged, since several theoretical models show that Earth-like planets are more common around these stars than around their metal-rich counterparts.”
Frequency of giant planets as a function of metallicity (credit: Mortier et al., arXiv 1302.1851).
The team focused their efforts on trying to discern a difference between the viability of various functional forms in the metal-poor regime (i.e., does the detection rate of giant planets in that domain flatten, rather than decline exponentially?). In the end no statistical difference was found between the scenarios, and it was likewise unclear whether a mass-dependence exists behind the frequency of giant planet detections. The team noted that a larger sample was needed to reach definitive conclusions, and added that ongoing surveys to discover planets would ensure the problem may soon be resolved.
“Kepler and Gaia will significantly increase the amount of planet discoveries, not only for giant planets, but also for smaller planets,” said Mortier.
In sum, to answer the questions posed at the outset planet-hunting efforts should be focused on metal-poor and metal-rich stars, despite the former exhibiting a reduced frequency of giant planets. The team’s findings will appear in Astronomy & Astrophysics, and a preprint is available on arXiv. The results from the study are tied in part to observations acquired via the HARPS (High Accuracy Radial Velocity Planet Searcher) instrument, which is shown below.
A new study estimates that fewer than 1% of transiting exoplanet systems host civilizations technologically advanced enough to send out radio transmissions that could be detected by our current SETI searches.
That equates to less than one in a million stars in the Milky Way Galaxy that would have intelligent life we could possibly communicate with. But even with those odds, there could be millions of advanced ET’s in the galaxy that we could phone, researchers say.
A group of astronomers, including Jill Tarter from the SETI Institute and scientists at the University of California, Berkeley used the Green Bank Telescope in West Virginia to look for intelligent radio signals from planets around 86 of stars where the Kepler mission has found transiting exoplanets. These specific targets were chosen because they had exoplanets in the habitable zone around the star and there were either five or more exoplanets in the system, or there was super-Earths with relatively long orbits.
The search came up empty in detecting any signals.
“We didn’t find ET, but we were able to use this statistical sample to, for the first time, put rather explicit limits on the presence of intelligent civilizations transmitting in the radio band where we searched,” said Andrew Siemion from UC Berkeley.
The team looked for signals in the 1-2 GHz range which is the region we use here on Earth for our cell phones and television transmissions. Narrowing it down, the team looked for signals that cover no more than 5Hz of the spectrum since there is no known natural mechanism for producing such narrow band signals.
“Emission no more than a few Hz in spectral width is, as far as we know, an unmistakable indicator of engineering by an intelligent civilization,” the team said in their paper.
The telescope spent 12 hours collecting five minutes of radio emissions from each star. Most of the stars were more than 1,000 light-years away, so only signals intentionally aimed in our direction would have been detected. The scientists say that in the future, more sensitive radio telescopes, such as the Square Kilometer Array, should be able to detect much weaker radiation, perhaps even unintentional leakage radiation, from civilizations like our own.
The researchers said these results allows them to put limits on the likelihood of Kardashev Type II civilizations. The Karashev scale is a method of measuring a civilization’s level of technological advancement, based on the amount of energy a civilization is able to utilize. The team said that finding no signals implies that the number of these civilizations that are “noisy” in the 1-2GHz range must less than one in a million per sun-like star.
The team plans more observations with the Green Bank Telescope, focusing on multi-planet systems in which two of the planets occasionally align relative to Earth, potentially allowing them to eavesdrop on communications between the planets.
“This work illustrates the power of leveraging our latest understanding of exoplanets in SETI searches,” said UC Berkeley physicist Dan Werthimer, who heads the world’s longest running SETI project at the Arecibo Telescope in Puerto Rico. “We no longer have to guess about whether we are targeting Earth-like environments, we know it with certainty.”
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.)
CfA 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)
Artist's concept of Kepler in action. NASA/Kepler mission/Wendy Stenzel.
There has been some concern about the Kepler spacecraft after one of the devices that provide the ability for super-precise pointing began misbehaving. Reaction wheels are devices which aim a spacecraft in different directions without firing rockets or jets, which reduces the amount of fuel a spacecraft needs; Kepler has four of them. Earlier this year, elevated friction was detected in reaction wheel #4, and so as a precaution for wheel safety, and as a measure to mitigate the friction, the reaction wheels were spun down to zero-speed and the spacecraft was placed in a thruster-controlled safe mode.
But now after a “rest” of the wheels for ten days, Kepler has now returned to science data collection beginning on January 28, 2013, and reaction wheel #4 seems to be operating normally, for now. During the 10-day resting safe mode, daily health and status checks with the spacecraft using NASA’s Deep Space Network were normal.
This is of special concern because last year, reaction wheel #2 failed. Kepler scientists say the spacecraft needs at least three wheels must operate until at least 2016 for Kepler to achieve its prime objective of finding Earth-like planets around sun-like stars. Last year, NASA approved an extended mission for Kepler through 2016, and so a lot is riding on the health of the spacecraft’s reaction wheels.
During much of the mission, ground controllers have observed intermittent friction on wheel # 4. Wheel # 2, on the other hand, showed no problems until early 2012, and it failed several months later.
“Since the failure of reaction wheel #2 in July 2012, the performance of the spacecraft on three wheels has been excellent,” said Kepler Project Manager Roger Hunter, writing an update on the Kepler website, noting that when reaction wheel #2 began to fail, it also exhibited elevated and somewhat chaotic friction.
“Reaction wheel #4 has been something of a free spirit since launch, with a variety of friction signatures, none of which look like reaction wheel #2, and all of which disappeared on their own after a time,” Hunter said. “Resting the wheels can provide an opportunity for the lubricant in the bearings to redistribute and potentially return the friction to nominal levels. Over the next month, the engineering team will review the performance of reaction wheel #4 before, during, and after the safe mode to determine the efficacy of the rest operation.”
As Emily Lakdawalla noted in one of the Weekly Space Hangouts, engineers are getting creative in how to deal with hardware issues in spacecraft, and compared the Kepler team’s approach to “resting” the reaction wheel to how engineers working with the Spirit Mars rover came up with the plan to have the rover drive backwards when one of the wheels started acting up, and the lubricant lasted longer when the wheel was used in the opposite direction.
Engineers for Kepler have implemented additional procedures to extend the lives of the reaction wheels, including running the wheels at warmer temperatures and alternating their spin directions.
Kepler was launched in March 2009, and is in an Earth-trailing solar orbit. It is pointed toward constellations Cygnus and Lyra, observing a 10-degree-wide field containing at least 4.5 million stars. Kepler is focusing on approximately 156,000 stars for the purposes of its research. Kepler scientists have found 105 new planets around other stars, and the mission’s data archive has evidence for more than 2,700 planet candidates.
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.
What 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.
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.
Artistic rendition of a sunset view
from the perspective of an imagined Earth-like moon orbiting the giant planet, PH2 b. Image Credit: H. Giguere, M. Giguere/Yale University
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.”
