Serendipity is a wondrous thing. Start writing about the early history of the Solar System, as I intended to do yesterday, and you wind up discussing 'hot Jupiters' around other stars. But there actually is a bridge between the two concepts, and it comes in the form of a question. If we find gas giants in scorchingly hot orbits around other stars, why was there no hot Jupiter in our own Solar System? Or was there? That question was what originally led me to the paper by Avi Mandell, Sean Raymond and Stein Sigurðsson that occupied yesterday's post. For in their analysis of how giant planets migrate through an early planetary system, wreaking havoc on newly forming worlds but also scattering them interestingly throughout nearby space, these researchers paused to examine the implications of these studies for our own system. Having demonstrated through their simulations that the migration of a gas giant through an inner system may be common, and that systems that experience it often form...

What happens to potentially habitable planets when a gas giant swings through the neighborhood? It's a pertinent question when you consider the surprises that 'hot Jupiters' have given us. 22 percent of known extrasolar planets show an orbital radius of less than 0.1 AU, and 16 percent are located within 0.05 AU of their host star. That's a surprise given the assumption that these gas giant planets must form much further out in their systems, but it can be explained by inward migration of the giant planet, a process under much study that is generally thought to be caused by interactions with the protoplanetary disk. Such a migration would seem to spell trouble for planets already orbiting closer to the star, leading some to believe that systems with hot Jupiters are unlikely homes for living worlds. But recent simulations of the growth of such systems make it clear that a hot Jupiter isn't necessarily a deal-breaker for habitable worlds. Are we going to have to add such systems into...

56 light years from Earth, the star Iota Horologii is a member of the 'Hyades stream,' a number of stars moving in a similar direction with respect to the rest of the galaxy. It's also an exoplanet host star, known to have a planet twice the mass of Jupiter in a 320-day orbit. The two factors -- the position of the star within the stream and the planet that accompanies it -- play into an unusual application of asteroseismology, the study of the sound waves that move through a star. I want to note this work particularly because it has a bearing on planet formation, about which the more we learn the better as we continue the hunt for exoplanets. But let's pause on asteroseismology itself. You may recall that using this technique for studying the interiors of stars is one of the purposes of the COROT mission, the other being the detection of planetary transits. Asteroseismology is invariably explained with musical metaphors, likening the sound moving within a star to the ringing of a...

Although the image below isn't particularly striking, do focus in on it for a moment. You're looking at what astronomers now consider the coldest brown dwarf yet to be found. Look just down from the top of the image and just left of center for the unusually red pinpoint. This is CFBDS J005910.83-011401.3, thankfully abbreviated CFBDS0059. A science fiction writer with brown dwarf credentials (Karl Schroeder is just the guy) could think of a more poetic name and set up a story around such a place. Image: Three-color image of the star field in which the brown dwarf has been discovered. The brown dwarf is the very red object seen at the top left of the image. This image illustrates how very different is the color of this object compared to the other cold stars around. Image copyright Canada-France-Brown-Dwarf-Survey 2008. As interesting stars go, CFBDS0059 isn't all that far away, some forty light years. Massing between 15-30 Jupiter masses, it's typical of brown dwarfs in at least one...

Keep your eye on a project in the Canary Islands called the New Earths Facility. Using a laser measuring device now being tuned up for the job, scientists intend to continue the hunt for terrestrial worlds with a greater than ever chance of success. Called an astro-comb, the device brings far greater precision to our existing Doppler techniques for finding exoplanets. In fact, early reports suggest it may increase the resolution of these methods by as much as one hundred times, making the detection of an Earth-like world in an orbit similar to ours feasible. Now we're getting into interesting territory indeed, not only in terms of planetary detections themselves but synergies with the ambitious Kepler mission, to be launched in 2009. Read on. Studying the Doppler shift of distant starlight has already achieved a remarkable precision, capable of finding planets down to about five Earth masses in orbits as far from the star as Mercury. But the farther we get from the star, the trickier...

