Conventional models of planet formation involve core accretion, where dust grains accumulate into protoplanets whose subsequent collisions and interactions produce planets, or gravitational instability, involving a rapid collapse from dense disk debris into a planetary core. But how far from the parent star does planet formation occur? The more we learn about protoplanetary disks, the more questions individual systems pose, as illustrated by the discovery highlighted today. I'm looking at the image of a young star called HD 142527 in the constellation Lupus, some 450 light years from Earth. The T Tauri star, some five million years old, is thought to be of about two solar masses. A team of Japanese astronomers using observations from the Atacama Large Millimeter/submillimeter Array (ALMA) has found an asymmetric ring of dust that appears, based on the density of dust in the densest part of the ring, to be producing planets. A previously discovered inner disk is confirmed by this...

2500 light years from Earth in the constellation of Cancer lies Messier 67, an open star cluster that is now known to be home to at least three planets. The new worlds, found using the HARPS spectrograph on the European Southern Observatory's 3.6-meter instrument at La Silla, come as the result of an observation program covering 88 selected stars in the cluster over a period of six years. The finding is noteworthy because we have so few known planets in star clusters of any kind. Moreover, one of these planets orbits a truly Sun-like star. Image: This wide-field image of the sky around the old open star cluster Messier 67 was created from images forming part of the Digitized Sky Survey 2. The cluster appears as a rich grouping of stars at the centre of the picture. Credit: ESO/Digitized Sky Survey 2 / Acknowledgement: Davide De Martin. I'm cautious about calling anything 'Sun-like' given how loosely that term has been used over the years, but ESO astronomers say the cluster star...

"Weather on Other Worlds" is an observation program that uses the Spitzer Space Telescope to study brown dwarfs. So far 44 brown dwarfs have fallen under its purview as scientists try to get a read on the conditions found on these 'failed stars,' which are too cool to sustain hydrogen fusion at their core. The variation in brightness between cloud-free and cloudy regions on the brown dwarf gives us information about what researchers interpret as torrential storms, and it turns out that half of the brown dwarfs investigated show these variations. Given the chance nature of their orientation, this implies that most, if not all, brown dwarfs are wracked by high winds and violent lightning. The image below could have come off the cover of a 1950's copy of Astounding, though there it would have illustrated one of Poul Anderson's tales with Jupiter as a violent backdrop ("Call Me Joe" comes to mind). Brown dwarfs are, of course, a much more recent find, and in many ways a far more...

As the 223rd meeting of the American Astronomical Society continues in Washington, we're continuing to see activity on the subject of mini-Neptunes and 'super-Earths,' the latter often thought to be waterworlds. Given how fast our picture of planets in this domain is changing, I was intrigued to see that Nicolas Cowan (Northwestern University) and Dorian Abbot (University of Chicago) have come up with a model that allows a super-Earth with active plate tectonics to have abundant water in its mantle and oceans as well as exposed continents. If Cowan and Abbot are right, such worlds could feature a relatively stable climate even if the amount of water there is far higher than Earth. Focusing on the planetary mantle, the authors point to a deep water cycle that moves water between oceans and mantle, a movement made possible by plate tectonics. The Earth itself has a good deal of water in its mantle. The paper argues that the division of water between ocean and mantle is controlled by...

Yesterday's look at the exoplanet KOI-314c showed us a world with a mass equal to the Earth, but sixty percent larger than the Earth in diameter. This interesting planet may be an important one when it comes to studying exoplanet atmospheres, for KOI-314c is a transiting world and we can use transmission spectroscopy to analyze the light that passes through the atmosphere as the planet moves in front of and then behind its star. A space-based observatory like the James Webb Space Telescope should be able to tease useful information out of KOI-314c. But the American Astronomical Society meeting in Washington DC continues, and it's clear that the technique of studying transit timing variations (TTV) is coming into its own as a tool for exoplanet investigation. David Kipping and colleagues use TTV to look for exomoons, and it was during such a search that they discovered KOI-314c. But consider the other AAS news. At Northwestern University, Yoram Lithwick has been measuring the masses...

