Those following the Gliese 581 story have been awaiting the results of the MOST observations with great interest. The Canadian mission put the red dwarf under study for six weeks after the recent flurry of speculation regarding a possible habitable planet, Gliese 581 c, in the system. If the planet made a transit, moving across the face of its star as seen from Earth, then we could learn more about its size and makeup. The results are now in, and no transit occurred. But a second issue is a bit more satisfactory. During the observation period, Gliese 581 showed little change in brightness, indicating a level of stability that would prove beneficial to the growth of life, whether on Gliese 581 c or the more distant (and massive) Gl 581 d, which may orbit on the outer edge of the star's habitable zone. Here's Jaymie Matthews (University of British Columbia and a MOST mission scientist) on the matter: "The climate there should not be a wild rollercoaster ride that would make it...

If we're finding planets in places 1500 light years away, as the TrES project just did, why don't we know more about planets in the Alpha Centauri system? One problem is that Centauri A and B are relatively close to each other, with a semimajor axis of 23.4 AU. Leaving Proxima Centauri out of the picture (at 12,000 AU, its short-term effects can be disregarded), it's still true that radial velocity studies have to take the complicated and varying spectra that binaries produce into account. In other words, getting a read on binaries like these in terms of the slight wobbles that signal a planetary presence can consume lots of telescope time. Nonetheless, we do have some data thanks to observations with the Anglo-Australian Telescope. And we've learned this: No planet around either Centauri A or B induces a velocity variation as high as 2 meters per second. The implication is that any planet orbiting either star individually (in what is known as an S-type orbit) has to have a mass less...

Catching up with some older items, I want to be sure to cover a planet recently discovered in the constellation Hercules, because it gives further punch to a fact about exoplanet studies: Off-the-shelf equipment made for amateur astronomers can be effective at detecting new worlds. The planet in question was found by the Trans-Atlantic Exoplanet Survey (TrES) and later observed by the Hungarian Automated Telescope Network (HATNet). Because it blocks out about 2.5 percent of the star's light as it passes in front of it, the transiting TrES-3 readily shows up in these projects' automated surveys. The method is clearly effective. TrES works with wide-field timed exposures, measuring the light from every star in the field to seek out transits. When TrES-3 was discovered with these techniques, it was studied again with one of the 10-meter instruments at the Keck Observatory on Mauna Kea and by the Las Cumbres Observatory in Hawaii, as well as with instruments at Lowell Observatory and the...

Odd planets seem to be sprouting in our data like mushrooms. Take the case of XO-3b. It's got the mass of thirteen Jupiters but orbits its star in less than four days, making it the largest, most massive planet ever found in such a tight orbit. But XO-3b also seizes the attention because its orbit is significantly elliptical rather than circular. Is this evidence for the gravitational effects of another object in the same system? We should be able to learn a lot more about this and other questions because XO-3b is also a transiting world, passing between its star and the Earth. This is the third transiting planet identified by the XO Project, which uses two small telescopes at Haleakala (operated by the University of Hawaii) to identify transit candidates before passing the data on to a network of amateur astronomers for further study. After sufficient evidence is gathered, the work goes back to large telescopes at McDonald Observatory (University of Texas) for confirmation....

What better indication of the success of our planet hunting efforts than the news out of the American Astronomical Society's annual meeting in Honolulu. There, the California & Carnegie Planet Search team announced at least 28 new planets, with four multi-planet systems among them and two borderline cases that need further investigation. That's a bump of 12 percent in the number of known planets over the last year. Behold: With the exoplanet count now not that far from 250, planetary discoveries are coming fast enough that a certain ennui seems to have settled in among press and public. Sure, Gliese 581 c was big news because we thought it was potentially habitable, but finding more and more gas giants probably won't trigger the public imagination, even if GJ 436 b did cause a ripple because of the presence of water. That ripple lasted only long enough for scientists to explain what kind of water they were talking about. Here's Geoff Marcy (UC Berkeley) on the subject: "From the...

