Budding astrobiologists should be thinking about the significance of red dwarf stars as they approach their careers. Let's say, as pure speculation, that one out of every thousand stars in class M has a planet in the habitable zone. That works out to 75 million potentially habitable planets around these stars in our galaxy alone. Note the assumptions I'm making. First, I peg M dwarfs at 75 percent of the galactic population. That figure is widely in use and I've just run across it again in a new paper by Paul Shankland (US Naval Observatory), David Blank (James Cook University, Australia) and colleagues, about which more in a moment. Another assumption: That the Milky Way holds about one hundred billion stars. That's low-balling the number, I think, because estimates seem to start at that figure and go up to four or five times as high. So my 75 million potentially habitable planets, while just a guess, may not be totally off the wall. Image: An artist's impression of a gas giant...

I've never met George Ricker, but in at least one respect I believe he thinks the way I do. Ricker is senior research scientist at MIT's Kavli Institute for Astrophysics and Space Research, and he's someone who can connect the exoplanetary systems we study with places we might eventually go. As witness this comment in a discussion of a planned satellite-based observatory being designed at the Institute: "Decades, or even centuries after the TESS survey is completed, the new planetary systems it discovers will continue to be studied because they are both nearby and bright. In fact, when starships transporting colonists first depart the solar system, they may well be headed toward a TESS-discovered planet as their new home." It's wonderful to see a 'when' rather than an 'if' when referring to starships, even though everyone concerned can appreciate the blue-sky nature of the comment. For my part, I'll take whatever the physics will bear, from close-up imagery of terrestrial exoplanets...

The recent news that there may be an underground ocean on Titan tantalizes us in astrobiological terms. It also brings us up against the question of how to define a habitable zone. The standard definition involves the presence of liquid water at the surface, a reasonable requirement when you're looking for carbon-based life. But it's also true that exobiology may one day be studying forms of life that are nothing like us, living in environments we would at first dismiss from our list of living places. Just how far does a habitable zone extend? First, a short defense of the status quo. As we expand our exoplanet hunt and become capable of detecting the signature of life on distant planets, we need a target list to optimize our search time. It's entirely reasonable to fine-tune that list toward conditions similar to what we find on Earth because the life on our planet is the only kind we've been able to study. Detecting its biomarkers in an alien atmosphere is a sensible goal. We know...

Well-studied HD 189733b is a Jupiter-sized planet again in the news. Studying this transiting world, scientists using Hubble Space Telescope data have made the first identification of an organic molecule -- methane -- in the atmosphere of an exoplanet. What's particularly significant here is the growing sophistication of our use of spectroscopy, splitting light into its components to tease out the constituents of the atmosphere under study. This new finding shows that we're on target in planning to use space-based observatories to make far more challenging detections. Image: A wide field image of the region of sky in which HD 189733b is located. In this image we can see the asterism of the "Summer Triangle" a giant triangle in the sky composed of the three bright stars Vega (top left), Altair (lower middle) and Deneb (far left). HD 189733b is orbiting a star very close to the centre of the triangle. Credit: A. Fujii. Methane in the atmosphere of a gas giant wouldn't rank as a...

We have interesting news coming up this week with regard to the first detection of methane in the atmosphere of an exoplanet, of significance because it demonstrates that we can detect organic molecules using spectroscopy in ways that will one day help us study the atmospheres of terrestrial worlds around other stars. More on this later in the week, after a NASA teleconference scheduled for the 19th. Today, though, let's talk about another kind of detection in the circumstellar disk of a young star. At work in the latter is the Spitzer Space Telescope's infrared spectrograph, which is being put to use to look at the composition of protoplanetary disks. Specifically, John Carr (Naval Research Laboratory) and Joan Najita (National Optical Astronomy Observatory, Tucson) have been examining gases in the planet forming region around the star AA Tauri, using refined methods that have allowed them to find the spectral signatures of three organic molecules: Hydrogen cyanide, acetylene and...

Keep your eye on Gliese 581. Not that the news is necessarily good for our hopes for habitability around that star -- in fact, a recent paper suggests quite the opposite. The red dwarf exploded into the public consciousness with the announcement that one of its planets -- Gl 581 c -- could conceivably support clement temperatures and water at the surface, at least in places. But in exploring that possibility, we're getting a case study of world-class science at work, analyzing data, offering hypotheses, broadening options. It's an exciting process to watch. Gl 581 d is now being analyzed for habitability, while Gl 581 c begins to appear less and less likely as a home to life. It may take decades and new space-based observatories for the issue to be resolved, but we now have a new take on Gl 581 c, embedded in a broader study of tidal evolution as planetary systems evolve. The study has implications not just for rocky worlds but for planetary formation in many scenarios. The work of...

A new observing program designed to study planets around small, cool stars is in the works. TEDI, the TripleSpec - Exoplanet Discovery Instrument, saw first light on the 200-inch Hale Telescope just before Christmas, and is now in its commissioning phase, with an observing program scheduled to begin this spring. And for those who occasionally wonder why we seldom discuss stars like Barnard's Star or Proxima Centauri in terms of the planet hunt, read on. For TEDI is the kind of program that should be able to survey not just M dwarfs but L and T class stars as well, opening exciting possibilities for discovery. Planets around Proxima Centauri? Perhaps, and extending all the way down to T-class brown dwarfs makes things interesting as well. But finding such planets is a challenge with conventional radial velocity methods. Here's why: Radial velocity searches are generally conducted in the optical band, and work well with stars, like the Sun, that are bright at these wavelengths. The...