'Exomoons' -- moons around planets around other stars -- are another of those new frontiers of modern astronomy. It's astonishing to reflect that 51 Pegasi b, the first exoplanet orbiting a main-sequence star, was discovered as recently as 1995, a time when we could only suspect that planets might be common and were only then working out the best ways to find them. Now we have thousands of planet candidates, the search is on for true Earth analogues, and the idea that we might make as fine-grained a discovery as an exomoon is an exhilarating prospect. So is the recent paper from David Bennett (University of Notre Dame) and colleagues the breakthrough we've been waiting for? The answer is no because we have no way of knowing whether this suggestive find is a true moon around a planet or perhaps two larger objects in gravitational synch at a much further distance. But either case is intriguing. Here are the possibilities for the 2011 event called MOA-2011-BLG-262, detected by...

Let me offer best wishes for the holidays to all Centauri Dreams readers, with thanks for the numerous comments and suggestions over the course of the past year. The schedule this week is abbreviated but I'll have a new post up on Friday. I'm about to set out to gather the materials I need for a family dinner tonight, but I have time this morning to talk about interesting new work on figuring out the mass of an exoplanet. As you might guess, this is a key measurement, and a tough one to make. The work out of MIT offers an elegant solution. I yield to no one in my admiration for the tough-minded Sara Seager (MIT), whose career in astrophysics is so movingly described in Lee Billings Five Billion Years of Solitude: The Search for Life Among the Stars. A number of readers pointed out Seager's most recent study, which develops this new technique for our exoplanet toolkit. Julien de Wit, a MIT grad student who is lead author on the paper just published in Science, describes his work with...

It was only in October of this year that we discovered that a red dwarf star called LP 876-10 was in fact part of the Fomalhaut system. Now known as Fomalhaut C, the diminutive object is making news of its own with the announcement that, like its much larger and brighter counterpart, Fomalhaut A, it hosts a belt of comets. That two stars in the same system could each have a ring of comets raises interesting issues. Grant Kennedy (University of Cambridge), whose team made the discovery using data from the Herschel Space Observatory, explains: "It's very rare to find two comet belts in one system, and with the two stars 2.5 light years apart this is one of the most widely separated star systems we know of. It made us wonder why both Fomalhaut A and C have comet belts, and whether the belts are related in some way." Image: View of the Fomalhaut triple star system from Earth. The small inset shows a zoom of the newly discovered comet belt around Fomalhaut C as seen at infrared...

Has astrometry finally bagged an exoplanet? A new study from Henri Boffin (European Southern Observatory) and colleagues has found compelling evidence that the nearest pair of brown dwarfs to the Sun -- WISE J104915.57-531906, otherwise known as Luhman 16AB -- is home to a hitherto undetected companion. It's interesting news not only for the astrometry angle but because Luhman 16AB is no more than 6.6 light years away, making it the third closest system to the Sun after Alpha Centauri and Barnard's Star. Image: Luhman 16AB, two brown dwarfs in the Sun's neighborhood, now considered home to a possible planet. Credit: NASA / JPL / Gemini Observatory / AURA / NSF. I give prominence to astrometry here because the European Space Agency's Gaia mission was launched this morning, chartered with creating a three-dimensional map of the Milky Way, but also with finding exoplanets using astrometry as its primary method. While radial velocity measures tiny motion in stars induced by unseen...

When the pace of discovery is as fast as it has been in the realm of exoplanet research, we can expect to have our ideas challenged frequently. The latest instance comes in the form of a gas giant known as HD 106906 b, about eleven times as large as Jupiter in a young system whose central star is only about 13 million years old. It's a world still glowing brightly in the infrared, enough so to be spotted through direct imaging, about which more in a moment. For the real news about HD 106906 b is that it's in a place our planet formation models can't easily explain. Image: This is a discovery image of planet HD 106906 b in thermal infrared light from MagAO/Clio2, processed to remove the bright light from its host star, HD 106906 A. The planet is more than 20 times farther away from its star than Neptune is from our Sun. AU stands for Astronomical Unit, the average distance of the Earth and the Sun. (Image: Vanessa Bailey). Start with the core accretion model and you immediately run...

