The confirmation of a planet circling two stars, recounted in these pages yesterday, is actually the result of a long process. Jean Schneider (CNRS/LUTH - Paris Observatory) noted in a follow-up comment to the Kepler-16b story that investigation of such systems dates back to 1990 (see citation below), while Alex Tolley has pointed out that the great space artist Chesley Bonestell was painting imaginary planets orbiting binary stars fully sixty years ago. So the idea isn't new, but the confirmation was obviously useful, and in more ways than we might have expected. For one thing emerging from the Kepler-16b paper is that the smaller of the two stars in this binary system, an M-dwarf, is now the smallest low-mass star to have both its mass and radius measured at such precision. The question of stellar mass and M-dwarfs is significant because a new paper by Philip Muirhead (Cornell University) and colleagues goes to work on the parameters of low-temperature Kepler planetary host stars...

I'm just back from a long trip and am only now catching up on some of the news stories from late last week. Among these I should mention the discovery of the world with the double sunset, identified through Kepler data and reminiscent of the famous scene from Star Wars, where Luke Skywalker stands on the soil of Tatooine and looks out at twin suns setting. I remember carping about the scene when it first came out because it implied a planet that orbited two stars at once. Now we have confirmation that such a configuration is stable and that planets can exist there. Kepler-16 isn't a habitable world by our standard definition, but much more like Saturn, cold and gaseous. One of the stars it circles is a K dwarf of about 69 percent the mass of our Sun, while the other is a red dwarf of about 20 percent solar mass. Some 220 light years away in the direction of the constellation Cygnus, the system is fortuitously edge-on as seen from Earth, allowing Kepler scientists to identify the...

The largest variations in brightness ever seen on a cool brown dwarf have turned up on the brown dwarf 2MASS 2139 (known as 2MASS J21392676+0220226 to its friends). The findings, reported at the Extreme Solar Systems II conference in Jackson Hole, Wyoming, show a remarkable 30 percent change in brightness in a period of just under eight hours. The assumption is that brighter and darker patches of atmosphere are periodically moving into view as the brown dwarf rotates. In fact, Ray Jayawardhana (University of Toronto), co-author of the paper on this work, thinks one possibility is something similar to what we see in our own Solar System. “We might be looking at a gigantic storm raging on this brown dwarf, perhaps a grander version of the Great Red Spot on Jupiter in our own solar system,” says Jayawardhana, “or we may be seeing the hotter, deeper layers of its atmosphere through big holes in the cloud deck.” Image: Astronomers have observed extreme brightness changes on a nearby brown...

This is a big week for exoplanet news with the continuing presentations at the Extreme Solar Systems II conference in Wyoming. But I'm going to have to be sporadic with posts this week because of ongoing commitments. The papers for the upcoming 100 Year Starship Symposium are due within days, which is a major driver, but I've also got even more important matters unrelated to my interstellar work to attend to. I'll probably be able to get another post off this week, and then we can catch up a bit next week. For now, here's a story I want to get in that involves things we can't see. Remember 'Invisible Invaders'? This 1959 drive-in classic involved aliens you can't see in spaceships that are likewise transparent, arriving on Earth to take over the bodies of the recently deceased. John Agar and Robert Hutton spent a lot of this movie chasing a comely physicist (Jean Byron) when they weren't working out a way to foil the aliens' plans to take over our planet in three days. Knowing my...

With the online press conference re new results from the HARPS spectrograph (High Accuracy Radial Velocity Planet Searcher) now being discussed, I want to pause for a moment before getting into them to mention the ongoing Extreme Solar Systems II conference, which runs until the 17th at quite a venue, Jackson Lake Lodge in Wyoming. The tentative program is available online, with the welcome news of new HARPS and Kepler results and any number of intriguing talks on everything from debris disk imaging around nearby stars to core accretion models. We’ll doubtless be talking about some of these findings in coming weeks. But for now, on to the HARPS discussion at the Wyoming conference. The take-away quote from today’s news was this, from Michel Mayor (University of Geneva): “The harvest of discoveries from HARPS has exceeded all expectations and includes an exceptionally rich population of super-Earths and Neptune-type planets hosted by stars very similar to our Sun. And even better —...

