Continuing with what promises to be a seriously interesting week in exoplanet studies, I want to home in this morning on PH1, a planet that reminds us how much the public has become involved in ongoing science thanks to the widespread distribution of computer power. As presented at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Reno (NV), the finding pairs volunteers working with the crowdsourced Planet Hunters project with an international team of professional astronomers led by Yale University's Meg Schwamb. The volunteers -- Kian Jek of San Francisco, California, and Robert Gagliano of Cottonwood, Arizona -- were the first to spot the telltale lightcurve of a transit, which was then confirmed by astronomers using the Keck instruments at Mauna Kea (Hawaii). What the investigation uncovered was a gas giant about 6.2 times the radius of the Earth, putting it into Neptune-territory. But what really flags the attention is the fact that...

Because it's going to be an interesting week for exoplanet studies (for reasons I'll talk about soon, though not today), I'll lead off with some thoughts on eta-Earth, defined as the fraction of Sun-like stars with a planet like Earth orbiting them. We have a lot to learn about the frequency of terrestrial worlds, and as Philip Horzempa points out in a recent article for The Space Review, the image that's gradually emerging is of fewer 'Earths' than Carl Sagan once estimated when he said in the 1980s that half of all stars could have a planet like our own. Image: Artists' concepts of small exoplanets compared to our own planets Mars and Earth. As Kepler continues to hunt, how can we move beyond its findings to learn more about terrestrial planets around much closer stars? Credit: NASA/JPL-Caltech With Kepler's continuing datastream and improving ground-based instrumentation, we're learning more about planet distribution, but Horzempa notes that even now, estimates of Earth analogs...

Gliese 581d seems more and more to be considered a habitable zone planet, as Siddharth Hegde (Max Planck Institute for Astronomy) and Lisa Kaltenegger (Harvard-Smithsonian Center for Astrophysics) describe it in a new paper. They're homing in on how to characterize a rocky exoplanet and point to HD 85512b and Gliese 667Cc as well as Gl581d as examples, but they also assume that we'll be seeing more and more habitable zone worlds as the Kepler mission continues its work, so how we learn more about these planets becomes a big issue. In the absence of missions like Terrestrial Planet Finder or ESA's Darwin, which would allow us to analyze an exoplanetary atmosphere for biomarkers, what else can we do to find the places where life exists? Hegde and Kaltenegger look hard at a planet's color to find the answer. Specifically, they're interested in what's known as a color-color diagram, which takes advantage of the fact that an object can be observed at a variety of wavelengths, with a...

New findings from the Herschel space observatory demonstrate how effective the infrared telescope can be at teasing out details of distant planetary systems. At issue is the system around Beta Pictoris, a young star (12 million years old) some 63 light years from the Earth. We’re looking at planetary system formation in progress here, with a single gas giant planet and a dusty debris disk that may be the forerunner of a disk much like our own Edgeworth/Kuiper Belt, the collection of icy bodies that orbits outside the orbit of Neptune. Ben de Vries (KU Leuven) is lead author of the paper on the new Herschel data, which examines the composition of dust in the outer regions of the Beta Pictoris disk. The study, reported today in Nature, presents a photometric and spectral analysis of dust particles produced when planetesimals in this region collide. The key player here is olivine, a mineral associated with protoplanetary disk material around newborn stars. The olivine found around Beta...

Super-Earths are exciting finds. The more of them we discover, the more likely it seems that life is abundant in the cosmos. But new work examining the viscosity and melting temperature of mantle rock is casting a different aura over super-Earths. Rather than being planets much like the Earth but simply more massive -- worlds characterized by thick atmospheres, plate tectonics, volcanic activity and magnetic fields -- they may differ in fundamental ways. With internal pressures tens of times higher than those found in Earth's interior, large viscosities and melting temperatures could have adverse consequences on the planet's habitability. The potential effects extend as far as the core of the planet, which may not even exist. In a presentation at the European Planetary Science Congress on September 26, Vlada Stamenkovic (Massachusetts Institute of Technology) noted that the average super-Earth may in fact be undifferentiated; i.e., it may not have separated into a metallic core and a...