Never give up on a spacecraft. That seems to be the lesson Kepler is teaching us, though it's one we should have learned by now anyway. One outstanding example of working with what you've got is the Galileo mission, which had to adjust to the failure of its high-gain antenna. The spacecraft's low-gain antenna came to the rescue, aided by data compression techniques that raised its effective data rate, and sensitivity upgrades to the listening receivers on Earth. Galileo achieved 70 percent of its science goals despite a failure that had appeared catastrophic, and much of what we've learned about Europa and the other Galilean satellites comes from it. Image: Galileo at Jupiter, still functioning despite the incomplete deployment of its high gain antenna (visible on the left side of the spacecraft). The blue dots represent transmissions from Galileo's atmospheric probe. Credit: NASA/JPL. Can we tease more data out of Kepler? The problem has been that two of its four reaction wheels,...

Thinking about the Kepler results now under discussion in these pages, one thing that stands out is that for most of the Kepler planets, we have no idea of their density. A transit can tell you about the size of the planet crossing in front of its star, but following up the detection with ground-based telescopes is crucial, because radial velocity studies can put some boundaries on its mass. With both size and mass in hand, you can determine the density, and that tells us whether a detected world is rocky like the Earth or a water world or an ice giant like Neptune. In a recent interview with Popular Mechanics, David Latham (Harvard-Smithsonian Center for Astrophysics) described TESS, the Transiting Exoplanet Survey Satellite, and its role in the planet hunt beyond Kepler. With so many space observatories either cancelled (Space Interferometry Mission) or on indefinite hold (Terrestrial Planet Finder), it's heartening to have this mission in the pipeline. And because TESS is going to...

The widely circulated Kepler results, announced yesterday, tell us that over twenty percent of Sun-like stars in the Milky Way have Earth-sized planets in the habitable zone, where liquid water could exist on the surface. Work out the math and it turns out that the nearest Sun-like star with a planet like ours in the habitable zone is probably on the order of twelve light years away, an energizing thought for those of us who ponder future technology and interstellar probes. Imagine: One in five Sun-like stars with a planet the size of Earth in the zone where liquid water can exist. Image: Analysis of four years of precision measurements from Kepler shows that 22±8% of Sun-like stars have Earth-sized planets in the habitable zone. If these planets are as prevalent locally as they are in the Kepler field, then the distance to the nearest one is around 12 light-years.zone. Credit: Petigura/UC Berkeley, Howard/UH-Manoa, Marcy/UC Berkeley. But how did we get here? Kepler, which was...

When I was first learning about astronomy by reading every book I could find on the subject -- I spent a lot of time at the library in my youth -- I was fascinated to hear stories of a planet closer to the Sun than Mercury. The French scientist Urbain Le Verrier pondered the existence of such a world in the 19th Century, wondering if it wouldn't explain peculiarities in Mercury's orbit. When an amateur astronomer named Edmond Modeste Lescarbault claimed he had observed a transit of such a planet in 1859, Le Verrier's investigation satisfied him that the detection was legitimate. He went on to announce the discovery of the planet he dubbed Vulcan in Paris in 1860. Despite a string of other observing claims later in the century, the existence of Vulcan is now discounted, although the possibility of asteroids in tight solar orbits hasn't been ruled out. As for Mercury, it fell to Einstein to demonstrate that apparent anomalies in its orbit could be explained by his theory of General...

HD 21997 is a star in the southern constellation Fornax (the Furnace) that is yielding some surprising data about how planetary systems form. About 235 light years from Earth, the star is 1.8 times the mass of the Sun and is thought to be about thirty million years old. Observations by an international team using ESA’s Herschel Space Observatory and the Atacama Large Millimeter/sub-millimeter Array (ALMA) in Chile show a ring of material around the star that contains not only a good deal of gas but also the dust produced by the collision of planetesimals. Image: ALMA images of the disk around HD 21997. The left image shows the emission of cold dust grains, situated in a ring around the central star. The middle image displays the emission from carbon monoxide, and shows that gas can also be found closer to the star than dust. The right image depicts the velocity of the gas. The red-colored parts of the disk move away from us, while the blue-colored parts move towards us, indicating...

