Kepler is a telescope that does nothing more than stare at a single patch of sky, described by its principal investigator, with a touch of whimsy, as the most boring space mission in history. William Borucki is referring to the fact that about the only thing that changes on Kepler is the occasional alignment of its solar panels. But of course Borucki's jest belies the fact that the mission in question is finding planets by the bushel, with more than 1200 candidates already reported, and who knows how many other interesting objects ripe for discovery. Not all of these are planets, to be sure, and as we'll see in a moment, many are intriguing in their own right. But the planets have center stage, and the talk at the American Astronomical Society's 218th meeting has been of multiple planet systems found by Kepler, after a presentation by David Latham (Harvard-Smithsonian Center for Astrophysics). Of Kepler's 1200 candidates, fully 408 are found in multiple planet systems. Latham told...

Gravitational microlensing to the rescue. We now have evidence for the existence of the rogue planets -- interstellar wanderers moving through space unattached to any star system -- that we talked about just the other day. It's been assumed that such planets existed, because early solar systems are turbulent and unstable, with planetary migrations like those that lead to 'hot Jupiters' in the inner system. Moving gas giants into orbits closer to their star would cause serious gravitational consequences for other worlds in the system, ejecting some entirely. But while we've been thinking in terms of detecting such worlds through auroral emissions like those produced by Jupiter, researchers at two microlensing projects have made a series of detections by using gravity's effects upon spacetime. Specifically, a stellar system passing in front of a far more distant background star will warp the light of the background object. The resulting magnification and brightening flags the presence...

Imagine a planet far more massive than Jupiter and spinning faster than Jupiter's 10 hour rotation. Throw in a large nearby moon and the associated auroral effects that would occur as the moon moved through fields of plasma trapped in the planet's magnetic field. The scenario isn't all that different from what we see happening between Jupiter and Io. But here's the kicker: Put planet and moon far away from any star, a rogue planet scenario of the kind recently discussed by Dorian Abbot and Eric Switzer, who called such rogue planets 'Steppenwolfs.' I jumped on that idea in a Centauri Dreams post last February because interstellar planets have always fascinated me. Abbot and Switzer were interested in whether a rogue planet could support life, finding in their paper that a planet just 3.5 times as massive as the Earth, and with the same basic composition and age, could sustain a liquid ocean under layers of insulating water ice and frozen atmosphere. But our rogue gas giant offers...

My friend Adam Crowl, a polymath if there ever was one, is working hard on Project Icarus and keeping an eye on the exoplanet situation. When you're working on a starship design, no matter how theoretical, a major issue is the choice of targets, and the study of Kepler planets we looked at yesterday caught Adam's eye some time ago. We're not finding as many planets in the habitable zone thus far in the Kepler hunt as we might hope to, given that the ideal would be a habitable world somewhere within reach of near-future technologies of the kind that Icarus represents. Sure, Kepler's target stars are much further away in most cases, but the mission is giving us a useful statistical sampling from which we can generalize. Working with the data from Lisa Kaltenegger and Dimitri Sasselov's paper, Adam thus takes a back-of-the-envelope stab at the galactic population of terrestrial worlds, knowing that Kepler is far from through, as we're moving into the domain of planets with longer...

A habitable zone can be defined in many ways, but for our immediate purposes, defining it with reference to liquid water on a planetary surface makes sense. Sure, we believe that life could exist beneath the surface on places like Europa, where surface water is out of the question, but the key issue is this: Are there atmospheric features that we could use to make the call on habitability? It's an important issue because with our current and near-future technology, this is how we can plan to investigate life on planets around other stars. We can study exoplanetary atmospheres already and we're getting better, but we can't drill through exoplanetary ice. A new paper from Lisa Kaltenegger and Dimitri Sasselov (Harvard Smithsonian Center for Astrophysics) gets into these questions by looking at how to evaluate habitability, studying different kinds of planetary atmospheres and developing model calculations. The intent is to apply these ideas to the habitable planet candidates, 54 in...

Over 900 stars have been found that show signs of a debris disk, a circumstellar disk of dust and debris orbiting the star. It takes less than 10 million years for the gaseous content of these disks to dissipate, leaving the dusty disk behind. You can think of the Kuiper Belt in our own system, but the analogy would be imprecise in a crucial way, for most of these disks show much more dust. In fact, explaining the difference between the debris disks of other stars and what we see in our own system is instructive, and it may offer clues to terrestrial planet formation elsewhere. For we're learning that long-lasting cold dust points to a system-wide stability that is probably crucial. At issue is the question of what happens when gas giants cause gravitational instabilities in a young system. Sean Raymond (Université de Bordeaux) and collaborators tackle the question in a new paper that looks at how planets emerge from circumstellar disks. Inner disks form rocky planets in 10 to...

We've been finding planets using radial velocity methods -- analyzing the gravitational effects of planets around their stars -- since the mid-1990s, and the Kepler mission has brought the transit method to the fore, looking at the lightcurves of stars when planets pass in front of them as seen from Earth. Now we have new information about a transiting planet, 55 Cancri e, in a multiple planet system, information that has been developed by reanalyzing earlier radial velocity data. The new techniques were applied by Rebekah Dawson (Harvard-Smithsonian Center for Astrophysics), working in tandem with Daniel Fabrycky (UC-Santa Cruz) to predict the orbit of 55 Cancri e. Earlier radial velocity data on the planet had suggested a tight orbit of 2.8 days, but the new analysis pegged the orbit at something less than 18 hours. The proximity to the central star meant that the chances of seeing a transit were higher than thought (the probability moved from 13 percent to 33 percent), leading to...