Astrometry, using the position and motion of celestial objects to further astronomical research, is ever more useful in the study of extrasolar planets. If you can measure how much a given star is displaced by the presence of a planet, you have a valuable adjunct to existing radial velocity and transit methods. Now a new study has examined astrometry's uses with binary stars, using the Hale telescope on Mt. Palomar and the Keck II instruments on Mauna Kea. And with certain restrictions, adaptive optics may allow us to detect binary star planets. The targets were seventeen binary or multiple star systems, most of them M-dwarf binaries closer than 20 parsecs from the Sun. Observations were conducted in the near infrared, with relative separations and position angles carefully measured. Study authors Krzysztof Helminiak and Maciej Konacki (Nicolaus Copernicus Astronomical Center, Poland) note the advantage of close systems: The closure of companions allows one to observe visual binaries...

Finding transiting planets is no longer a surprise, and we can expect a host of transits from the CoRoT mission, which has the advantage of observing from a space-based platform. Moreover, CoRoT will, in the course of its lifetime, survey as many as 120,000 stars for up to five months. Driving home the advantage is the announcement of a new CoRoT planet known as CoRoT-Exo-4b. We're dealing with another Jupiter-sized planet orbiting in close proximity to its star, but this one has a unique claim to distinction: Its host star is rotating at the same pace as the planet's orbit. Image: Fixated upon a star: An artists impression of the satellite CoRoT in orbit around the Earth. Credit: CNES. Moreover, for a transiting world, CoRoT-Exo-4b is a relatively long-period planet, orbiting its F-class primary in 9.2 days. Thus far most transiting worlds have had orbits below about five days, two major exceptions being HD 147506b and HD 17156b, the latter with a period of 21.2 days -- both of...

You must see new video from EPOXI, whose effect can only be suggested by the photo montage below (click the link below for the movie). EPOXI is the combined extended mission of the Deep Impact spacecraft. As we discussed in an earlier story here, EPOXI turned its cameras on the Earth to view the moon transiting the planet's disk from a vantage point of 31 million miles. Think in terms of viewing the Earth the way we will eventually view terrestrial worlds around other stars. The idea is to build insights into how these worlds can be observed and characterized. Image: The moon crossing the Earth, as viewed by EPOXI. Video credit: Donald J. Lindler, Sigma Space Corporation/GSFC; EPOCh/DIXI Science Teams. Drake Deming (NASA GSFC), deputy principal investigator for EPOXI and leader of the extrasolar planet component of the mission (called EPOCh), points out how the information can be helpful: "Our video shows some specific features that are important for observations of Earth-like...

It's easy to see why interest in planets around red dwarfs is growing. The low mass of such a star makes finding smaller planets feasible. It also produces orbits closer to the star, another aid to their detection. We know that planets can form near the habitable zone of such stars because we have the example of Gliese 581, where two planets orbit close to if not just within that region. But is a habitable planet always habitable? If not, what could make these conditions change? I'm looking at a paper that examines tidal effects, an important factor when dealing with M dwarfs. Planets in the habitable zone around these stars experience effects that can cause both their orbital distance and orbital eccentricity to decrease [see comments below re my original misstatement of the eccentricity change, now corrected]. The paper, by Rory Barnes (University of Arizona, Tucson), Sean Raymond (University of Colorado, Boulder) and team, examines an interesting parameter: The habitable lifetime....

We've been paying a lot of attention to Centauri A and B in the past two years, but what about Proxima Centauri? After all, this is the closest star to our Sun, a fifth of a light year out from the two major Centauri stars, and free of the close binary problem. You would think this small red dwarf would rank higher on our list of astrobiologically interesting places, but until recently, that red dwarf status has been an encumbrance. It has been only within the last eleven years that the presumed tidal locking of planets in the habitable zone of such stars has been found not to be a necessary deterrent to the formation of a stable climate. Today, M dwarf interest grows. There's at least the chance of a workable ecosystem around such a star, assuming flare activity (common to these stars) might act more as an evolutionary stimulus than a deterrent to life. Moreover, the long lifetimes granted to M dwarfs mean that stable environments could exist for many billions -- perhaps hundreds of...

The news about planetary prospects around the Centauri stars has been positive enough lately that a paper suggesting otherwise introduces a rather jarring note (to me, at least). After all, we've detected more than forty extrasolar planets in multiple systems, a significant percentage of all detected exoplanets, and while most of these are in systems where the stars are widely spaced, there are planets around stars like Gliese 86 or Gamma Cephei where the separations are in the range of a Centauri-like 20 AU. Moreover, key studies have shown that planetary orbits in the habitable zone of the Centauri stars are viable. But what Philippen Thébault (Stockholm Observatory), Francesco Marzari (University of Padova) and Hans Scholl (Observatoire de la Côte d'Azur) bring to the table is a different question. Never mind that planetary orbits may be stable -- how likely are planets to form in these settings in the first place? It turns out that the last stage of planet formation has been...

We'd all like to think our Solar System is a run-of-the-mill place, filled with the kind of planets, including our own, likely to be found around other stars. But maybe it's not so ordinary after all. For recent work suggests that stars like the Sun aren't all that likely to form planets the size of Jupiter or larger. So while small, rocky worlds may or may not be common -- we're still finding the answer to that one -- the combination of rocky worlds and gas giants we take for granted may actually be distinctive. Once again I'm reminded how many conjectures go into our projections of habitable worlds. Here's one possibility: Without a large gas giant in the outer solar system to act as a gravitational shield for the inner system, planets in the habitable zone of a star might be so pelted by space debris that life would be unlikely to form on them. So it's conceivable that any findings about the scarcity of gas giants are a blow to our astrobiological hopes around other stars. At...