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...

It's no surprise that the techniques we're using to look for moons around exoplanets should start turning up new planets on their own. We're still looking for that first exomoon, but a team of researchers working with the Hunt for Exomoons with Kepler (HEK) project has found transit variations that have revealed a second planet around a star already known to have one transiting planet. The star is the intriguing KOI-872 (KOI stands for Kepler Object of Interest), the data on which were recently released by the Kepler team and analyzed swiftly by HEK. Kepler's transit methods examine the change in starlight when an exoplanet passes in front of the star being observed. This lightcurve, however, can tell more than a single tale. David Kipping (Harvard-Smithsonian Center for Astrophysics) is head of HEK and second author of the paper on the new work, which was published online today in the journal Science: "For a planet following a strictly Keplerian orbit around its host star, the...

I cannot live without good coffee, and that means fresh beans ground right before brewing, and either manual drip or French press extraction. Every morning after publishing Centauri Dreams I make a couple of cups and go out on the deck to rest my eyes and ponder the state of things before hitting the books for background research in the afternoon. Various thoughts about what to write next always come to me, but yesterday I mused about Enrico Fermi, the legendary Italian physicist who, among so much else, left us with a great unanswered question: Where are they? If it’s so easy for the universe to make intelligent species, why is SETI coming up so short? Where are they indeed? The day was gorgeous, the air filled with birdsong, temperatures in the mid-60s and a mild breeze. What better setting to be immersed in, thinking about where life emerges and when? I imagined Fermi sitting across from me with a cup of my Costa Rica Tres Rios in his hand, wondering what he might say about the...

Although we haven’t yet found any planets around Proxima Centauri, it would be a tremendous spur to our dreams of future exploration if one turned up in the habitable zone there. That would give us three potential targets within 4.3 light years, with Centauri A and B conceivably the home to interesting worlds of their own. And the issue we started to look at yesterday -- whether Proxima Centauri is actually part of the Alpha Centauri system or merely passing through the neighborhood -- has a bearing on the planet question, not only in terms of how it might affect the two primary stars, but also because it would tell us something about Proxima’s composition. A Gravitationally Bound System Greg Laughlin makes this case in the systemic post I referred to yesterday. It was Laughlin and Jeremy Wertheimer (UCSC) who used data from ESA’s Hipparcos mission to conclude that Proxima was indeed bound to Centauri A and B. Here I want to quote the conclusion of the duo’s paper on the matter,...

Let's start the week with a reminder about Debra Fischer's work on Alpha Centauri, which we talked about last week. There are several ongoing efforts to monitor Centauri A and B for planets and, given the scrutiny the duo have received for the past several years, we should be getting close to learning whether there are rocky worlds in this system or not. Fischer's continuing work at Cerro Tololo involves 20 nights of observing time that her grant money can't cover. Private donations are the key -- please check the Planetary Society's donation page to help if you can. While interest in the Alpha Centauri system is high, the small red dwarf component of that system has been getting relatively little press lately. But I don't want to neglect Proxima Centauri, which as far as we know is the closest star to the Earth (some 4.218 light years away, compared to Centauri A and B's 4.39 light years). From a planet around Centauri B, it would be hard to know that Proxima (also known as Alpha...

The Kepler mission's exoplanet discoveries have been so numerous that an extension of the mission seemed all but inevitable. At the same time, bureaucracies can be unpredictable, which is why it was such a relief to have the Senior Review of Operating Missions weighing in with an extension recommendation, one followed up by NASA with extensions not just for Kepler but also for the Spitzer telescope and the US portion of ESA's Planck mission. Kepler's extension runs through fiscal 2016 (subject to review in 2014), allowing for plenty of time to home in on Earth-sized planets in the habitable zone around stars like our Sun. While Kepler's scheduled mission duration was 3.5 years, the mission was intended to be extendible to 6 years or more and this news is more than satisfying. But of course while we continue to monitor the Kepler work, we're following numerous other exoplanet stories including the European Southern Observatory's observations of the prolific star HD 10180, a Sun-like...

The idea of 'deep time' exerts an abiding fascination. H.G. Wells took us forward to a remote futurity when his time traveler looked out on a beach dominated by a red and swollen Sun. But of course deep time goes in the other direction as well. I can remember wanting to become a paleontologist when I discovered books about the world of the dinosaurs, my mind reeling from the idea that the world these creatures lived in was as remote as any distant star. Paleontology was a grade-school ambition I never followed up on, but the Triassic and Jurassic eras still have a hold on my imagination. In a SETI context, deep time presents challenges galore. Charles Lineweaver's work offers up the prospect that the average Earth-like planet in our galactic neighborhood may well be far older than our own -- Lineweaver calculates something like an average of 1.8 billion years older. Would a civilization around such a star, if one could survive without destroying itself for so long, have anything it...

Red dwarfs are all over the news thanks to an announcement by the European Southern Observatory. Results from a new HARPS study show that tens of billions of planets not much larger than Earth are to be expected in the habitable zones around this class of star. The finding reinforces the growing interest in M-class stars and becomes especially interesting when you realize that faint red stars like this make up as much as 80 percent of the stars in the Milky Way. That leaves plenty of room for astrobiology, depending on factors we need to discuss below. Do we suddenly have a close destination for a potential interstellar probe? Well, Barnard’s Star has always been in the running for an early mission because of its relative proximity to us at 5.94 light years. But we still have no word on planets there (despite a much publicized but soon discredited set of observations from a 1969 paper). Proxima Centauri is available at 4.2 light years, but we have yet to learn whether it has planets....

