If, as we have often speculated in these pages, there is a brown dwarf closer to us than the Centauri stars, it may well be the WISE mission that finds it. The Wide-field Infrared Survey Explorer is a 40 cm telescope cooled below 17 K (-430 Fahrenheit) that will image the entire sky in four infrared wavelengths. If we're looking for nearby brown dwarfs, an all-sky survey like this is the way to go, because such stars should be distributed uniformly in the space around us. According to information Amanda Mainzer (JPL) presented yesterday at the American Astronomical Society meeting in Long Beach (CA), brown dwarfs are now thought to make up two-thirds of the stars in our stellar neighborhood, most of them as yet undetected. One of them might well be closer than the 4.3 light years that separate us from Alpha Centauri. And WISE should be up to the challenge of finding it, being able to detect cool brown dwarfs (down to 200 K) at Centauri distance and objects down to Jupiter-mass if...

The American Astronomical Society meeting now in session in Long Beach (CA) is already making news. Led by Michael Jura (UCLA), a team of scientists has used Spitzer Space Telescope data to study six white dwarf stars that are surrounded with the remains of asteroids. The assumption here is that these materials are a likely indication of planetary formation in these systems, for they're the same materials that go into making up the Earth and other rocky worlds in our own Solar System. "If you ground up our asteroids and rocky planets, you would get the same type of dust we are seeing in these star systems," says Jura, who presented the results at the meeting this morning. "This tells us that the stars have asteroids like ours -- and therefore could also have rocky planets." When a star like our Sun reaches the end of its life and becomes a red giant, it consumes any inner planets and perturbs the orbits of the surviving planets and asteroids. A white dwarf is the end result of this...

The title of yesterday's post -- 'The Odds on Centauri' -- would fit well with today's musings. Alpha Centauri makes us ponder the odds not just in terms of interstellar bets and future space probes, but also in terms of the likelihood of life around these stars. And after all, 2008 saw significant work on this question, including the contributions of Philippe Thébault (Stockholm Observatory) and colleagues, whose studies of Centauri A and B show that while stable planetary orbits exist there, the odds on those planets forming in the first place are long. Greg Laughlin (UC-Santa Cruz) isn't necessarily daunted by this work (he explains why here), but the planet-hunter extraordinaire is realistic about life-bearing planets in this environment, and even more judicious about the possibility of a technological society making its home in the system. The question rises naturally out of recent publicity given the 20th Century Fox film The Day the Earth Stood Still, in which it was...

A new camera called OPTIC (Orthogonal Parallel Transfer Imaging Camera), built at the University of Hawaii, has clarified our view of the distant world known as WASP-10b. Transits are helpful because they allow us to measure the size of the observed planets, and in this case, WASP-10b turns out to be not one of the most bloated exoplanets yet found, as once thought, but one of the densest. Orbiting some 300 light years from Earth, the planet's diameter is now known to be only six percent larger than Jupiter's, although it is three times more massive, with a corresponding density three times that of Jupiter. OPTIC is mounted on the University of Hawaii's 2.2-meter telescope on Mauna Kea. If you compare what it can do with its highly sensitive and stable detector to the best results from charge-coupled devices (CCDs), you find a photometric precision two to three times higher. According to this news release from the university's Institute for Astronomy, that's comparable to the most...

The Kepler mission launches March 5, a date to circle on your calendar. Kepler may become the first instrument to detect an Earth-size planet in the habitable zone of another star, using the transit method to examine 100,000 stars in its 3.5 year mission. The 0.95-meter diameter telescope is now at Ball Aerospace & Technologies (Boulder, CO), having passed the necessary environmental tests that demonstrate its space-worthiness. And word has just come that it has also passed the necessary 'pre-ship review' for transit to Florida in January. Image: An artist's rendering of what our galaxy might look like as viewed from outside. Our sun is about 25,000 light years from galactic center. The cone illustrates the neighborhood of our galaxy that the Kepler Mission will search to find habitable planets. Credit: Jon Lomberg. The image above, the work of the fine space artist Jon Lomberg, gives an idea of where Kepler will be looking. As always, Lomberg (creator of the gorgeous Galaxy Garden...

