Long-time Centauri Dreams readers will be familiar with the work of Manoj Joshi and Robert Haberle. Back in the 1990s when both were at NASA Ames (Joshi is now at the University of Reading), the scientists went to work on the question of whether planets around red dwarf stars could be habitable, given the problem of close orbits and tidal lock. Simulating the atmosphere of such a planet, they found even a thin atmosphere would circulate globally, moving enough heat to prevent the air on the darkside from freezing out. The prospect of a planet with oceans and a climate mild enough to support life began to look more promising. Joshi and Haberle have a new paper out that looks once again at planets around red dwarfs, this time extending the possible habitable zone to a greater distance from the star. M-class red dwarfs are smaller and cooler than G-class stars like the Sun, and emit a much larger fraction of their radiation at longer wavelengths where the reflectivity of ice and snow...

Imaging an Earth-like planet in the habitable zone may happen some time in the next decade if the James Webb Space Telescope can make its way through its budgetary hurdles and achieve a 2018 liftoff. But the word 'imaging' is a bit deceptive when you consider that we won't be getting anything remotely like the view of a planet in our own Solar System through Webb's instruments. No small disc with discernible features, in other words, but a single dot useful not because of what we can pick out visually, but because we can use its light to take a spectrum. And if we're really lucky, we'll find a dot that's blue and a spectrum that shows the signature of a living world. The JWST works at infrared wavelengths (covering a range from 0.6 to 28 micrometers), which is why shielding it from heat is so important, and why the design is marked by a large sunshield. These wavelengths should allow the instrument to study stars and galaxies from the early universe, but the addition of a starshade...

An orange dwarf star a bit smaller than our Sun is giving us valuable clues about how water-covered planets like Earth may evolve. TW Hydrae is 176 light years away, so young (5 to 10 million years) that it is still in the early stages of forming a planetary system. Working with data from ESA's Herschel space observatory, astronomers have found cold water vapor in the disc of dust and gas that surrounds the star. It's a significant find, because while we've found warmer water vapor in proto-planetary discs closer to their star, we now see evidence for much larger amounts of water in the outer disc, where the material for icy comets is found. Current theory holds that water will be far scarcer in the inner solar nebula around a coalescing system, meaning extensive oceans would have to be delivered by impacting objects from the outer regions. The Herschel data show the distinct signature of water vapor, probably produced when ultraviolet radiation from the central star warms ice-coated...

I've put off writing about Wesley Traub's paper on the frequency of planets in the habitable zone because I knew Adam Crowl had reservations about Traub's method. We talked about this at the 100 Year Starship Symposium, which led to Adam's agreeing to writing this piece for Centauri Dreams. How you define a habitable zone is, of course, a critical matter, especially when you're dealing with a topic as compelling as extrasolar planets that can support life. Adam places Traub's work in the context of earlier attempts at defining the habitable zone and finds HZ estimates different from Traub's, though one is surprisingly similar to a much earlier study. by Adam Crowl The recent paper by Wesley Traub [reference below] has estimated the frequency of terrestrial ("Earth-like") planets in the Habitable Zone (HZ) of their stars based on statistical analysis of the recent Kepler data release, but the frequency computed, of ~34(+/-14)% around FGK stars, is dubious due to the assumption of...

Three planets recently discovered through Kepler data provide an interesting take on how we look at smaller planets. Not that the planets around the star designated Kepler-18 are all that small -- two of them are Neptune-class and one is a super-Earth. But what is becoming clear is that given the state of our current technology, we'll have to get used to a process different from planet verification as we move to ever smaller worlds. The technique is being referred to as planet validation -- it helps us determine the probability that the detected object could be something other than a planet. Image: The orbits of the three known planets orbiting Kepler-18 as compared to Mercury's orbit around the Sun. Credit: Tim Jones/McDonald Obs./UT-Austin. The new system shows how this works. Kepler-18 is a star similar to ours, about 10 percent larger than the Sun and with 97 percent of the Sun's mass. Around it we have Kepler-18 c and d, which turn up through transits. Planet c has a mass of...