While we're this early in the game of detecting life signs from distant planets, it makes sense to focus on surface habitability, which is why oceans are so interesting. Sure, we can imagine potential biospheres under the ice of a Europa or even an Enceladus, but given the state of our instrumentation and the distance of our target, going after the most likely catch makes sense, and that means looking for oceans. Significant work from the EPOXI mission has given us some of the parameters for studying a planet like ours using multi-wavelength photometry. EPOXI, you'll recall, is the extended mission of the Deep Impact spacecraft that drove an impactor into Comet Tempel 1 in 2005 and is now enroute to Comet Hartley 2. Its views of Earth are being used to help scientists prepare for studies of terrestrial worlds around other stars. Planets with large bodies of water should reflect light from their star differently than dry planets, and as the observed planet goes through its phases as...

Globular clusters held an early fascination for me, and I guess anyone who encounters these rich cities of stars for the first time wonders what it would be like to be on a planet deep inside one of them. The clusters appear to be distributed in a spherical halo around the galactic center, ancient collections of stars much lower in heavy elements than stars in the galactic disk (although globular clusters in some other Local Group galaxies seem younger). The thought of the night sky on a planet embedded in such a place makes the mind reel, star upon star upon star filling the view. Image: The globular cluster 47 Tucanae, the second brightest globular cluster orbiting the Milky Way (behind Omega Centauri). Imagine the night sky deep within such a cluster. Credit: South African Astronomical Observatory. But a new paper suggests that at least one category of planets may be rare in such clusters. It follows up on an earlier survey of the cluster 47 Tucanae which examined some 34,000...

The ExoClimes 2010 conference ("Exploring the Diversity of Planetary Atmospheres") is well in progress in Exeter (UK) as I write, with its talks now being posted online and the hope that video of the presentations will soon be available on the conference site. Already the latest lingo is in the air, as in 'Hermean,' a term used by Brian Jackson (NASA GSFC) to describe hot, rocky exoplanets with tenuous atmospheres. The analogy is with Mercury, though these are even hotter places with magma oceans and melted surfaces, leading to what Jackson calls a 'rock vapor atmosphere' that just might be visible given sufficient spectral resolution. But what catches my eye this morning, as I survey the ongoing conference buzz online from an ocean away, is Franck Selsis (Laboratoire d'Astophysique de Bordeaux) and his work on the atmospheres of short-period terrestrial exoplanets. Selsis is interested in the habitability of planets around M-dwarfs, noting their strong tidal interactions with their...

We're entering the era of the 'super-Earths,' when rocky planets larger than our own will pepper the lists of new discoveries. These smaller worlds will occasionally make a transit of their star, as does CoRoT-7b, and that's when things really get interesting. After all, we know that secondary eclipses, in which a transiting exoplanet swings behind its star as seen from Earth, can be used to study distant atmospheres. The method collects light from both star and planet and, when the planet is hidden, subtracts the starlight to get the planetary signature. Now Lisa Kaltenegger (Harvard-Smithsonian Center for Astrophysics) and colleagues Wade Henning and Dimitar Sasselov are advancing the idea that we can use near-term instrumentation like the James Webb Space Telescope to spot volcanic eruptions using these same methods. Their model is based on eruptions on an Earth-like planet, extrapolating from what happens on our world to suggest that sulfur dioxide from a major volcanic event on...

Somewhere around 2000 light years away in the direction of the constellation Lyra is a Sun-like star orbited by at least two Saturn-class planets. What's interesting about this news, as just discussed in the Kepler press conference I've been listening to this afternoon, is that for the first time we've detected and confirmed more than one planet around a single star using the transit method. But much more important, transit timing variations -- the leads and lags of the two planets as they transit the star as seen from Kepler -- can be used to tease out new and significant information. Kepler-9b and 9c mark the first clear detection of transit timing variations by Kepler, allowing us to study the gravitational interactions between the planets involved. And that's useful stuff: We see two planets in a 2:1 orbital resonance, one with a 19.2-day orbit, the other with a 38.9-day orbit. As the inner planet completes two orbits, the outer planet completes one. The variations in transit...

In a sense the planets discovered around the Sun-like star HD 10180 are no surprise. We’ve long assumed that planetary systems with numerous planets were common. We lacked the evidence, it’s true, but that could be put down to the limitations of the commonly used radial velocity method, which favors massive worlds close to their stars. But we’re getting much better at radial velocity work and, using instruments like the HARPS spectrograph at the European Southern Observatory’s La Silla (Chile) telescope, we’re teasing out ever more exquisite signals from distant systems. More and more multiple-planet scenarios are in our future. Noting that high-precision radial velocity surveys are now able to detect planets down to roughly 1.9 Earth masses, the paper on the HD 10180 work frames the situation this way: Preliminary results from the HARPS survey are hinting at a large population of Neptune-like objects and super-Earths within ?0.5 AU of solar-type stars (Lovis et al. 2009). Moreover,...