The nice thing about our conventional idea of a habitable zone is that liquid water can exist on the surface. The less helpful part of that definition is that water is more readily available much further out in a planetary system, where it usually shows up as ice. Think in terms of the 'ice line,' or the 'snow line.' Beyond it is the area around the still-forming star where temperatures are low enough to allow hydrogen compounds to condense into ice grains. Of course, we're living proof of the fact that planets in the inner system can be covered with oceans. It's therefore plausible to think in terms of delivery mechanisms, with icy comets bombarding planets in the inner system to produce oceans like those on Earth. But we're learning to extend our reach beyond conventional habitable zone notions to places much further out, an idea recently given credence by divers hands. Consider the work of Scott Gaudi (Ohio State), Eric Gaidos (University of Hawaii) and Sara Seager (MIT), familiar...

The prospect of habitable planets around red giant stars fires the imagination, enough so that quite a few readers forwarded me the link to a recent paper looking at this question. I'm reluctant to speak for others, but I suppose a major reason we're so interested (and I, too, had flagged the paper as soon as it popped up on the arXiv server) is that it changes our view of habitable worlds once again. Not long ago it was only the G-class, Sun-like star that seemed a likely abode of life. Then we started looking hard at M-dwarfs. Do we now extend the search to massive red giants, the descendants of stars once like our own? Image credit: NASA, ESA and A. Feild (STScI). Werner von Bloh (Potsdam Institute for Climate Impact Research) and team show that the possibility is real. We've long known that life on a planet in Earth's orbit would not survive the swelling of the Sun, even if it did not actually engulf the planet. But life on Earth would actually die out long before that event, if...

It's tantalizing to speculate that there might be a brown dwarf system nearer to us than the Alpha Centauri stars. The odds seem long, but the discovery of a pair of brown dwarfs that are each no more than a millionth as bright as the Sun makes for exciting reading. The objects were originally cataloged by the Two Micron All Sky Survey (2MASS) as a single brown dwarf identified as 2MASS J09393548-2448279, but Adam Burgasser (Massachusetts Institute of Technology) has been able to show that the 'object' is actually a pair of the faint dwarfs. Here the Spitzer Space Telescope was the instrument of choice, showing that 2M 0939's brightness was twice what would have been expected from its temperature, which was determined to be in the range of 565 to 635 Kelvin (560 to 680 degrees Fahrenheit). The implication was that this is a brown dwarf binary, two dwarfs each with a mass some thirty to forty times that of Jupiter. And while the objects are a million times fainter than the Sun in...

Among the many things that boggle my mind is the fact that we can learn things about the atmosphere of planets that we can't even see. Take well-studied HD 189733b, a gas giant in close orbit around a K2-class star some 63 light years from us. No one has ever laid eyes on this beast, either in infrared or optical light. But that's of little moment to the Hubble telescope, among whose tools is NICMOS -- the Near Infrared Camera and Multi-Object Spectrometer. It and a lot of ingenuity get results. A transiting planet like HD 189733b moves behind its parent star every two days or so. When that happens, light from the star itself (the planet now being behind the star) can be compared to the combined light of planet and star when both are facing the Earth. Any emissions from the planet can be examined, a useful window into its atmosphere. Using such techniques, Mark Swain (Jet Propulsion Laboratory) and team have been able to detect carbon dioxide and carbon monoxide on this world, which...

The Optical Gravitational Lensing Experiment has thus far rewarded researchers with twelve exoplanets, the most recent announced just today. OGLE's database is made up primarily of observations taken at the Las Campanas Observatory in Chile, its microlensing methods offering the chance to detect distant worlds that would be difficult if not impossible to study with radial velocity techniques. But because the project is all about parsing the light fluctuations of distant stars, OGLE has also found planets via the transit method, the most recent of them being the work of students at Leiden University in the Netherlands. OGLE2-TR-L9b is a discovery that points to the wealth of potential data on such worlds that may already exist in our databases. Thus the university's Ignas Snellen, who supervised the research project, found that the right software could tease a new planet out of OGLE data on some 15,700 stars, observed by the survey over a four year period between 1997 and 2000, even...

