The COROT space telescope doesn't start scientific observations until February, but the protective cover of the 30 centimeter instrument has now been opened. So far so good. A preliminary calibration exercise -- using the constellation of the Unicorn near Orion -- delivers data of excellent quality. This news from the European Space Agency should keep exoplanet hunters primed as the search for transiting worlds takes to space. A diagram of COROT's interesting orbit can be found here.

Habitable planets in multiple star systems are one of science fiction's great tropes. Find a second star somewhere in the daylight sky and you know you're not in Kansas anymore. It makes slow going today, but as a kid I was struck with William F. Temple's The Three Suns of Amara (1962), a story whose questionable science and creaky plot was somewhat mitigated by its striking imagery. For Amara managed to weave its orbit through a triple star system in which each star was a different color. Talk about great visual effects! Image: My battered copy of Temple's The Three Suns of Amara, rescued from a closet. Not the best novel I've ever read, but it did instill a lifelong fascination with habitable planets in multiple star systems. Yesterday we looked at Elisa Quintana's work on habitable planets in binary systems, and while reviewing for that story, I found Temple's Amara again coming to mind. For it turns out we do have five confirmed exoplanets known to orbit one member of a triple...

The findings about possible terrestrial worlds around the Alpha Centauri stars have become more encouraging than ever. Key work in this regard has been performed by Elisa Quintana and collaborators, who have shown in their simulations that, depending on initial disk inclinations, 3-5 such planets might form around Centauri A and 2-5 around Centauri B. We've already discussed that research and I don't want to linger on Quintana's 2002 paper (reference below) other than to note one interesting comparison. When the same initial disk parameters are placed around a single star like the Sun, the accretion of the planetary disk occurs over a much larger expanse of time. Evidently a stellar companion hastens the process of planetary formation, one billion years in the case of the Sun vs. perhaps 200 million years in the Centauri scenario. Quintana, Jack Lissauer (both at NASA Ames) and team went on from that study to look at planet formation around close binaries. And they've now turned to...

Only recently has the idea of habitable planets around red dwarf stars taken hold. But it's a fascinating one, especially if you take a look at the potential window for life to develop on such worlds. M-class red dwarfs live anywhere from 50 billion up to several trillion years, a vast stretch compared with our own Sun's projected ten billion years. And with 75 percent of main sequence stars thought to be red dwarfs, the hunt for life can be expanded enormously if we add red dwarfs to the mix. But getting a stable environment for that life to develop is another matter, for planets in the habitable zone around such stars would be close enough to their primaries to be tidally locked, with one side always in sunlight, the other in darkness. The thought of a frozen dark side and a scalded day side isn't pretty. It wasn't until the late 1990s that models of heat transport within the atmosphere developed that could even out these stark extremes. Now it looks as though habitable worlds...

The news from AU Microscopii couldn't be more interesting, but I'm late getting to it simply because the recent American Astronomical Society meeting left us with so many good things to talk about (wish I could have been there!). But we'll be examining this red dwarf, 33 light years away in the constellation Microscopium (the Microscope) for a long time because it's so useful for study. It's close enough for the Hubble Space Telescope to image it with excellent resolution, and we know from such studies that the star is encircled by a debris disk. Check the image below, where you can see that the disk is nearly edge on as seen from Earth. Image: The dust and debris disk surrounding the star AU Microscopii, as imaged by the Hubble Space Telescope. The lines indicate the polarization of starlight reflected from the disk, which reveals the porosity or fluffiness of the dust grains. The disk is about 120 astronomical units (AU) across, where one AU is equivalent to the distance between...

For some 'hot Jupiters,' at least, changes in the weather aren't much of an issue. In a new study presented at the American Astronomical Society meeting in Seattle, three Jupiter-class planets orbiting within five million miles of their host stars were found to have remarkably similar temperatures globally, even though they're tidally locked. You would expect that a planet with one side turned perpetually toward its star would show considerable temperature variation between the day and night sides, but that does not appear to be the case. "We can't say for sure that we've ruled out significant day-night temperature differences, but it seems unlikely there is a very big contrast based on our measurements and what we know about these systems," said Eric Agol (University of Washington). Agol is lead scientist for the project, which used the Spitzer Space Telescope to measure infrared light from the three systems at eight different positions in their orbits. The study showed no infrared...