New work on Gliese 581's interesting planetary system may prove dismaying for those hoping for a planet in the habitable zone. With two 'super-Earths' and a Neptune class world, this is a system that cries out for close analysis. The Geneva team that detected the super-Earths had calculated surface temperatures on Gliese 581 c at roughly 20 degrees C. What they left out was the likely greenhouse effect of the atmosphere. For habitability -- defined here as the presence of liquid water at the surface -- is not dependent on the central star alone, but also on the properties of the planets circling it. Werner von Bloh (Potsdam Institute for Climate Impact Research) and team tackle the habitability question in terms of atmosphere. From their paper: ...habitability is linked to the photosynthetic activity of the planet, which in turn depends on the planetary atmospheric CO2 concentration, and is thus strongly in?uenced by the planetary dynamics. In principle, this leads to additional...

Brown dwarfs, most of them unobserved, doubtless litter the galaxy. The more we can learn about them and their possible companions, the better for our understanding of how planets form and stars evolve. These minute 'failed stars,' far less massive than the Sun, cannot sustain hydrogen fusion, but they're players in the exoplanet hunt. The brown dwarf 2MASS1207-3932, for example, has a planetary companion of five Jupiter masses, thought to be the first for which an image was obtained. Now we learn that this young star, perhaps eight million years old and surrounded with a protoplanetary disc, is also producing jets of matter. The results, growing out of work at the European Southern Observatory's Very Large Telescope, are surprising. The dwarf's mass is itself only 24 times that of Jupiter, making it the smallest object known to produce such jets. Image: Using ESO's VLT, astronomers found jets coming out from a 24 Jupiter-mass brown dwarf, showing that outflows are rather ubiquituous...

Two gas giants discovered around the star HD 155358 raise again the question of planetary formation and the mechanisms behind it. Most planets detected through radial-velocity methods, which measure the effects unseen companions have on a star's motion, have been found to orbit stars that are high in metal content. 'Metals' in this context means elements higher than hydrogen and helium, and of the two primary models for planetary formation, high metal content seems to favor the one known as the core accretion model, about which more in a moment. What to do about a low metal star whose system is dominated by two massive planets? HD 155358 contains only 20 percent of the metal content of our Sun. Such a finding may favor the rival disk instability model. Here the notion is that the rotating disk of gas and dust in a protoplanetary system becomes unstable not long after it forms, causing it to fragment. As clumps begin to appear, they become large enough to cause their gases to collapse...

One of the most exciting aspects of the exoplanet hunt is that it is not confined to huge telescopes and professional astronomers. Timothy Ferris described the remarkable advances in amateur equipment and observing techniques in Seeing In the Dark (Simon & Schuster, 2002), but he'll need a whole new chapter to cover what's happening not only with distributed computing (as via the systemic collaboration, for example) and the software and hardware advances that let amateurs observe exoplanet transits from sites around the world. Last night Tonny Vanmunster observed the transiting 'hot Neptune' GJ 436 b from his CBA Belgium Observatory in Landen, reporting his results over the Net and this morning on his Web site. Ponder this: GJ 436 b orbits an M-class red dwarf that is 33 light years away. The planet itself has a mass roughly 23 times that of Earth, with a radius approximately that of Neptune. There was a time when Neptune itself would have been a tricky catch for the average amateur,...

Whether or not Gliese 581 c, that intriguing world that may or may not offer temperatures conducive to life, will make a transit of its star is not yet known. But the principle that radial-velocity searches can identify a planet that is subsequently studied via transit received further validation today with the detected transit of a Neptune-class world around GJ 436. This is the smallest and least massive planet ever examined through transit methods, and it bodes well for future such studies of M-class stars. The new transit comes courtesy of the Swiss team that includes Michel Mayor and Didier Queloz, recently in the news due to their work on Gliese 581 c -- do these guys ever get any sleep? As Andy noted in a comment this morning, this 'hot Neptune' orbits closer to its star than the innermost planet of Gliese 581. GJ 436 is an M-class red dwarf, a type of star whose small radius makes the detection of such worlds by transit methods easier than would be the case for solar-type...