Habitable zones are always controversial. Bring up the classic definition of a zone where liquid water can exist on the surface and you run into queries about places like Europa, far outside the HZ in those terms but perhaps capable of supporting life beneath the ice. For that matter, exotic forms of life cannot be ruled out in settings like Titan, though they would be nothing like what we’re familiar with on Earth. Nonetheless, refining our methods to look for life on planets with liquid water is a rational way to proceed and we’re developing the needed tools. As we wait for those tools to be funded and built -- projects like Terrestrial Planet Finder are on indefinite hold -- we can continue to develop our theoretical models for living planets. On that score, Torrence Johnson (JPL) and colleagues have had interesting things to say lately. Johnson spoke at the American Astronomical Society Division of Planetary Sciences meeting in Denver earlier this month, addressing the question...

The red giant Kepler-56, some 3000 light years from the Sun, is telling us useful things about planetary alignments. The star is somewhat out of synch with the majority of Kepler targets to begin with. Most of these are unevolved stars near the main sequence, which are those most likely to produce systems in which a terrestrial world can be observed. But Kepler-56 has exhausted its hydrogen core and has evolved into a red giant. Two planet candidates have been identified here, orbiting in 10.5 and 21.4 days respectively. In fact, Kepler-56 turns out to be the most evolved star observed by Kepler with more than a single detected planet. I'm drawing this from the work of Daniel Huber (NASA Ames) who, with a large team of collaborators, has been studying an apparent anomaly in the Kepler-56 system: The rotation axis of the star is tilted about 45 degrees to our line of sight. The Kepler-56 result was a surprise, says Huber, "because we already knew about the existence of two planets...

The recent question raised here about conditions on a white dwarf planet provides a segue to the white dwarf GD 61 and the interesting results reported by astronomers at the Universities of Cambridge and Warwick. Relying on data from Hubble as well as Keck I and Keck II and NASA's FUSE telescope, the researchers have analyzed what they believe to be evidence for an asteroid or minor planet that once contained large amounts of water around the star. The water-rich object would have been knocked out of its orbit and subsequently shredded by by the star's gravitational force. Image: Artist impression of a rocky and water-rich asteroid being torn apart by the strong gravity of the white dwarf star GD 61. Similar objects in the Solar System likely delivered the bulk of water on Earth and represent the building blocks of the terrestrial planets. Credit & Copyright: Mark A. Garlick, Space-Art.co.uk/University of Warwick/University of Cambridge. GD 61 is some 150 light years from us, but...

Considering how much data it has accumulated, the Kepler mission will continue to serve us even if its ongoing operations have ceased. We’re now seeing some of its data used in conjunction with observatories like the Spitzer space telescope to tease out further information. Combine the two and we can examine distant worlds at multiple wavelengths, leading Paul Hertz, director of NASA’s Astrophysics Division, to say “We're at a point now in exoplanet science where we are moving beyond just detecting exoplanets, and into the exciting science of understanding them.” Exciting indeed, for what this multi-wavelength look has now provided is a low-resolution view of the clouds on one of Kepler’s earliest finds, the ‘hot Jupiter’ known as Kepler-7b. Spitzer has already proven its capabilities by producing temperature maps of exoplanets, but this is the first time we’ve been able to map cloud structures. The visible light Kepler observations had revealed a bright spot on the planet’s western...

Yesterday's look at Sara Seager's new equation pointed out that it was designed to estimate how many planets with detectable signs of life could be discovered in the near future. The interview Seager gave to Astrobiology Magazine contrasts her work with Frank Drake's famous equation to estimate the number of extraterrestrial cultures able to communicate with us. The comparison is understandable given the high visibility of Drake, but what I have called the Seager Equation is really something other than a revision of the earlier Drake principles. For Seager's focus is on the detection of any kind of life, not just communicating technological cultures, and her work is especially attuned to M-class dwarf stars, the kind of stars on which we're most likely to be able to perform the needed observations in the near term. The biomarkers we're looking for will probably first be examined by the James Webb Space Telescope, which will analyze the light from a parent red dwarf as a planet...