We've been assuming all along that it would take the Kepler mission three years-plus to detect true Earth analogues, meaning planets orbiting Sun-like stars at about the Earth's orbital distance. Now it turns out that figure may have to be extended, as this article in Nature makes clear. Author Ron Cowen points out that a close analysis of approximately 2,500 of the tens of thousands of stars in the Kepler field are flickering more than expected, and that spells trouble. Image: Kepler's field of view superimposed on the night sky. Credit: Carter Roberts. The reason: The dip in starlight signalling the presence of a planet can be masked by the unexpected noise in the Kepler data. As described by Kepler scientist Ron Gilliland (Space Telescope Science Institute), the signal of an Earth analogue -- assuming a star much like the Sun -- should be a drop of about 85 parts per million when the planet passes in front of its star, lasting a statistical average of 10 hours, and occurring once...

One of the problems with building a backlog of stories is that items occasionally get pushed farther back in the rotation than I had intended. Such is the case with an article in Astrobiology Magazine that talks about how much of a factor a large moon may be in making a planet habitable (thanks to Mark Wakely for passing the link along). It's an interesting question because some have argued that without our own Moon, the tilt of the Earth's axis, its 'obliquity,' would move over time from zero degrees to 85 degrees, a massive swing that would take the Sun from a position over the equator to one where it would shine almost directly over one of the poles. The resulting climate changes would be severe, potentially affecting the development of life. The thinking is that just as the direction of the tilt of a planet varies with time -- astronomers say that it 'precesses' -- so does the orbital plane of the planet. The gravity of a large moon like ours affords a stabilizing effect by...

A planet orbiting the star GSC 03549-02811, about 750 light years away in direction of the constellation Draco, is showing us a new way of extracting information about a distant system. The planet is a gas giant called TrES-2b, discovered by the Trans-Atlantic Exoplanet Survey in 2006. Studying the star using data from Kepler observations over a span of 50 orbits, David Kipping (Harvard-Smithsonian Center for Astrophysics) and David Spiegel (Princeton University) have detected the faint brightness variations caused by planetary phase changes during its orbits. The light from the planet dims and brightens as it moves through its phases around the star. "In other words, Kepler was able to directly detect visible light coming from the planet itself," says Kipping, and what we've learned is that TrES-2b is remarkably dark, reflecting less than one percent of the sunlight falling on it. The planet is blacker than any moon or planet in our solar system, as black as coal, or in Kipping's...

We don't know whether life can exist on a planet circling a red dwarf, but as reported in these pages frequently in the last few years, there have been studies showing that liquid water could persist on the surface of such planets despite the fact that they would most likely be tidally locked, with one side always facing their star. So the potential is there, but we also have to account for flare activity and the question of how life might adapt to it. Perhaps there are protective mechanisms that might shield such planets from the worst such eruptions, a possibility now raised by Ofer Cohen (Harvard-Smithsonian Center for Astrophysics). Cohen and team have recently gone to work on planets of a far different kind -- hot Jupiters crowded up in tight orbits around more Sun-like stars -- but the work on gas giants is intended to lead on to a close look at red dwarf planets in similar proximity to violent stellar events. Until that study is complete, we can learn from their work on what...