The image of double suns rising over the planet Tatooine from the first Star Wars movie never quite goes away. I remember watching the film in a theater about a week after its release, being dazzled by the visuals but thinking that a planet in an orbit around both stars of a binary would have to be well outside the habitable zone. I didn't believe in Tatooine, in other words, though now I'm a bit more circumspect. A couple of years ago Cheongho Han (Chungbuk National University, Korea) wrote a paper suggesting that microlensing might be of use in finding a planet fitting this description, if indeed such a planet exists. Then yesterday Massimo Marengo dropped me a note about new work he has been involved in that puts a damper on the idea of terrestrial worlds in such settings. Long-time Centauri Dreams readers will remember Marengo, whose fascinating work on Epsilon Eridani we've covered in these pages on several previous occasions. Now at Iowa State University, the astrophysicist has...

Planetary systems around dim brown dwarfs are a fascinating thing to contemplate, and for a vivid imagining of future human activities on such planets, I'll send you to Karl Schroeder's Permanence. The 2002 novel posits ingenious engineering to sustain bases on such worlds, and even comes up with an interstellar propulsion method powered up by their energies that sustains an expanding starfaring culture. A brief sample of Schroeder's universe (not enough to be a spoiler): ...the brown dwarfs each had their retinue of planets -- the halo worlds, as they came to be called. And though they were not lit to the human eye, many of these planets were bathed in hot infrared radiation. Many were stretched and heated by tidal effects, like Io, a moon of Jupiter and the hottest place in the Solar System. And while Jupiter's magnetic field was already strong enough to heat its moons through electrical induction, the magnetic field of a brown dwarf fifty times Jupiter's mass radiated unimaginable...

We're learning a lot more about how planets interact with each other gravitationally. 'Resonance' is the operative term here. When planets are locked in a 2:1 orbital resonance, the outer planet orbits the host star once for every two orbits of the inner planet. A 3:2 resonance occurs when the outer planet orbits the star twice for every three orbits of the inner planet. Resonance (technically 'mean motion resonance') prevents close encounters between planets and provides long-term orbital stability. And if the 2:1 resonance is the most common pattern, it's also true that things can change when planets migrate to different parts of their system. John Johnson (Caltech) describes the result of fast inner migration: "Planets tend to get stuck in the 2:1. It's like a really big pothole. But if a planet is moving very fast it can pass over a 2:1. As it moves in closer, the next step is a 5:3, then a 3:2, and then a 4:3." Johnson's work on resonance has born fruit in a new paper in which...

Dimitar Sasselov, a co-investigator on the Kepler mission, said in a TED Talk just posted that Kepler had uncovered numerous terrestrial planet candidates in its early data. Have a look at the video below (around the 8-minute mark). "Small planets dominate the picture," says Sasselov, showing a chart of planet candidates. A great deal of work has to go into confirming these results, but Sasselov goes on to say "The statistical result is loud and clear, and the statistical result is that planets like our own Earth are out there. Our Milky Way galaxy is rich in these kinds of planets." How many will be confirmed, and how many shown to be habitable? Much work ahead.

The exoplanet HD 209458b is the subject of such intense scrutiny that the discovery of a comet-like 'tail' is almost anti-climactic. After all, this transiting 'hot Jupiter' has given us plentiful information about its atmosphere (including the presence of a massive storm), and its tight orbit around its primary, orbiting that star in 3.5 days, would imply an atmosphere in continual turmoil. Now we learn that some of the atmosphere is indeed escaping into space, with the result that stellar winds evidently push the cast-off material into a long stream behind the planet. Jeffrey Linsky (University of Colorado in Boulder) explains the observations: "Since 2003 scientists have theorized the lost mass is being pushed back into a tail, and they have even calculated what it looks like. We think we have the best observational evidence to support that theory. We have measured gas coming off the planet at specific speeds, some coming toward Earth. The most likely interpretation is that we...

