Although we're beginning to realize that brown dwarfs are widespread in the galaxy, we know surprisingly little about how they form. The question has an obvious impact on planetary formation models as well, but we won't get a good read on the answer until we've been able to study brown dwarfs and other very low-mass stars (VLMS) in multiple systems. Right now, relying largely on the Hubble Space Telescope and direct imaging via adaptive optics, we're unable to detect close binaries in such systems. That leaves radial velocity techniques to do the job. And indeed, a brown dwarf binary designated PPl 15 was found in the Pleiades in the late 90's with these methods. But the hope of landing a large number of close brown dwarf companions has faded. So far, despite ongoing work, we still have only three brown dwarf binaries confirmed through spectroscopy. And we're still asking planet-sized questions: Can a brown dwarf support planets at just a few AU distance? The assumption is yes, given...

Red giant stars have always held a fascination for me, doubtless spurred by an early reading of H.G. Wells' The Time Machine. Who can forget the time traveler's journey far into the future after his desperate escape from the Morlocks, millions of days passing in seconds as he flees: So I travelled, stopping ever and again, in great strides of a thousand years or more, drawn on by the mystery of the earth's fate, watching with a strange fascination the sun grow larger and duller in the westward sky, and the life of the old earth ebb away. At last, more than thirty million years hence, the huge red-hot dome of the sun had come to obscure nearly a tenth part of the darkling heavens. We can forgive Wells the mistaken timing -- thirty million years won't account for this! -- but still revel in the beauty of the concept. How it must have resonated at the end of the 19th Century. Today, red giants seem a bit more familiar as we've learned more about how they happen. And we do know that in...

In a world dominated by short-term thinking, we tend to be driven by media cycles. That makes the coverage of science, among other subjects, problematic. Science operates through the analysis of detail as various minds subject a problem to hypotheses that can be tested experimentally. In other words, good science often takes time, which is why situations like the Gliese 581c story can be so frustrating. Announce a habitable planet around another star and the media love you. Spend months and (if needed) years subjecting the habitability question to analysis and you're not on the public radar. Many scientists have come to question whether Gliese 581c is remotely habitable; some even argue for habitability for the next planet out, Gliese 581d. We're still trying to weigh the data, and such deliberate processes aren't the sort of thing to replace the latest Hollywood starlet scandals on CNN. The good scientist ignores media vagaries and proceeds with the painstaking details. The hunt for...

HD 98800 is an unusual system indeed. About 150 light years away in the constellation TW Hydrae, the four stars that make it up consist of two binary pairs that circle each other. The distance between the two pairs is about 50 AU, which is roughly the average distance between Pluto and the Sun. Imagine having, instead of icy Kuiper Belt objects, a binary star system at the edge of our Solar System. Note: The reference above should probably be to the TW Hydrae association, not 'constellation,' as noted in the comments below. Image: This artist concept depicts the quadruple-star system HD 98800. The system is approximately 10 million years old, and is located 150 light-years away in the constellation TW Hydrae. HD 98800 contains four stars, which are paired off into doublets, or binaries. The stars in the binary pairs orbit around each other, and the two pairs also circle each other like choreographed ballerinas. Credit: NASA/JPL-Caltech/T. Pyle (SSC-Caltech). The idea of planet...

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...

Steinn Sigurðsson (Pennsylvania State) has been reporting from the Greek island of Santorini, where he is attending the Extreme Solar Systems conference. I want to send you at once to Steinn's Dynamics of Cats weblog, where updates are being filed and will presumably continue through today, the conference's last day. It sounds like a terrific gathering filled with the energizing news of discoveries, its theme being, in addition to finding Earth-like planets, the study of exoplanets in tricky places like dense star clusters, near giant stars and orbiting pulsars. That last is fitting enough, given that the first extrasolar planets of Earth-like mass were discovered 15 years ago around the pulsar PSR 1257+12; in fact, the conference meets on the occasion of that anniversary and celebrates as well the sixtieth birthday of Alex Wolszczan, the discoverer of those worlds. All of that and beauteous Santorini too, though as Steinn reports, the heat has been the worst since 1916, as per...