Images of distant exoplanets, once only a wish for future space missions, have begun to turn up with a certain regularity. The three planets around HR8799 and the single gas giant around Fomalhaut were announced on the same day, while a week later we once again have Beta Pictoris in focus, a young star so well studied that images of its dust disk go back to the mid-1980s. A new analysis of 2003 data from the Very Large Telescope now brings a team of French astronomers to offer a probable -- but not certain -- image of what may turn out to be Beta Pictoris b. The observations seem to show a gas giant some eight times more massive than Jupiter, orbiting at roughly 8 AU, not far inside Saturn's orbit in our own Solar System. But astronomer Gael Chauvin (Laboratoire d’Astrophysique de l’Observatoire de Grenoble) is quick to qualify the finding: "We cannot yet rule out definitively, however, that the candidate companion could be a foreground or background object. To eliminate this very...

The images of planets around Fomalhaut and HR8799 carried more clout than I expected, with traffic to the site quadrupling when the story ran, and substantial coverage from major media outlets as well. I ran the exciting images of both stars and their companions, but because I enjoy astronomical artwork, I now want to include the visualization below, showing Fomalhaut b surrounded by a large ring of autumnal russet and gold. Note, too, the extensive debris disk surrounding the distant star. Orbiting every 872 years, Fomalhaut b lies some 2.9 billion kilometers inside that disk's inner edge. Credit: ESA, NASA, and L. Calcada (ESO for STScI). Greg Laughlin (University of California, Santa Cruz) was surprised at the even-handed media treatment of HR8799, considering the brightness of Fomalhaut ('A star with a name like a rocket'), not to mention the acknowledged skills of the Hubble Space Telescope's media office. But while HR8799 isn't exactly a household word, the faint object trumps...

Are we really moving beyond indirect detection methods to being able to produce actual images of extrasolar planets? Apparently so, as witness the first direct images of multiple planets around a normal main sequence star. And on the same day, we have the announcement of a visible light image of a Jupiter-class planet orbiting the star Fomalhaut, one suspected for several years because of the sharply defined inner edge of the dust belt around the star. A planet in an elliptical orbit affecting the debris disk had been thought to be offsetting the inner edge of the belt. Let's go to the planets found around the dusty young star HR8799 first. They range from seven to ten times the mass of Jupiter. Bruce Macintosh (Lawrence Livermore National Laboratory), one of the authors of a new paper on the achievement in Science Express, explains its significance: "Every extrasolar planet detected so far has been a wobble on a graph. These are the first pictures of an entire system. We've been...

Roughly twenty percent of all detected exoplanets are in binary systems, intensifying our interest in Alpha Centauri. Recent work, however, has been less than encouraging to those hoping to find one or more terrestrial worlds around these stars. Indeed, Philippen Thébault (Stockholm Observatory), Francesco Marzari (University of Padova) and Hans Scholl (Observatoire de la Côte d’Azur) have shown that in the case of Centauri A, the zone beyond 0.5 AU is hostile to the accretion processes that allow planets to form. Any terrestrial-class world that close to Centauri A would be excluded from the habitable zone, a region thought to extend from 1.0 to 1.3 AU around the star. The same team now goes to work on Centauri B, having pointed out in the earlier paper that the mathematical modeling it used there was unique to Centauri A and could not be applied indiscriminately to other systems, not even to the second star of the Centauri binary. The authors are targeting the phase of planetary...

Two asteroid belts around Epsilon Eridani? So we learned yesterday, a fascinating find and one I want to discuss today, but only after celebrating Epsilon Eridani itself. Can any star have a more interesting pedigree? This is one of the Project Ozma stars, the other being Tau Ceti, that Frank Drake targeted in the first attempt to listen in on extraterrestrial civilizations. The Centauri stars seemed less likely then, in an era when multiple systems were thought to be hostile to planetary formation. But Epsilon Eridani and Tau Ceti were both single, Sun-like stars, surely possible homes to planets not much different from ours. Or so we thought. We've since learned that Tau Ceti's chances as a home to flourishing civilizations are diminished by the likelihood of intense cometary bombardment, while Epsilon Eridani itself is young enough (850 million years) that any parallel with our own Solar System, where life has had billions of years to attain technology, breaks down. But these...