Among the more interesting items coming out of the XXVIII General Assembly of the International Astronomical Union (IAU) in Beijing is news of a circumbinary system containing two planets. We've seen circumbinary worlds before -- Kepler-16b is a planet orbiting not one but two stars, as are Kepler-34b and Kepler-35b. There was a time that the idea of a planet orbiting two stars, as opposed to orbiting one or the other of two stars in a binary system, seemed unlikely. Now we have a multiple-planet system in exactly this configuration. It's an interesting one, too. Some 4900 light years from Earth in the constellation Cygnus, the two stars orbit each other roughly every 7.5 days. One of the stars is fairly similar to the Sun, though about 15 percent less bright, while the other is an M-dwarf about a third of Sol's size and 175 times fainter. Of the two planets, one -- Kepler-47b -- is three times the diameter of Earth and eight times its mass, orbiting the twin stars every 49 days. The...

Polish astronomer Aleksander Wolszczan (Penn State) is best known as the discoverer of the first confirmed planet outside our Solar System. That was back in the early 1990s, when Wolszczan was working with Dale Frail (NRAO), using observations from the Arecibo dish to demonstrate that the pulsar PSR B1257+12 was orbited by two planets. These are relatively small worlds (3.9 and 4.3 Earth masses respectively), and in an era where new planet candidates number in the thousands, it’s easy to forget how striking Wolszczan’s work appeared at the time, and how it gave impetus to the developing exoplanet hunt. A pulsar planet looks to be an extremely inhospitable place, but learning how planets are distributed among the stars involves studying every conceivable kind of world. Wolszczan’s latest work targets an equally hostile environment, the former habitable zone of a star that has begun expanding into a red giant. The star, BD+48 740, has 11 times the Sun’s radius and is significantly...

Ponder how our planet got its water. The current view is that objects beyond the 'snow line,' where water ice is available in the protoplanetary disk, were eventually pushed into highly eccentric orbits by their encounters with massive young planets like Jupiter. Eventually some of these water-bearing objects would have impacted the Earth. The same analysis works for exoplanetary systems, but the amount of water delivered to a potentially habitable planet depends, in this scenario, on the presence of giant planets and their orbits. Dorian Abbot (University of Chicago) and colleagues Nicolas Cowan and Fred Ciesla (both at Northwestern University) note the consequences of this theory of water delivery. One is that because low mass stars are thought to have low mass disks, they would have fewer gas giants and would produce less gravitational scattering. In other words, we may find that small planets around M-dwarfs are dry. On the other hand, solar-mass stars and above could easily have...

Barnard's Star has always gotten its share of attention, and deservedly so. It was in 1916 that this M-class dwarf in Ophiuchus was measured by the American astronomer Edward Emerson Barnard, who found its proper motion to be the largest of any star relative to the Sun. That meant the star soon to be named for him was close to us, and unless we're surprised by a hitherto unobserved brown dwarf, Barnard's Star remains the closest star to our Sun after the Alpha Centauri triple system. Stick around long enough and Barnard's Star will close to within 3.75 light years, but even if you make it to 10,000 AD or so, the star will still be too faint to be a naked eye object. Image: Barnard's Star, with proper motion demonstrated, part of an ongoing project to track the star. This image shows motion between 2004 and 2008. Credit: Paul Mortfield & Stefano Cancelli/The Backyard Astronomer. Peter van de Kamp, working at Swarthmore College, had been looking for wobbles in the position of Barnard's...

Gliese 581 is an utterly maddening star, one that continues to tantalize us with potential habitability. The case of Gl 581g, examined here yesterday, is only the latest wrinkle, but it's in some ways the most frustrating. We're studying planets we cannot actually see, inferring their presence through the tiniest of variations in starlight caused by the planets' gravitational effect on their star. Adjust planetary orbits here in the direction of eccentricity and you can make Gl 581g disappear. Assume circular orbits and you can produce a habitable zone super-Earth. I think we'll still be arguing about this one for some time, but in the interim the question will lose a lot of its force. Remember, the reason we're so excited about Gl 581g is that it would become the closest planet with the possibility of liquid water at the surface (possibly joined by Gl 581d in the same system). But Jean Schneider's Exoplanet.eu catalog shows 777 confirmed planets this morning, and Kepler has pulled...

