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...