Long before the first exoplanets were found, one speculation about our own Solar System was that a passing star had disrupted the solar nebula so as to promote the formation of planets. We now know that planets form in many ways, but it's interesting to see that HL Tau, a star discussed yesterday at the Royal Astronomical Society meeting in Belfast, may have been influenced by a recent close pass by XZ Tau, another young star nearby. Did this 'flyby' disrupt the circumstellar disk around HL Tau, helping to form a proto-planet that has now been observed? Whatever the case, we do seem to have interesting processes at work around HL Tau. The newly discovered proto-planet is thought to be only one percent of the age of a planet found last year around TW Hydrae, a world ten times the mass of Jupiter that was once the youngest planet yet detected. That one orbited inside the inner hole of a pronounced circumstellar disk. HL Tau b remains little more than a bright clump within its dusty...

Results from the Wide Angle Search for Planets (SuperWASP) could hardly be better. In the last six months, astronomers using wide-field cameras in the Canary Islands and South Africa, working in conjunction with a battery of telescopes around the world, have identified ten new planets around other stars. The findings were announced yesterday at the Royal Astronomical Society's national meeting in Belfast. We're dealing with planetary transits here, planets moving across the face of their star as seen from Earth. 46 transiting worlds are known, of which SuperWASP has now found a solid fifteen. Skymaps, coordinates and background information on all the SuperWASP planets can be found here. You'll want to concentrate on WASP-6b through 15-b for the new ones, which include 'hot Jupiters' like WASP-12b (orbiting its primary, a G-class star 870 light years from Earth, in just over a day) and WASP-15b, one-half the mass of Jupiter, orbiting an F5 star a thousand light years away. The largest...

Budding astrobiologists should be thinking about the significance of red dwarf stars as they approach their careers. Let's say, as pure speculation, that one out of every thousand stars in class M has a planet in the habitable zone. That works out to 75 million potentially habitable planets around these stars in our galaxy alone. Note the assumptions I'm making. First, I peg M dwarfs at 75 percent of the galactic population. That figure is widely in use and I've just run across it again in a new paper by Paul Shankland (US Naval Observatory), David Blank (James Cook University, Australia) and colleagues, about which more in a moment. Another assumption: That the Milky Way holds about one hundred billion stars. That's low-balling the number, I think, because estimates seem to start at that figure and go up to four or five times as high. So my 75 million potentially habitable planets, while just a guess, may not be totally off the wall. Image: An artist's impression of a gas giant...

I've never met George Ricker, but in at least one respect I believe he thinks the way I do. Ricker is senior research scientist at MIT's Kavli Institute for Astrophysics and Space Research, and he's someone who can connect the exoplanetary systems we study with places we might eventually go. As witness this comment in a discussion of a planned satellite-based observatory being designed at the Institute: "Decades, or even centuries after the TESS survey is completed, the new planetary systems it discovers will continue to be studied because they are both nearby and bright. In fact, when starships transporting colonists first depart the solar system, they may well be headed toward a TESS-discovered planet as their new home." It's wonderful to see a 'when' rather than an 'if' when referring to starships, even though everyone concerned can appreciate the blue-sky nature of the comment. For my part, I'll take whatever the physics will bear, from close-up imagery of terrestrial exoplanets...

The recent news that there may be an underground ocean on Titan tantalizes us in astrobiological terms. It also brings us up against the question of how to define a habitable zone. The standard definition involves the presence of liquid water at the surface, a reasonable requirement when you're looking for carbon-based life. But it's also true that exobiology may one day be studying forms of life that are nothing like us, living in environments we would at first dismiss from our list of living places. Just how far does a habitable zone extend? First, a short defense of the status quo. As we expand our exoplanet hunt and become capable of detecting the signature of life on distant planets, we need a target list to optimize our search time. It's entirely reasonable to fine-tune that list toward conditions similar to what we find on Earth because the life on our planet is the only kind we've been able to study. Detecting its biomarkers in an alien atmosphere is a sensible goal. We know...