Not long ago, while making a presentation about possible destinations for an interstellar probe, I called Gl 581d the most likely candidate for habitability yet discovered among nearby stars. I knew the planet was problematic, perhaps too far on the outer edge of the habitable zone to be a realistic candidate, although this seems to depend on a variety of factors including atmospheric modeling. But what I had really been pondering in deciding whether or not to include Gl 581d in the talk was whether its purported sister world, Gl 581g, should be brought into play. Steven Vogt (UC-Santa Cruz) and colleagues were getting ready to distribute their new paper making a further case for a super-Earth in the habitable zone, one that seemed to be ideally placed for liquid water to exist on the surface. Bring that into the discussion? I decided against it, because the controversy over this world continues and Centauri Dreams seems a better venue than a short public talk to get into the...

Finding new worlds with Kepler is an absorbing occupation, but the one thing missing from most exoplanet news is proximity. While we continue to search for planets around the Alpha Centauri stars, the closest candidate I know about is the gas giant thought to orbit Epsilon Eridani, some 10.5 light years out. If you're looking for potential habitability, you have to extend all the way out to Gliese 581 (almost twice the distance), where planets are plentiful and there is at least the chance (GL 581d) that one skirts the edge of the habitable zone. There are probably many planets closer than 20 light years, but we don't have the tools in space to find them easily. Kepler, you'll recall, studies a field of stars in Cygnus, Lyra and Draco, the goal being to develop a statistical approximation of the prevalence of Earth-sized planets in the galaxy. Looking out along the Orion arm, Kepler is watching stars anywhere from 600 to 3000 light years away. In fact, fewer than 1 percent of the...

Is the discovery of oceans on planets orbiting distant stars within our reach? Finding such an ocean would be of immense interest from an astrobiological perspective because water on the surface is the traditional marker for a habitable zone. Astrobiology Magazine has just written up work by Nicholas Cowan (Northwestern University) and colleagues, who have been looking at the ways we might detect such oceans. The researchers are thinking ahead to a time when we have an actual image of a terrestrial world to look at, even if that image is little more than the 'pale blue dot' Voyager saw in its famous portrait of the Solar System. When we have identified that 'dot,' we can do a lot with it by studying the way its light varies as it orbits its star. Let's assume we deploy a starshade and use it in conjunction with the James Webb Space Telescope to block the light of the star and reveal the faint signature of the planet. A disk tens of meters wide with petal-like extensions, the...

Although I want to move on this morning to some interesting exoplanet news, I'm not through with fusion propulsion, not by a long shot. I want to respond to some of the questions that came in about the British ZETA experiment, and also discuss some of Rod Hyde's starship ideas as developed at Lawrence Livermore Laboratory in the 1970s. Also on the table is Al Jackson's work with Daniel Whitmire on a modified Bussard ramjet design augmented by lasers. But I need to put all that off for about a week as I wait for some recently requested research materials to arrive, and also because next week I'm taking a short break, about which more on Monday. For today, then, let's talk about an advance in the way we study distant solar systems, for we're finding ever more ingenious ways of teasing out information about exoplanets we can't even see. The latest news comes from the study of Tau Boötis b, a 'hot Jupiter' circling its primary -- a yellow-white dwarf about 20 percent more massive than...

Astronomical surprises can emerge close to home, close in terms of light years and close in terms of time. Take NGC 6774, an open cluster of stars also known as Ruprecht 147 in the direction of Sagittarius. In astronomical terms, it's close enough -- at 800 to 1000 light years -- to be a target for binoculars in the skies of late summer. In chronological terms, the cluster has had a kind of re-birth in our astronomy. John Herschel identified it in 1830, calling it 'a very large straggling space full of loose stars' and including it in the General Catalog of astronomical objects. But NGC 6774 remained little studied, and it took a more intensive look by Jaroslav Ruprecht in the 1960s to give the cluster both a new name and a firmer identity. This loose group of stars had long been thought to be an asterism, a chance alignment of stars that when seen from the Earth gave the impression of being a cluster. Ruprecht realized this was no asterism, and now new work with the MMT telescope in...

