What are the two most fundamental properties of the stars we study? If you said mass and chemical composition, you get the prize, at least as determined by the California & Carnegie Planet Search team. Their new paper lays out the discovery of a gas giant orbiting the M-class red dwarf GJ 317. And they first discuss the discovery in the context of the core accretion model for planetary formation, and the correlation between the metallicity of a star and the chances of its harboring detectable planets. The notion seems sound: The host star inherits its characteristics from the same disk out of which the planets around it form. If you increase the amount of metals in the system (metals being defined as elements higher than hydrogen and helium), you increase the surface density of solid particulates, and that ought to bump up the growth rate for the core materials that become planets. In a gas giant, such a core then becomes massive enough to capture a gas envelope. But the case around...

Astronomers have found a highly elliptical debris disk around the star HD 15115, one that seen virtually edge-on from Earth gives the appearance of a needle running straight through its star. The disk was first imaged by the Hubble Space Telescope in 2006, its unusual shape causing astronomers to request near-infrared imaging by the W.M. Keck Observatory in Hawaii. Keck's images, in conjunction with the Hubble data, revealed the disk's uncommon blue color. So what's going on around this F-class star? First of all, let's distinguish between protoplanetary disks, which give birth to planets, and debris disks like this one, which resemble our own Kuiper Belt. The latter are made up of the remnants of planetary formation. This debris disk seems to extend some ten times further from its star than the Kuiper Belt, according to a Keck news release, though our limited knowledge of the Kuiper Belt makes me a bit wary of the statement, as the latter's dimensions are still under active...

Centauri Dreams sometimes gets e-mail from readers asking how research results can be so contradictory. We've discussed gas giants around red dwarf stars, for example, noting theories that such planets are rare in this environment. And then we come up with stars like Gliese 876 and GJ 317, both red dwarfs, and both sporting not one but two gas giants as companions. But stand by, for in a moment we'll look at new evidence that outer gas giants are indeed rare, and not just around M dwarfs. What's going on? The answer is that exoplanetary studies are a work in progress, and will continue to be as far into the future as I can see. We have identified over 200 exoplanets in a galaxy of several hundred billion stars. You bet we're going to find anomalous situations that challenge every theory we have. And the idea is to put hard scientific work out there for review and critique, noting methodologies and explaining conclusions, thus letting other scientists have a go at the same data. Those...

Probing planetary atmospheres is tricky business at the best of times, but when you're limited to planets you can't even see, the project seems well nigh insurmountable. Nonetheless, astronomers using the Spitzer space telescope are having some success working in the infrared. They focus on transiting hot Jupiters, and earlier this year were able to obtain spectra of exoplanetary light from two such worlds, HD 189733b and HD 209458b. We discussed that work earlier and noted that no water vapor was found in the atmosphere of either planet, despite earlier predictions that it would be. Now a team led by Giovanna Tinetti (Institute d'Astrophysique de Paris) has made further observations of HD 189733b, studying changes in the infrared light from the star as the planet transits, and thus filters the light through its own planetary atmosphere. Working at three different wavelengths, the study showed the clear signature of water. Image: This plot of data from NASA's Spitzer Space Telescope...

Since we've just been looking at stellar metallicity and planet formation, news from the European Southern Observatory catches my attention. A new paper from ESO astronomers discusses the question of planetary debris falling onto the surface of stars, and its effects on what we observe. Evidence has been accumulating that planets tend to be found around stars that are enriched in iron. On average, stars with planets are almost twice as rich in metals as stars with no known planetary system. But what exactly does this result mean? On the one hand, it's possible that stars that are rich in metals naturally enhance planet formation. But the reverse is also possible: It could be that debris from the planetary system could have polluted the star itself, so that the metals we see aren't intrinsic to the star. Bear in mind that a stellar spectrum shows only the star's outer layers, so we can't be sure what's at the core. And in-falling planetary debris would stay in the star's outer...

The Voyager Interstellar Mission sounds like something out of Star Trek, but it is in fact the extended mission of the doughty spacecraft that taught us so much about the outer Solar System. An extended mission can be just as valuable, and sometimes more so, than the original -- think about the continuing adventures of our Mars rovers, working well beyond their projected timelines. In Voyager's case, we're learning much about how the Solar System behaves as it moves through the interstellar medium, and about the heliopause, where the Sun's solar winds effectively lose their dominance over the winds from other stars. Now the Deep Impact spacecraft, which provided such spectacular scenes of Comet Tempel 1, will acquire an extended mission of its own, and in two parts. The one that catches my eye is called Extrasolar Planet Observation and Characterization (EPOCh), which will turn the spacecraft loose on the study of several nearby bright stars already known to have gas giant planets...

The challenge of working with a small sample of exoplanetary systems -- and one tilted toward those detectible through radial-velocity methods -- is that building up solid models of planet formation is tricky. I'm thinking about this in terms of the recent planetary conference at Santorini, and also recalling work performed at the University of Texas, where Michael Endl and team have looked into the relationship between planets around red dwarfs and the metallicity of their stars. It's an intriguing question and one that only continuing observations can nail down. Metallicity refers to the presence of elements higher than hydrogen and helium in a star's composition, something we can determine through spectroscopic analysis. Endl and co-author Fritz Benedict, as originally noted in this post, worked with graduate student Jacob bean on a study of three dwarfs known to have planets: Gliese 876, Gliese 436 and Gliese 581, noting their lower values of metallicity compared to stars of...

In another decade or so, we should have space-based telescopes actively looking for life around other stars by studying the atmospheres of exoplanets. In the beginning, it will make sense to look for bio-chemistries similar to our own. This isn't some kind of species chauvinism but simple realism. We know more about how life works on Earth than it might in far more extreme environments, so we'll turn first to Earth analogues, seeking the bio-signatures of carbon-based metabolisms on worlds with liquid water. But as we explore our own Solar System, the situation will continue to evolve. If life exists on Enceladus, or Ceres, or in some bizarre Kuiper Belt ecosystem, it's not going to be operating on the same principles as life here on Earth. These aren't Earth analogues, and moreover, they are places for which we have the possibility of lander and rover exploration within the forseeable future. We'll want to widen our range so we don't overlook a form of life that isn't immediately...