Well-studied HD 189733b is a Jupiter-sized planet again in the news. Studying this transiting world, scientists using Hubble Space Telescope data have made the first identification of an organic molecule -- methane -- in the atmosphere of an exoplanet. What's particularly significant here is the growing sophistication of our use of spectroscopy, splitting light into its components to tease out the constituents of the atmosphere under study. This new finding shows that we're on target in planning to use space-based observatories to make far more challenging detections. Image: A wide field image of the region of sky in which HD 189733b is located. In this image we can see the asterism of the "Summer Triangle" a giant triangle in the sky composed of the three bright stars Vega (top left), Altair (lower middle) and Deneb (far left). HD 189733b is orbiting a star very close to the centre of the triangle. Credit: A. Fujii. Methane in the atmosphere of a gas giant wouldn't rank as a...

We have interesting news coming up this week with regard to the first detection of methane in the atmosphere of an exoplanet, of significance because it demonstrates that we can detect organic molecules using spectroscopy in ways that will one day help us study the atmospheres of terrestrial worlds around other stars. More on this later in the week, after a NASA teleconference scheduled for the 19th. Today, though, let's talk about another kind of detection in the circumstellar disk of a young star. At work in the latter is the Spitzer Space Telescope's infrared spectrograph, which is being put to use to look at the composition of protoplanetary disks. Specifically, John Carr (Naval Research Laboratory) and Joan Najita (National Optical Astronomy Observatory, Tucson) have been examining gases in the planet forming region around the star AA Tauri, using refined methods that have allowed them to find the spectral signatures of three organic molecules: Hydrogen cyanide, acetylene and...

Keep your eye on Gliese 581. Not that the news is necessarily good for our hopes for habitability around that star -- in fact, a recent paper suggests quite the opposite. The red dwarf exploded into the public consciousness with the announcement that one of its planets -- Gl 581 c -- could conceivably support clement temperatures and water at the surface, at least in places. But in exploring that possibility, we're getting a case study of world-class science at work, analyzing data, offering hypotheses, broadening options. It's an exciting process to watch. Gl 581 d is now being analyzed for habitability, while Gl 581 c begins to appear less and less likely as a home to life. It may take decades and new space-based observatories for the issue to be resolved, but we now have a new take on Gl 581 c, embedded in a broader study of tidal evolution as planetary systems evolve. The study has implications not just for rocky worlds but for planetary formation in many scenarios. The work of...

A new observing program designed to study planets around small, cool stars is in the works. TEDI, the TripleSpec - Exoplanet Discovery Instrument, saw first light on the 200-inch Hale Telescope just before Christmas, and is now in its commissioning phase, with an observing program scheduled to begin this spring. And for those who occasionally wonder why we seldom discuss stars like Barnard's Star or Proxima Centauri in terms of the planet hunt, read on. For TEDI is the kind of program that should be able to survey not just M dwarfs but L and T class stars as well, opening exciting possibilities for discovery. Planets around Proxima Centauri? Perhaps, and extending all the way down to T-class brown dwarfs makes things interesting as well. But finding such planets is a challenge with conventional radial velocity methods. Here's why: Radial velocity searches are generally conducted in the optical band, and work well with stars, like the Sun, that are bright at these wavelengths. The...

In today's world, one of the more useful gifts for a scientist to have is the ability to save money. Enter the Jet Propulsion Laboratory's Wesley Traub, who copes with problems like NASA's indefinite hold on Terrestrial Planet Finder with a low-cost alternative of his own. Last year, Traub and crew experimented with the Solar Bolometric Imager, an observatory lofted by a balloon to altitudes of 35 kilometers and more. Their study of air distortions at those altitudes convinced Traub that the balloon's movements through the stratosphere would not distort received images, and that led to speculation about doing exoplanet science close to home. A balloon-based TPF? Hardly, but Traub does talk about imaging perhaps twenty exoplanets, according to a recent story in New Scientist. The method: A coronagraph teamed with a one to two-meter mirror. The so-called Planetscope weighs in at $10 million, making it a bargain when compared to space-based observatories, and cheap enough to tempt...

