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...