With COROT on its way, the search for exoplanets moves into a new phase with an active, space-based transit study. Launched from Baikonur (Kazakhstan) yesterday, the mission's status reports will be available online and should provide fascinating reading. After all, COROT will monitor 120,000 stars with its 30-centimeter telescope, looking for the signatures of planetary transits. That means the kind of 'hot Jupiters' we've already found around many stars, but it should also involve smaller rocky worlds, some perhaps not all that much larger than Earth. But notice what COROT stands for: 'Convection Rotation and Planetary Transits.' The first part of that phrase refers to asteroseismology, the study of stellar interiors by examining the acoustic waves that move across the surface of stars. That means COROT will be able to detect so-called 'starquakes' that well up from deep inside the star. Examining their strength and duration tells astronomers much about the star's mass and...

Take a look at the image of Alpha Centauri in the Centauri Dreams logo. It's the bright object at far left, not the single star that it appears but a triple system whose glare masks its two major components. Centauri A is a G2 star much like our Sun, while Centauri B is a K1. The two are separated by an average of 23 AU, with an orbital period of some eighty years. Indiscernible in the image is Proxima Centauri, an M-class dwarf which is actually the closest star to Earth. Bright, nearby and highly studied, the Centauri stars would seemingly be well characterized. But new results from the European Space Agency's XMM-Newton x-ray satellite show anomalies. Unlike optical wavelengths, where the larger Centauri A dominates, Centauri B is the brighter object in x-ray emissions. What's odd is that repeated monitoring of the two by XMM-Newton shows that Centauri A faded by no less than an order of magnitude in x-rays during the two-year observing range, a behavior out of keeping with all...

If you're thinking about detecting Earth-like planets around other stars, here's an item that may set the pulse racing a bit faster. Michael Endl, who is an expert at the planet hunt around red dwarf stars (he's searched for planets around 100 of them already), notes that the diminutive objects are prime targets for exoplanet hunters. And listen to this: "For the red dwarfs with the lowest masses, like Proxima Centauri, we are sensitive to planets down to two Earth masses using the standard radial velocity technique." Endl works at the University of Texas, out of which a study led by graduate student Jacob Bean has focused on planet formation around red dwarfs -- we looked at this work not long ago. Few gas giants have been detected around red dwarfs. The study examined the dwarfs known to have planets: Gliese 876, Gliese 436, and Gliese 581. Of the three, Gliese 876 is perhaps the most intriguing, as it's known to have two Jupiter mass planets and a likely third, lower-mass world...

You would think Alpha Centauri would be a prime hunting ground for extrasolar planets simply because of its proximity. But the problem for direct imaging is the sheer brightness of Centauri A and B, creating a halo of diffuse light around the pair. Getting through the glare isn't easy, but a search based on twin techniques -- adaptive optics and CCD imaging -- covering a wide-field around the Centauri system has just been completed. Results on the CCD work, using European Southern Observatory equipment, have now been made available and they've come up short on planetary detections. As reported by Pierre Kervella (Observatoire de Paris-Meudon) and Frederic Thévenin (Observatoire de la Côte d'Azur), the team found no co-moving companion objects between 100 and 300 AU. And that's useful information, because it puts some constraints on possible planets around these stars. From the paper: Within the explored area, this negative result sets an upper mass limit of 15-30 M J to the...

The news about possible surface water on today's Mars points out how far we are from characterizing life's possibilities even in our own Solar System, much less around other stars. It may take boots on the ground on Mars to solve the question once and for all, but life in underground aquifers certainly is a plausible proposition, and the sooner we have proof (and samples to study), the better for astrobiology in general. Meanwhile, we push on with the very early wave of exoplanet studies, remembering that it's just over a decade since 51 Peg gave us the first confirmed detection around a main sequence star. I can't imagine a more fruitful field for a young astronomer to head for, with so many possibilities for study that you begin to wonder whether we'll have the human resources to keep up with the vast data inflow that's coming. Some of the more intriguing recent work concerns binaries and the planets around them. If we're getting fairly sanguine about the possibility of planets...