What are the chances that we'll find habitable planets around Alpha Centauri A and B? Centauri Dreams has long kept an eye on the work of Greg Laughlin (UC-Santa Cruz) and colleagues, who have been working on the Alpha Centauri question with ever more interesting results. Following their work on Greg's systemic site has been fascinating, and for those who would like to be quickly brought up to speed, it's useful to know that Laughlin has made their recent paper summarizing these findings available online. Anyone serious about the study of these closest stars to Earth will want to download and read these promising results. Laughlin's group simulated the formation of planetary systems around Centauri B, beginning with a disk populated with 400 to 900 lunar-mass protoplanets, then following its development over 200 million years. To say the results are encouraging would be an understatement. All the simulations lead to multiple-planet systems, with at least one planet of Earth mass or...

Centauri Dreams has long championed Webster Cash's innovative New Worlds mission concepts, which would use a 'starshade' to block the light of distant stars to reveal their planetary systems. Cash envisions using multiple spacecraft for this assignment, one the starshade itself, the other a telescope that would make the needed observations. After a series of ups and downs, New Worlds now receives new life in the form of a $1 million award from NASA to study the starshade's possibilities. Remember that we're still at an early research level when it comes to funding of this kind -- the actual observatory, a design Cash calls New Worlds Observer -- would cost an estimated $3.3 billion to design and build. Other mission concepts are still in play (fully nineteen observatory concepts have been chosen for further study), so the road ahead is by no means clear as we look toward space missions that can identify Earth-like planets around other stars. But Cash's designs are well vetted, and...

What exactly is that dark material spread so widely over Saturn's various moons? From Hyperion to Iapetus, Dione and Phoebe, we find a black substance coating a wide range of objects, suggesting that whatever the stuff may be, there must be a common mechanism for moving it from one moon to another. A series of papers on Saturn's moons appears in the February issue of Icarus, where these interactions are now under study. Just what the material is remains a mystery. But Roger Clark (US Geological Survey) notes that as the Cassini data build, we're beginning to track down some of its components, including bound water and, possibly, ammonia. Studying Dione, Clark's team noted the fine-grained nature of the dark material there. Its distribution and composition indicate the dark material is not native to the moon, and indeed, the same signature appears not only among other moons but also in Saturn's F-ring. From the abstract to the study by Clarke and colleagues: Multiple lines of evidence...

About two weeks ago we looked at the work of Michael Meyer (University of Arizona), whose team examined over 300 Sun-like stars (spectral types F5-K3) at mid-range infrared wavelengths. A wavelength of 24 microns detects warm dust, material at temperatures likely to be found between 1 and 5 AU from the parent star. The headline that day was Meyer's contention that many if not most such stars produce terrestrial planets. Now Meyer is presenting these findings at the annual meeting of the American Association for the Advancement of Science, doubtless putting the exoplanet hunt back in the daily papers, at least for a day. Bear in mind that in using the term 'terrestrial' we're talking about small, rocky worlds like the inner planets of our Solar System. That could include worlds like our own, of course, but could also include hellish places like Mercury and Venus and their analogues around other stars. Nonetheless, it's exciting to think that the chances of rocky planet formation are...

Finding solar system analogs is tricky business, as we saw yesterday when examining the discovery of Jupiter and Saturn-class worlds around a distant star. That find, I notice, is getting some attention in the popular media as an indication that our Solar System may not be unique. But take a look at the gas giant recently found around HD 154345 if you want to see an even closer analog to our own system. HD 154345b is a single world, to be sure, but it orbits a G8 dwarf much more like the Sun than the diminutive star examined yesterday, and it's a close match for Jupiter not only in size but orbital position. The planet's minimum mass is 0.95 Jupiter's, and its 9.2 year circular orbit carries it around its star at a distance of some 4.2 AU. Sound familiar? What's happening around HD 154345 is more or less what a distant astronomer using our current technologies would see if observing our Solar System. Rather than using microlensing, the discovery team here put radial velocity...