I've always had an interest in old travel books. A great part of the pleasure of these journals of exploration lies in their illustrations, sketches or photographs of landscapes well out of the reader's experience, like Victoria Falls or Ayers Rock or the upper reaches of the Amazon. Maybe someday we'll have a travel literature for exoplanets, but until that seemingly remote future, we'll have to use our imagination to supply the visuals, because these are places that in most cases we cannot see and in the few cases when we can, we see them only as faint dots. None of that slows me down because imagined landscapes can also be awe-inspiring. This morning I'm thinking about what it must be like on the molten surface of the newly discovered world Kepler-36b, a rocky planet 1.5 times the size of Earth and almost 5 times as massive. This is not a place to look for life -- certainly not life as we know it -- for it orbits its primary every 14 days at a scant 17.5 million kilometers. But if...

In astronomy, the word 'metals' refers to anything heavier than hydrogen and helium. Stars fuse hydrogen into helium and from there work their way into the higher elements until hitting iron, at which point the end quickly comes, with 'star stuff,' as Carl Sagan liked to put it, being flung out into the universe. Through stellar generations we can trace a higher concentration of the heavier elements as stars are born from the materials of their predecessors. And we've learned that those metal-rich stars are the most likely to produce gas giants like Jupiter and Saturn. What's intriguing is the issue of smaller planets and the conditions for their formation. After all, the content of the disk from which planets are formed parallels the metallicity of the host star. I'm looking at new research from Lars A. Buchhave (Niels Bohr Institute/University of Copenhagen) into planet formation, using data from the Kepler telescope. In Buchhave's words: "We have analysed the spectroscopic...

The success of the Kepler mission in sifting through a field of more than 150,000 stars to locate transiting planets is undeniable, and the number of planets thus far discovered has been used to estimate how often planets occur around stars like the Sun. Now comes a paper to remind us that statistical analysis based on Kepler results assumes that most of the planet candidates are real and not false positives. Alexandre Santerne, a graduate student at the University of Aix-Marseille, has worked with a team of researchers to study the false positive rate for giant planets orbiting close to their star. 35 percent of these Kepler candidates may be impostors. The problem is that eclipsing binaries can mimic planetary transits, which is why scientists perform follow-up radial velocity studies or use transit timing variations (TTV) to confirm the existence of the planet. Another technique is to systematically exclude all possible false positive scenarios to a high level of confidence....

While we wait for the last transit of Venus of the century, it's worth remembering how tricky transit studies can be when we push them out to exoplanetary distances. You would think that catching a transit of a planet like Venus, closer to us than the Sun, would be simplicity itself, but the orbital planes of Venus and the Earth are not precisely enough aligned to allow for more than a pair of transits followed by over a century of waiting for the next. I've just received a copy of Mark Anderson's The Day the World Discovered the Sun (Da Capo Press, 2012) and will be writing about 18th Century transit studies and their impact in coming weeks. The transits Anderson writes about and the expeditions that ranged the globe to study them played a role in helping astronomers understand the dimensions of the Solar System. And you can see that if Venus is a challenge, tracking planets around other stars will push our technology to its limit. Nonetheless, we're getting quite good at teasing...

When you're looking for signs of an extraterrestrial civilization, you can take two basic approaches. Think back to Frank Drake's initial SETI experiment at Green Bank in 1960, when because of limited resources and time he chose specific targets: Epsilon Eridani and Tau Ceti. The choice made sense at the time because both were nearby stars and SETI, fresh off the classic paper "Searching for Interstellar Communications" by Philip Morrison and Giuseppe Cocconi, was just beginning to define a methodology. Drake studied his targets near the 1.420 GHz frequency -- the 21 centimeter hydrogen line -- that the authors had suggested. Of course, sky surveys are also possible, of which SETI@home may be the most widely known. Here the idea is to make no assumptions whatever about the location of a SETI signal and observe the entire sky. SERENDIP (Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations) is an attempt, for example, to analyze radio telescope data...