We're all interested in transiting planets smaller than the Neptune-sized Gliese 436b, and sure to find many of them as our methods improve. One day soon, via missions like COROT or the upcoming Kepler, we'll be studying planets close to Earth mass and speculating on conditions there. But here's a scenario for you: Suppose the first Earth-mass detection isn't of a planet at all, but a moon orbiting a much larger planet? That challenging scenario comes from David Kipping (University College London) in a new paper on the detection of such moons. I should be calling them 'exomoons,' the satellites of planets around other stars. It's reasonable enough to assume they're out there in the billions given the nature of our own Solar System. And compared to the multitude of giant planets found thus far, an Earth-mass exomoon in the habitable zone would seem to offer a far more benign environment for life. The trick, of course, is to pull off a detection, for most exomoons are going to be...

Directly imaging a terrestrial planet is going to be a tough challenge. Suppose you were thirty light years from the Sun, looking back at our star in the hope of seeing the Earth. You would face the problem that the Earth and its star show an angular separation of 100 milliarcseconds, a spacing so tiny that the far brighter Sun would render its third planet (and all the others) invisible. Indeed, in optical wavelengths the Earth is ten billion times less bright than the Sun. How to go about seeing it? Observing at other wavelengths offers some help. The Sun is only a million times brighter than the Earth in the mid-infrared, which is why our first glimpse of planets like ours will probably be in this range. And it may be that our first catch is not a mature, established planet potentially offering a habitat to living organisms. Instead, it may be a clump of molten rock still glowing brightly from the heat of formation. Even after surface magma solidifies -- and new work suggests this...

If the weather on Uranus, examined here yesterday, isn't exotic enough for your taste, consider the situation on Jupiter-class worlds around other stars. A 'hot Jupiter' orbiting extremely close to its star spawns weather like nothing we've ever experienced, as modeled by computer simulations coming out of the University of Arizona. And while we can't actually image these objects yet, we can certainly deduce a great deal about them from observations made during the times they transit their star. On that score, well-studied HD 189733b is an early example of pushing the envelope. Located 63 light years from Earth, this transiting planet orbits once every 2.2 days, scooting along a mere three million miles from its primary. Spitzer Space Telescope data culling variations in starlight during the frequent planetary transits have allowed us to peg daytime temperatures on worlds like these, usually in a range somewhere between 2000 and 3000 degrees Fahrenheit (1300 and 1900 degrees Kelvin)....

How tides affect habitability has become a sub-genre within exoplanetary studies, a theme pushed hard by the gifted trio of Brian Jackson, Rory Barnes and Richard Greenberg (University of Arizona). You may want to browse through earlier Centauri Dreams entries on their work, especially this fascinating take on habitability around M dwarfs, in which the authors consider the possibility that Gliese 581 c was once a relatively benign place, but is now in an orbit that renders life impossible. Orbital evolution is the broad issue, sustained complex life demanding planets with low eccentricities. And orbital evolution can take a lot of time to operate. Now I see that Brian Jackson has presented new work on tides and habitability at the 40th annual meeting of the Division of Planetary Sciences in Ithaca, NY. Here we push into interesting questions about planets already inside a habitable zone that are nonetheless too hellish to support life, and planets outside that zone that seem too cold...

Computer simulations are showing us how to detect the signature of Earth-like planets -- indeed, planets nearly as small as Mars -- around other stars. That interesting news comes out of NASA's Goddard Space Flight Center, where a supercomputer named Thunderbird has been put to work studying dusty disks around stars similar to the Sun. Varying the size of the dust particles along with the mass and orbital distance of the planet, the team led by Christopher Stark (University of Maryland) ran 120 different simulations. "It isn't widely appreciated that planetary systems -- including our own -- contain lots of dust," Stark says. "We're going to put that dust to work for us." Indeed. Useful and observable things happen as dust responds to the forces acting upon it. For one thing, starlight can exert a drag that causes dust particles to move closer to the parent star. More to the point, particles spiraling inward can become involved in orbital resonances with planets in the system. A...