The COROT mission, to be launched in December, promises to move us to the next level of planetary detection. Devoted to studying exoplanet transits, in which a planet crosses the face of its star as seen from Earth, the space telescope will probably detect numerous 'hot Jupiters.' But an even more interesting possibility is rocky worlds in close orbit around their stars. And the thinking is that planets only a few times larger than Earth -- and perhaps even smaller than that -- will be within its reach. Any star with a transiting planet will provide a telltale drop in light that, depending on the size of the planet and the distance of the star, may be measurable. But COROT (the acronym stands for Convection Rotation and planetary Transits) is most sensitive to rocky worlds in orbits of 50 days or less. If that sounds dismaying in terms of habitability, consider that a planet in such an orbit around a dim red dwarf could be located ideally within the star's habitable zone. And red...

How could you possibly study the interior of a giant planet orbiting another star? Especially when that planet is so drowned in its star's light that we can't even see it? Various methods suggest themselves, including transits, those cases wherein the exoplanet happens to pass between us and the star it circles. A transit gives you the chance to measure both mass and size. Throw in inferences based on slowly evolving planetary models and you can draw some tentative conclusions. You also wind up with even more questions. And as Tristan Guillot would probably point out, we now have twenty gas giants whose mass and size can be determined, including those within our own Solar System. Guillot, who works in one of the most celestially beautiful places on Earth (he's at the Observatoire de la Cote d'Azur in Nice), makes it his business to compare and contrast what we see around Sol with the rising number of giant planets we're finding around other stars using the transit method. Several...

Watching the snowline descend to ever lower elevations as fall deepens into winter is one of the great pleasures of the Canadian Rockies, an area better suited to train travel than any on Earth. And an image of snow-topped mountains in Alberta came back to me as soon as I read about another kind of snowline, the boundary between the inner regions of a solar system, where rocky planets tend to form, and the outer depths, which become the domain of cold, gaseous worlds. The snowline holds clues to how 'super-Earth' planets form. The paper, by Grant Kennedy (Mt. Stromlo Observatory, Australia) and colleagues, takes a hard look at M-class red dwarfs and contrasts them to solar-type stars. The latter show a relatively constant luminosity during planet formation, meaning conditions change little during this era. But red dwarfs fade dramatically as they evolve toward maturity, dimming to the point where what had been a warm inner disk begins to freeze. And that has implications for...

Imagine being able to measure day and night temperatures on a planet circling another star. That's just what the Spitzer Space Telescope has managed, homing in on the atmosphere of Upsilon Andromedae b, a 'hot Jupiter' orbiting its parent star every 4.6 days. The results are, as you might expect for a planet this close to its star, extreme. The temperature difference between the two sides of this world is a whopping 1400 degrees Celsius (2550 degrees Fahrenheit). We're looking at a planet that seems to be tidally locked to the star it circles, but unlike other tidally locked objects like our Moon, this one has a thick atmosphere that could be circulating faster than the interior. The scientists behind this work are essentially doing meteorology, as witness this remark by Joe Harrington (University of Central Florida): "This planet has a giant hot spot in the hemisphere that faces the star. The temperature difference between the day and night sides tells about how energy flows in the...

The new planet discovered around the red dwarf GJ 849 isn't just another footnote in the unfolding story of exoplanet discoveries. This world, a gas giant about 80 percent as massive as Jupiter, promises to teach us more about planet formation around M-class stars, by far the most common stellar objects in the galaxy (with the possible exception of brown dwarfs). And the more we learn about the so-called core accretion model, the more we'll understand what to expect as we point our telescopes in the direction of other red dwarfs. Not bad for a planet circling one of the 152 stars within 200 parsecs of the Sun known to have planets. But bear this in mind: most of the stars around which we've found these planets have been like our Sun, in the range of 0.7 to 1.3 times its mass. We've studied over 200 M-class dwarf stars with planet detection in mind, but until now had discovered planets around only three. GJ 436 shows a Neptune-class world, as does GJ 581, while GJ 876 seems to be a...