Learning about planets through inference is a necessary procedure, given the state of our technology. We do have a few direct images of exoplanets now, but when relying on radial velocity data or transits, we're looking at the effects planets cause upon our measurements of their stars. With CoRoT and Kepler now yielding high-quality transit data, it's encouraging to see how we can go to work on this information to learn even more about the systems they study. Thus the announcement of WASP-3c, a second planet found around a star in the constellation Lyra, whose existence was pegged by its effect on the previously known planet. WASP-3b was discovered by the Wide Angle Search for Planets project (SuperWASP), a British extrasolar planet detection program that uses robotic observatories that monitor stars for transit events. Eight wide-angle cameras monitor millions of stars, with 26 exoplanets now discovered. The new work, led by Gracjan Maciejewski (Jena University, Germany) went to...

Exoplanet hunting takes time, a fact that is well demonstrated in the case of a newly confirmed gas giant. Eight times as massive as Jupiter, it orbits a star much like the Sun but at a distance vast enough (300 AU) to place it well within the Kuiper Belt if it were in our own system. 1RXS 1609 b was first reported back in September of 2008 when David Lafrenière (now at the University of Montreal) and team used adaptive optics to take direct images and spectra of the object, which can be seen in the image below. Image: First released in September of 2008: Gemini adaptive optics image of 1RXS J160929.1-210524 and its ~8 Jupiter-mass companion (within red circle). This image is a composite of J-, H- and K-band near-infrared images. All images obtained with the Gemini Altair adaptive optics system and the Near-Infrared Imager (NIRI) on the Gemini North telescope. Credit: Gemini Observatory. This was thought to have been the first planet directly imaged around a Sun-like star, but...

Combining the assets of multiple telescopes in the technique known as interferometry has a long pedigree. Using a cluster of small telescopes rather than a single gigantic one is a way to achieve high resolution at sharply lower costs. Take a look at this list of astronomical interferometers working from the visible to the infrared and you'll see how widely spread the technique has become as we've moved from earlier long wavelength observations (including the Very Large Array and MERLIN) toward optical installations and submillimeter interferometers and, now under construction, the Atacama Large Millimeter Array. Observing Earth-like planets from space has often been studied in terms of a space-based array, with separated spacecraft operating in tandem, as in the infrared interferometer concept shown in this image (Credit: JPL). Both the now stalled Terrestrial Planet Finder and the canceled Darwin mission from ESA were looking at interferometry concepts that would have used a...

HD 209458b is perhaps the most persistently studied exoplanet we have, a transiting 'hot Jupiter' that has already revealed a slew of its secrets, including the detection of carbon dioxide, water vapor and methane. I confess that it sometimes seems like black magic to me that we are able to ferret out the signature of organic compounds on worlds we cannot even see. But the transit method is fruitful, and when scientists examine the light of the star during a planetary transit, the tiny portion of that light filtering through the planet's atmosphere can be analyzed. In the case of HD 209458b, we're talking about a three hour transit, one that occurs every 3.5 days as this 'hot Jupiter' makes its rounds. Now we learn that the carbon dioxide detected here can also be studied in terms of its velocity. The result: We have indications of a vast storm, a wind flow that's moving at speeds that defy the imagination. Ignas Snellen (Leiden Observatory, The Netherlands) led the team that...

The release of the first 43 days of Kepler data has demonstrated just how powerful a planet-hunting technology we've put into space. Listen to principal investigator William Borucki (NASA Ames) in a video released yesterday by NASA television: "We're releasing data on 156,000 stars that we've been monitoring with the Kepler mission for 43 days, the first dataset. In these data are some 750 planetary candidates. Some of those are actual planets, some are false positives. Our science team is looking at 400 of those candidates with ground-based telescopes, to figure out which are planets, which aren't." Borucki assumes about fifty percent of the candidates will be false positives, eclipsing binary stars, starspots, or other misleading signals. Now it's in the hands of ground-based telescopes in the Canary Islands, Texas, Arizona and Hawaii to comb through these findings to make the call. The team is also releasing the data for the remaining 350 candidates to the world community of...

One of the problems with determining how planets form is the nature of the dusty gas-rich disks that surround their stars. We're learning as we study these things that the disks around young stars disperse quickly in astronomical terms, within several million years. Thus finding a massive planet around a young star like Beta Pictoris is noteworthy. It demonstrates that such planets can form in short-order. What's doubly fascinating about the new find is that this planet was discovered by direct imaging techniques, and that it is as close to its star as Saturn is to ours. Have a look at the imagery below, made using the European Southern Observatory's Very Large Telescope and an adaptive optics instrument that removes atmospheric blurring and other effects. It's a composite showing the faint source in the 2003 image and contrasting it with the motion of the object as seen in the autumn of 2009. The object can be seen to have moved to the other side of the disk. As we only have direct...