Although we talk about space-based observatories 'discovering' planets, the actual process is much more complex. Data from CoRoT, for example, must be validated carefully to make sure that what is being observed is actually a planet. That means turning to follow-up observations by ground-based telescopes, so that the whole package of photometric and spectroscopic data can confirm the planet and help us understand the system in which it orbits. New results from the Second CoRoT Symposium in Marseille are in, adding another 10 planets to CoRoT's roster. Thus we get seven 'hot Jupiters,' a planet smaller than Saturn (CoRoT-22b), and a pair of Neptune-mass planets (CoRoT-24b and CoRoT-24c) orbiting the same star. These gaseous planets come in a wide range of densities, from one that is roughly as dense as Saturn to higher densities comparable to Mars. It's also an interesting mix in terms of age. CoRoT-17b is, at 10 billion years, twice as old as the Sun, while CoRoT-18b is still a...

Canada's MOST space telescope (Microvariability & Oscillations of STars) has been used to put some constraints on the super-Earth GJ 581e. The work was discussed at this week's meeting of the Canadian Astronomical Society in Ontario. Planet e is the innermost world among the multiple planets orbiting the star, and the least massive (with a minimum mass twice that of the Earth). Thus far it has been the Doppler method, measuring wavelength shift in the star's spectral lines, that has identified the four uncontroversial planets: GJ 581 b, c, d and e. I use the term 'uncontroversial' because of the ongoing debate over two other possibilities, not yet confirmed, one of which (GJ 581 g) was thought to be in the star's habitable zone and announced as such to widespread media attention. The issue remains in doubt but I'm hearing little support for the two latter planets. Nonetheless, the GJ 581 system has stayed in the news because of habitable zone questions, the latest involving GJ 581 d,...

Be aware of two meetings of relevance for interstellar studies, the first of which takes place today at the Massachusetts Institute of Technology. There, a symposium called The Next 40 Years of Exoplanets runs all day, with presentations from major figures in the field -- you can see the agenda here. I bring this up because MIT Libraries is planning to stream the presentations, starting with Dave Charbonneau (Harvard University) at 0900 EST. Those of you who've been asking about Alpha Centauri planet hunts will be glad to hear that Debra Fischer (Yale University), who is running one of the three ongoing Centauri searches, will be speaking between 1130 and 1300 EST. The poster for this meeting reminds me of the incessant argument about what constitutes a habitable planet. It shows two kids in a twilight setting pointing up at the sky, their silhouettes framed by fading light reflected off a lake. One of them is saying 'That star has a planet like Earth." An asterisk reveals the...

Kepler is a telescope that does nothing more than stare at a single patch of sky, described by its principal investigator, with a touch of whimsy, as the most boring space mission in history. William Borucki is referring to the fact that about the only thing that changes on Kepler is the occasional alignment of its solar panels. But of course Borucki's jest belies the fact that the mission in question is finding planets by the bushel, with more than 1200 candidates already reported, and who knows how many other interesting objects ripe for discovery. Not all of these are planets, to be sure, and as we'll see in a moment, many are intriguing in their own right. But the planets have center stage, and the talk at the American Astronomical Society's 218th meeting has been of multiple planet systems found by Kepler, after a presentation by David Latham (Harvard-Smithsonian Center for Astrophysics). Of Kepler's 1200 candidates, fully 408 are found in multiple planet systems. Latham told...

Gravitational microlensing to the rescue. We now have evidence for the existence of the rogue planets -- interstellar wanderers moving through space unattached to any star system -- that we talked about just the other day. It's been assumed that such planets existed, because early solar systems are turbulent and unstable, with planetary migrations like those that lead to 'hot Jupiters' in the inner system. Moving gas giants into orbits closer to their star would cause serious gravitational consequences for other worlds in the system, ejecting some entirely. But while we've been thinking in terms of detecting such worlds through auroral emissions like those produced by Jupiter, researchers at two microlensing projects have made a series of detections by using gravity's effects upon spacetime. Specifically, a stellar system passing in front of a far more distant background star will warp the light of the background object. The resulting magnification and brightening flags the presence...