We'd all like to know more about Gliese 581 c, the most talked about exoplanet of them all because of the possibility -- however controversial -- that it may be habitable. One way to learn more would be to observe a transit, which is what the Canadian space telescope called MOST is now attempting to do. The odds are roughly one in thirty, according to MOST principal investigator Jaymie Mark Matthews, but even the few observations ahead for MOST will tell us more about the star in question. Matthews' thoughts are reported in an article in the British Columbian alternative daily The Tyee, along with a nice backgrounder on the planet by writer Monte Paulsen. Evidently the Swiss team behind the Gliese 581 c announcement, which includes Michel Mayor and Didier Queloz (the first to identify an exoplanet, in 1995), had contacted the MOST controllers at the University of British Columbia before going public with their latest work. They hoped a transit could verify the existence of the new...

40 Eridani is a triple-star system some 16 light years from Earth. If it rings a faint bell, that's probably because of its association with Star Trek. In the universe of the show, 40 Eridani is home to Vulcan, birthplace of the inscrutable Mr. Spock (Gene Roddenberry himself signed off on the idea). Not so long ago, the existence of planets would have been doubted in such a system, but we're learning that double and even triple star systems can and do support planets. So maybe there is a 'Vulcan' out there after all, though doubtless sans humanoids with pointy ears. In any case, the elements of this system are widely spaced, and 40 Eridani A is a K-class star not so different from Centauri B, a star that could well support Earth-mass planets. Recently Angelle Tanner (Caltech) embarked on simulations designed to show whether or not the Space Interferometery Mission (known as SIM PlanetQuest) might be able to detect such a world. Tanner's work confirmed that a planet like this in the...

Impressive results released today show just how much we're learning about the 'hot Jupiters' that comprise about a quarter of known exoplanets. The first concern HD 149026b, a distant world which the infrared Spitzer instrument has shown to be the hottest planet ever studied. It's somewhat smaller than Saturn but more massive, and is thought to contain more heavy elements than could be found in our entire Solar System outside the Sun itself, with a core as much as 90 times the mass of the Earth. And the odd thing about HD 149026b is that for it to reach the measured temperature -- a smoking 3,700 degrees Fahrenheit, or 2,300 degrees Kelvin -- it would have to be absorbing just about all the starlight reaching it. The upshot is a planet whose surface is blacker than charcoal, re-radiating incoming energy in the infrared. What a view for the nearby traveler: "The high heat would make the planet glow slightly, so it would look like an ember in space, absorbing all incoming light but...

The early news from COROT couldn't be more encouraging. Just sixty days into its science mission, the spacecraft has found its first transiting exoplanet and has returned information about the interior of a star. The latter findings point to COROT's role in asteroseismology, the study of stellar interiors through analysis of the star's light curves. What has mission scientists smiling is that in both cases, the instruments they're watching show signs of working even better than planned. True, the data carrying these results are still noisy and in need of plenty of analysis, but COROT project scientist Malcolm Fridlund sounds quite an optimistic note: "The data we are presenting today is still raw but exceptional. It shows that the on-board systems are working better than expected in some cases - up to ten times the expectation before launch. This will have an enormous impact on the results of the mission." One would think so. It raises the stakes for COROT from detecting...

Last night I was thinking that the day would come when all the planets we've been discovering have proper names instead of stark designations in catalogs. Then I realized that this is unlikely. As the rate of planetary discoveries accelerates through space-borne missions and ever more precise detection methods here on Earth, it may be that we'll keep generating new finds faster than the naming process can catch up with them. So I guess we should get used to designations like Gliese 581 c. Of course, a planet can have multiple designations, depending on how it's catalogued or found. The recently announced gas giant HAT-P-2b (a very strange place indeed) is called this not for its place in a catalog but its discovery method, the HAT network of automated telescopes. HAT stands for Hungarian-made Automated Telescope, but the project is headquartered at the Harvard-Smithsonian Center for Astrophysics (CfA) and works with instruments in Arizona, Hawaii and in this case, Israel. Its focus:...

