I confess it had never occurred to me to consider cloud cover on exoplanets in quite the same light that a new study does. But two Spanish astronomers from the Astrophysical Institute of the Canary Islands (IAC) are taking a look at how clouds operate over different kinds of surfaces, in the process figuring out what our Earth would have looked like from space in different eras. It’s an interesting thought: Given the movement of Earth’s continents in the past 500 million years, what would cloud patterns have been like over land and sea as landforms changed? The researchers chose several times to study, from 90, 230, 340 to 500 million years ago, pondering how changes in light reflected from the Sun would have operated here and, by extension, how they might operate on distant exoplanets. We’ll need to keep these things in mind when we get the capability of studying the atmospheres of terrestrial planets around other stars. And it turns out that, according to the researchers, cloud...

Confirming Kepler's planet candidates is a crucial part of the process, because no matter how tantalizing a candidate appears to be, its existence needs to be verified. We have more than 60 confirmed Kepler planets and over 2300 candidates, many of which will eventually get confirmed, but it's interesting to see that the mission's latest announcements relate to multiple planet systems and how their presence can itself speed up the verification process. In today's focus are the eleven new planetary systems just announced, 26 confirmed planets in all, which actually triples the number of stars known to have more than one transiting planet. One of the systems, Kepler-33, has been demonstrated to have five planets. We also have five systems (Kepler-25, Kepler-27, Kepler-30, Kepler-31 and Kepler-33) showing a 1:2 orbital resonance -- the outer planet orbits the star once for every two orbits of the inner planet -- and four systems with a 2:3 resonance, with the outer planet orbiting twice...

What to say about an extrasolar ring system that has already had its four distinct rings named? Rochester, Sutherland, Campanas and Tololo are the Earth-bound sites where the unusual system was first detected and analyzed, and the international team of researchers involved thought them suitable monickers for the four rings thus far detected. The light curve of the young, Sun-like star they’ve been studying in the Scorpius-Centaurus association -- a region of massive star formation -- shows what appears to be a dust ring system orbiting a smaller companion occulting the star. The data here come from SuperWASP (Wide Angle Search for Planets) and the All Sky Automated Survey (ASAS) project. The star in question is 1SWASP J140747.93-394542.6, which displays a complex eclipse event with, at some points, 95 percent of the light from the star being blocked by dust. Similar in mass to the Sun, the star is only about 16 million years old, and lies about 420 light years away from the Solar...

Last week's meeting of the American Astronomical Society is still much in the news, and I want to cover several more stories from the Austin conclave this week, starting with yet another circumbinary planetary system, in which a planet orbits two stars. Not long ago we looked at Kepler-16b, a circumbinary planet orbiting two stars in this mode -- as opposed to a binary system where planets orbit one or the other of the two stars. Kepler-16b was interesting but perhaps unusual given the perceived difficulties in finding stable orbits around close binaries. But things are happening quickly on the exoplanet front. Needing more information about the prevalence of this kind of planet and the range of orbital and physical properties involved in such systems, we now get news of not one but two more, Kepler-34b and Kepler-35b. Note the nomenclature: We could as easily call these Kepler-34(AB)b and Kepler-35(AB)b. We confront the real possibility that 'two sun' systems are not necessarily...

Exomoons are drawing more interest all the time. It may seem fantastic that we should be able to find moons around planets circling other stars, but the methods are under active investigation and may well yield results soon. Now David Kipping (Harvard-Smithsonian Center for Astrophysics) and colleagues have formed a new project called HEK -- the Hunt for Exomoons with Kepler. We thus move into fertile hunting ground, for there has never been a systematic search for exomoons despite the work of ground-breaking researchers like Kipping, Gaspar Bakos (Princeton) and Jean Schneider (Paris Observatory). It’s definitely time for HEK as Kepler’s exoplanet candidate list grows. Kepler, of course, works with transit methods, noting the dip in starlight as an exoplanet passes in front of the star under observation. HEK will use Kepler photometry to look for perturbations in the motion of the host planet that could flag the presence of a moon. Variations in transit timing (TTV) and duration...

It’s always gratifying to note the contributions of amateur astronomers to front-line science. In the case of three small planets discovered around the Kepler star KOI-961, the kudos go to Kevin Apps, now a co-author of a paper on the new work. It was Apps who put postdoc Philip Muirhead (Caltech) on to the idea that KOI-961, a red dwarf, was quite similar to another red dwarf, the well-characterized Barnard’s Star, some six light years away in the constellation Ophiuchus. It was a useful idea, because we do have accurate estimates of Barnard Star’s size, and the size of the star becomes a key factor in exoplanet detections. For the depth of a light curve -- the dimming of the star over time due to the passage of planets across its surface as seen from Kepler -- reveals the size of the respective planets. Researchers from Vanderbilt University aided the Caltech team in determining KOI-961’s size, a difficult call because while Kepler offers data about a star’s diameter, that data is...

People sometimes ask why we are spending so much time searching for planets that are so far away. The question refers to the Kepler mission and the fact that the distance to its target stars is generally 600 to 3,000 light years. In fact, fewer than one percent of the stars Kepler is examining out along the Orion arm are closer than 600 light years. The reason: Kepler is all about statistics, and our ability to learn how common exoplanets and in particular terrestrial planets are in the aggregate. The last thing the Kepler team is thinking about is targets for a future interstellar probe. Studies of closer stars continue -- we have three ongoing searches for planets around the Alpha Centauri stars, for example. But there is so much we still have to learn about the overall disposition of planets in our galaxy. New work by an international team of astronomers involves gravitational microlensing to answer some of these questions, and the results suggest that planets -- even warm,...

The annual meeting of the American Astronomical Society is now in session in Austin, sure to provide us with interesting fodder for discussion in coming days. Just coming off embargo yesterday was news of further study of the interesting Kepler-16 system. This one made quite a splash last fall when the planet known as Kepler-16b was discovered to orbit two stars, with the inevitable echoes of Star Wars and the twin suns that warmed the planet Tatooine. This planet, though, was a gas giant more reminiscent of chilly Saturn than a cozily terrestrial world. Image: An artist's conception of the Kepler-16 system (white) from an overhead view, showing the planet Kepler-16b and the eccentric orbits of the two stars it circles (labeled A and B). For reference, the orbits of our own solar system's planets Mercury and Earth are shown in blue. New work out of the University of Texas at Arlington explores the question of habitability in a system like this. Credit: NASA/Ames/JPL-Caltech. You'll...