Imagine a planet far more massive than Jupiter and spinning faster than Jupiter's 10 hour rotation. Throw in a large nearby moon and the associated auroral effects that would occur as the moon moved through fields of plasma trapped in the planet's magnetic field. The scenario isn't all that different from what we see happening between Jupiter and Io. But here's the kicker: Put planet and moon far away from any star, a rogue planet scenario of the kind recently discussed by Dorian Abbot and Eric Switzer, who called such rogue planets 'Steppenwolfs.' I jumped on that idea in a Centauri Dreams post last February because interstellar planets have always fascinated me. Abbot and Switzer were interested in whether a rogue planet could support life, finding in their paper that a planet just 3.5 times as massive as the Earth, and with the same basic composition and age, could sustain a liquid ocean under layers of insulating water ice and frozen atmosphere. But our rogue gas giant offers...

My friend Adam Crowl, a polymath if there ever was one, is working hard on Project Icarus and keeping an eye on the exoplanet situation. When you're working on a starship design, no matter how theoretical, a major issue is the choice of targets, and the study of Kepler planets we looked at yesterday caught Adam's eye some time ago. We're not finding as many planets in the habitable zone thus far in the Kepler hunt as we might hope to, given that the ideal would be a habitable world somewhere within reach of near-future technologies of the kind that Icarus represents. Sure, Kepler's target stars are much further away in most cases, but the mission is giving us a useful statistical sampling from which we can generalize. Working with the data from Lisa Kaltenegger and Dimitri Sasselov's paper, Adam thus takes a back-of-the-envelope stab at the galactic population of terrestrial worlds, knowing that Kepler is far from through, as we're moving into the domain of planets with longer...

A habitable zone can be defined in many ways, but for our immediate purposes, defining it with reference to liquid water on a planetary surface makes sense. Sure, we believe that life could exist beneath the surface on places like Europa, where surface water is out of the question, but the key issue is this: Are there atmospheric features that we could use to make the call on habitability? It's an important issue because with our current and near-future technology, this is how we can plan to investigate life on planets around other stars. We can study exoplanetary atmospheres already and we're getting better, but we can't drill through exoplanetary ice. A new paper from Lisa Kaltenegger and Dimitri Sasselov (Harvard Smithsonian Center for Astrophysics) gets into these questions by looking at how to evaluate habitability, studying different kinds of planetary atmospheres and developing model calculations. The intent is to apply these ideas to the habitable planet candidates, 54 in...

Over 900 stars have been found that show signs of a debris disk, a circumstellar disk of dust and debris orbiting the star. It takes less than 10 million years for the gaseous content of these disks to dissipate, leaving the dusty disk behind. You can think of the Kuiper Belt in our own system, but the analogy would be imprecise in a crucial way, for most of these disks show much more dust. In fact, explaining the difference between the debris disks of other stars and what we see in our own system is instructive, and it may offer clues to terrestrial planet formation elsewhere. For we're learning that long-lasting cold dust points to a system-wide stability that is probably crucial. At issue is the question of what happens when gas giants cause gravitational instabilities in a young system. Sean Raymond (Université de Bordeaux) and collaborators tackle the question in a new paper that looks at how planets emerge from circumstellar disks. Inner disks form rocky planets in 10 to...

We've been finding planets using radial velocity methods -- analyzing the gravitational effects of planets around their stars -- since the mid-1990s, and the Kepler mission has brought the transit method to the fore, looking at the lightcurves of stars when planets pass in front of them as seen from Earth. Now we have new information about a transiting planet, 55 Cancri e, in a multiple planet system, information that has been developed by reanalyzing earlier radial velocity data. The new techniques were applied by Rebekah Dawson (Harvard-Smithsonian Center for Astrophysics), working in tandem with Daniel Fabrycky (UC-Santa Cruz) to predict the orbit of 55 Cancri e. Earlier radial velocity data on the planet had suggested a tight orbit of 2.8 days, but the new analysis pegged the orbit at something less than 18 hours. The proximity to the central star meant that the chances of seeing a transit were higher than thought (the probability moved from 13 percent to 33 percent), leading to...