Speaking of bio-signatures, as we did at the end of yesterday's post on planetary atmospheres, take note of the Virtual Planet Laboratory, a working group at the Jet Propulsion Laboratory that is trying to figure out what life's markers might look like across a wide range of biological types. The most obvious signature for life itself is the presence of unusual combinations of things. A world without life shouldn't, for example, give us strong signatures in both methane and oxygen simultaneously. We looked at this subject in an April post, but a recent news release prompts me to put it back into play. The work is highly theoretical, proceeding as it does with no current examples of extrasolar planetary spectra from terrestrial-class worlds to look at. But we can begin with photosynthesis and its variants, as discussed here by Robert Blankenship (Washington University, St. Louis), a member of the group of researchers: "When you consider another world you've got to find that life there...

Where does the Solar System keep its water? Beyond Mars, the trend seems to favor more and more water content the farther out we go. Thus Jupiter, which is considered depleted in water, is eclipsed in these terms by Saturn, though that planet has less water than other volatiles. Move on to Uranus and Neptune and you get into serious water enrichment. "The farther out you go in the solar system, the more water you find," says Bruce Fegley (Washington University, St. Louis). Fegley's work, discussed at the Chicago meeting of the American Chemical Society last March, points to a compelling theory about the outer planets: From Jupiter to Neptune, these are worlds whose atmospheres are 'primary,' drawn directly from the solar nebula as the planets of our Solar System were forming. Just as the Sun is rich in hydrogen and helium, Jupiter likewise shows large amounts of hydrogen and helium, though less carbon, nitrogen and oxygen than the other gas giants. Observations of methane, hydrogen...

Watching the motion of the stars they orbit has been how most of the planets beyond our Sun have thus far been discovered. Such radial-velocity methods are getting more precise all the time, but a likely planet around the nearby star Fomalhaut comes out of an entirely different line of research. Alice Quillen (University of Rochester) is an expert on stellar disks and the planets that help to shape them. And she has learned to predict a planet's size and position from her studies. In the case of Fomalhaut, Quillen worked with Hubble Space Telescope imagery showing the star's surroundings in greater detail than ever before. The Hubble images took advantage of a coronagraph to mask the light of the star to bring out detail in the dimmer ring, confirming what astronomers had previously noted -- Fomalhaut is off-center within its ring. Image: Hubble's view of Fomalhaut's dust ring. Credit: University of Rochester/STScI. Quillen's models examine ring/planet interactions for young stars,...

My younger son Alec can be forgiven a certain amount of confusion over the term 'Planet X.' Back in the 1980s, I told him all about the marvelous Edgar G. Ulmer film The Man from Planet X, a favorite since my own childhood. Ulmer was a gifted director who is rarely talked about today (see his 1945 film Detour for a glimpse of just how gifted). And 1951's The Man from Planet X was compelling in a way that few B movies of the era achieved, with an alien whose spooky presence has stuck with me ever since I first saw him on an old black-and-white set. But then Alec encountered a different 'Planet X' in an astronomy class, learning that some astronomers had searched for a planet beyond Pluto, although at that point with notable lack of success. Planet X was supposed to account for various orbital oddities exhibited by Pluto and become emblematic of a fabulous, unknown place at the very edge of the system that was the ultimate catch for the next Clyde Tombaugh. I didn't think it existed...

Buy a commercial telescope today, equip it with a CCD detector, and you're arming yourself to enter the exoplanet hunt. A CCD, or charge-coupled device, is a sensor that proves far more efficient than photographic film at capturing incoming light. It wasn't so long ago that such tools were available only at large observatories, but no more. Today's amateur can observe a planetary transit, sensing the slight dimming that the planet causes to the starlight as seen from Earth. The trick is knowing when and where to look, and on that score, the Transitsearch network, often working with the American Association of Variable Star Observers, offers ephemeris and transit search results for stars thought to be candidates for such detections. For those new to the term, an ephermeris (pl. ephemerides) is a table plotting the position of celestial bodies. Look to Transitsearch for an example. Greg Laughlin (UC Santa Cruz) noted this morning on the systemic site that he was overhauling the look...

Knowing where to point our future planet-hunter telescopes in space is crucial, because we'll want to maximize observing time for the most likely stellar candidates. There are various ways to narrow the list, but one involves the study of existing spectroscopic data. Charles Lineweaver (Australian National University) calls it a 'poor man's technique,' an inexpensive way to look at the elements within stars and calculate from their abundance the kind of planets that may have formed in that system. The differences between the rocky terrestrial planets in our own Solar System and the outer gas giants are instructive. We can assume that planets form from the same raw materials as the stars they orbit. But the inner planets lack volatile gases like hydrogen and helium compared to the Sun, while maintaining the same abundances of heavier elements like silica and iron. The latter don't vaporise easily in warmer inner orbits. So a star heavy in iron is likely circled by inner planets...