Figuring out how planets form is an old occupation, with the basic ideas of planetary accretion going back several centuries, though tuned up, to be sure, in the 1970s and tweaked ever since. In a disk of gas and dust orbiting a young central star, dust grains begin to clump together, eventually forming planetesimals. Accretion models assume that these small planetesimals bang into each other and gradually grow. The assumption is that in the inner system at least temperatures are hot and the era of planet formation occurs well after the central star has formed. Image: Artist's conception of a protoplanetary disk. Credit: NASA/JPL-Caltech/T. Pyle. Adjust for distance from the star and subsequent planetary migration in the gas/dust disk and you can come up with a system more or less like ours, with rocky inner worlds and gas giants out beyond the snow line, the latter being the distance from the star where it is cool enough for volatile icy compounds to remain solid. But Anne...

One of these days we're going to have a new generation of telescopes, some in space and some on the Earth, that can analyze the atmosphere of a terrestrial world around another star. It's not enough to find individual gases like oxygen and ozone, carbon dioxide or methane. Any of these can occur naturally without ramifications for life. But finding all of these gases in the same atmosphere is telling, because without life to replenish them, some would disappear. Getting the data is going to be hard, which is why new work using the European Southern Observatory's Very Large Telescope is so interesting. The work involves 'Earthshine,' the reflection of sunlight off the Earth that is in turn reflected off the surface of the Moon. It's faint, to be sure, but Earthshine is visible in a crescent Moon when the light of the entire lunar disc is visible although only the crescent is brightly lit. Michael Sterzik (ESO) and team have used Earthshine to analyze our own planet's biosignature, and...

I want to work a new paper on red dwarf habitability in here because it fits in so well with yesterday's discussion of the super-Earth GJ1214b. The latter orbits an M-dwarf in Ophiuchus that yields a hefty 1.4 percent transit depth, meaning scientists have a strong lightcurve to work with as they examine this potential 'waterworld.' In transit terms, red dwarfs, much smaller and cooler than the Sun, are compelling exoplanet hosts because any habitable worlds around them would orbit close to their star, making transits frequent. When I first wrote about red dwarfs and habitability in my Centauri Dreams book, it was in connection with the possibilities around Proxima Centauri, but of course we can extend the discussion to M-dwarfs anywhere, this being the most common type of star in the galaxy (leaving brown dwarfs out of the equation until we have a better idea of their prevalence). Manoj Joshi and Robert Haberle had published a paper in 1997 that described their simulations for...

I love the way Zachory Berta (Harvard-Smithsonian Center for Astrophysics) describes his studies of the transiting super-Earth GJ1214b. Referring to his team's analysis of the planet's atmosphere, Berta says "We're using Hubble to measure the infrared color of sunset on this world." And indeed they have done just this, discovering a spectrum that is featureless over a wide range of wavelengths, allowing them to deduce that the planet's atmosphere is thick and steamy. The conclusion most consistent with the data is a dense atmosphere of water vapor. Discovered in 2009 by the MEarth project, GJ1214b has a radius 2.7 times Earth's and a mass 6.5 times that of our planet. It's proven to be a great catch, because its host star, an M-dwarf in the constellation Ophiuchus, offers up a large 1.4 percent transit depth -- this refers to the fractional change in brightness as the planet transits its star. Transiting gas giants, for example, usually have transit depths somewhere around 1 percent,...

The dreams of Alpha Centauri I used to have as a boy all focused on visual effects. After all, the distance between Centauri A and B ranges from 11.4 to 36.0 AU. What would it be like to have a second star in our Solar System, one that occasionally closed to a little more than Saturn’s distance from the Sun? What would a day be like with two stars, and even more, what would night be like with a star that close lighting up the landscape? I also wondered about how much effect a second star would have on the planets in our system, curious as I was about gravitational effects and even the possible repercussions for weather and seasonal change. Image: The Alpha Centauri star system and other objects near it in the sky. Image copyright Akira Fujii / David Malin Images. You can imagine, then, that Duncan Forgan’s new paper hit close to home. Forgan (University of Edinburgh) has taken discussions of habitability around Centauri B to a new level by analyzing the effect of Centauri A on...

GJ 667C is an M-class dwarf, part of a triple star system some 22 light years from Earth. Hearing rumors that a 'super-Earth' -- and one in the habitable zone to boot -- has been detected around a nearby triple star system might cause the pulse to quicken, but this is not Alpha Centauri, about which we continue to await news from the three teams studying the prospect of planets there. Nonetheless, GJ 667C is fascinating in its own right, the M-dwarf being accompanied by a pair of orange K-class stars much lower in metal content than the Sun. The super-Earth that orbits the M-dwarf raises questions about theories of planet formation. Thus Steven Vogt (UC Santa Cruz), who puts the find into context, noting that heavy elements like iron, carbon and silicon are considered the building blocks of terrestrial planets: "This was expected to be a rather unlikely star to host planets. Yet there they are, around a very nearby, metal-poor example of the most common type of star in our galaxy....

I confess it had never occurred to me to consider cloud cover on exoplanets in quite the same light that a new study does. But two Spanish astronomers from the Astrophysical Institute of the Canary Islands (IAC) are taking a look at how clouds operate over different kinds of surfaces, in the process figuring out what our Earth would have looked like from space in different eras. It’s an interesting thought: Given the movement of Earth’s continents in the past 500 million years, what would cloud patterns have been like over land and sea as landforms changed? The researchers chose several times to study, from 90, 230, 340 to 500 million years ago, pondering how changes in light reflected from the Sun would have operated here and, by extension, how they might operate on distant exoplanets. We’ll need to keep these things in mind when we get the capability of studying the atmospheres of terrestrial planets around other stars. And it turns out that, according to the researchers, cloud...