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...