We need to know more about how stars age. Ponder this: Centauri A and B are perhaps 2.5 billion years older than our Sun. If we're interested in the development of intelligent life, older is clearly better -- who knows what Earth might develop in the next two billion years? But are there planets around either of the primary Centauri stars? And if there are, how have their planetary systems changed over the course of those milennia? Addendum: See the comments below -- my figure of 2.5 billion years older than the Sun is in the middle of more extreme age estimates in both directions, and even these are questioned by the work we discuss in the following paragraphs. One way to study these things is by looking at how stars rotate. A recently announced method called gyrochronology works with the premise that a star's age is tightly bound up with both its rotation and its color. Syndey Barnes, who developed the technique at Lowell Observatory, explains it this way: "If you know the...

We'd all like Gliese 581 c to be as Earth-like as possible, but not everyone puts high odds on the planet being even potentially habitable. In an e-mail discussion circulating among space professionals, Gerald Nordley took issue with the 'terrestrial world' concept and pointed out how the results of Stephane Udry and the Geneva exoplanet team shouldn't be taken too far. Nordley, a retired Air Force astronautical engineer, is a familiar name to those who follow interstellar studies from his work in the Journal of the British Interplanetary Society as well as his essays in venues like Analog. He is also the author of numerous science fiction stories. Here are Nordley's comments, reprinted with permission: Udry et al., make a good case for a planet being there, but the rest looks speculative at best. The planet has a minimum mass of 5 Earths, the "1.5 Earth radius" is based on a density assumption with no data behind it, and the planet's insolation is about 2.44 times the Earth's (L/a2...

Just what might we find on Gliese 581 c, the potentially habitable planet announced yesterday? Much depends on where the planet formed in its circumstellar system. For that kind of information I listen to Greg Laughlin (University of California at Santa Cruz), whose work on planetary formation via core accretion seems to gain stature with every new planetary find. Here's Laughlin's take from his systemic weblog: The planet probably migrated inward to its current location from beyond the “snowline” in GL 581’s protostellar disk, and so its composition likely includes a deep ocean, probably containing more than an Earth’s mass worth of water. Atmospheric water vapor is an excellent greenhouse gas, so the conditions at the planet’s atmosphere-ocean boundary are probably pretty steamy. It’s also possible, however, that the planet formed more or less in-situ. If this is the case, it would be made from iron and silicates and would be fairly dry. It’s unlikely, but not outside the realm of...

This is a big one, and it happens several years earlier than I had expected. A planet of about five times Earth mass, one whose radius is only 1.5 times that of our own world. Moreover, a planet that's smack in the middle of its star's habitable zone, with a mean temperature estimated at between 0 and 40 degrees Celsius. The models in question say that this is a rocky world, and its temperatures tell us that oceans could exist there. The first detection of a planet where carbon-based life could conceivably exist makes this one a find for the history books. The star is Gliese 581, already known to be home to a planet of Neptune mass and a possible third world about eight times as massive as Earth. It's an M-class red dwarf, far smaller and cooler than the Sun. The new planet, the smallest found up to this point, orbits it in 13 days. Gliese 581, it should be noted, is comparatively close to our own Solar System, about 20.5 light years away in the constellation Libra. Radial velocity...

Investigating brown dwarfs is not for the faint of heart. With a mass below what's needed to sustain hydrogen-burning fusion, they're hard to see, and they may be far more numerous than we've previously estimated. Nor do we have a good handle on how they function, to judge by a new study showing that these objects can possess powerful magnetic fields. It turns out that the 'failed star' designation may be a bit inapt. Sure, they're dim objects but in recent years, it has been discovered that some brown dwarfs put out beams of radio waves that are thousands of times brighter than any detected from our Sun. Brown dwarfs, in other words, are actually pretty lively. If you think about other sources of flashing radio signals, pulsars come immediately to mind. Their powerful magnetic fields and incredibly fast rates of rotation make figuring out how they produce their signals a difficult matter. Now we find brown dwarfs emerging as a second class of stellar objects that produce such...