Tau Boötis, a billion year old star some 50 light years from Earth, would be a fascinating place to see up close. The star is orbited by a gas giant some 4.4 times Jupiter's mass, one of those 'hot Jupiters' that close to improbably tight distances with the primary. In this case, the planet/star separation is a mere 0.049 AU, making it about 5 percent of the distance between the Earth and the Sun. 'Hot Jupiters' are bound to be dramatic objects anyway, but this one has other attributes. A team of French astronomers has been able to measure the magnetic field of Tau Boötis itself, finding it just slightly larger than the Sun's. That's the first direct measurement of the magnetic field of a star hosting an exoplanet, and it sets up interesting studies of the interactions between the two bodies as the planet moves so breathtakingly close to its star. Image: An artist's conception of the giant exoplanet orbiting Tau Boötis through the star's magnetic archs. Credit David Aguilar, CfA. In...

We've identified over 200 planets around other stars, but in many ways we know little about other solar systems. The problem is in extrapolating from our knowledge of one or two planets to an entire planetary system, much of which we cannot detect. Can we expect to find gas giants mixed with small terrestrial worlds around most Sun-like stars? And what about the smaller and far fainter red dwarfs? Clearly, the job of characterizing not just planets but entire systems is going to occupy astronomers for many a decade. A new paper from the California & Carnegie team takes helpful steps in that direction. New planet finds are always fascinating, and the team does have four of them, the highlight being the pair orbiting the Sun-like star HIP 14810. Greg Laughlin (UC-SC) writes about that system on the systemic site, noting this: The fact that the orbit is clearly non-circular would be strong evidence for the presence of planet c, even if there weren't enough data to detect c directly. If...

If we're lucky, the COROT mission, to be launched December 21, will be the first to detect rocky planets not much larger than the Earth around other stars. We've looked at COROT recently, and discussed how it and the Kepler space telescope will use transit methods to find these distant worlds. But as you go beyond Kepler (to be launched in 2008), the need for new technologies becomes apparent, which is why planet-finder designs like New Worlds are so significant. Now I see that Claude Catala (Observatoire de Paris-Meudon) is proposing a new take on space-borne telescopes for this purpose. Catala suggests a survey that would gather light from literally hundreds of 10-centimeter telescopes working in tandem (COROT itself is built around a single 27-centimeter telescope). These are small instruments, to be sure, and in some ways less impressive than high-end amateur equipment now on the market. But each boasts a wide field of view, roughly 60 times that of the full Moon. And that helps,...

Watching the population of nearby stars grow is a chastening exercise. It reminds us that even in our own stellar neighborhood, there is much we have to learn. Consider that since the year 2000, the population of known stars within 10 parsecs (roughly 33 light years) of the Sun has grown by 16 percent. That includes 20 new stars identified recently by the Research Consortium on Nearby Stars (RECONS), whose list of the 100 nearest star systems can be found here. As you might have guessed, all twenty of the new objects are red dwarfs, and if you look throughout that 10-parsec volume, 239 of the 348 stars within it (other than our own star) are red dwarfs. That tallies nicely with earlier estimates that red dwarfs make up about 70 percent of the stars in the Milky Way, and points to the obvious fact that when you look up into the night sky, you're getting an unbalanced look at what's around us. None of the new stars are remotely visible with the naked eye. Image: The binary red dwarf...

Jacob Bean, lead author of the paper on red dwarfs discussed here yesterday, weighs in with additional useful information about the study. "The planet-metallicity connection has been firmly established for high-mass (Jupiter and super Jupiter) planets," wrote Bean. "I believe there is not supposed to be a low-mass, including terrestrial, planet formation dependence on disk metallicity (except in the very extreme case of zero metal disks)." The upshot: pre-selecting M dwarfs for possible terrestrial planets still isn't possible based on metallicity, though it may be predictive of gas giant worlds. The expanding dataset on M dwarf metallicity should eventually tell us more.

What kind of stars are most likely to have planets? Narrowing the search is crucial if the goal is to build a target list for space-based missions, especially when we're looking for terrestrial worlds. So learning that planet-bearing stars have higher metal contents -- the elements above hydrogen and helium, presumably as a relic of their protoplanetary disks -- would winnow the target list nicely, at least among Sun-type stars. And most of the extrasolar planets found thus far have been in orbit around stars of the spectral types F, G and K (our Sun is a G-class star). For various reasons, these are the usual targets for radial-velocity surveys, and they're also stars that can be readily analyzed for metallicity. But M dwarfs are the most common stellar type. We need to go to work on their parameters too, especially in the case of dwarfs that have known planetary companions. A stride in that direction is taken by Jacob Bean (University of Texas), Fritz Benedict and Michael Endl...