We haven't talked much in these pages about atmospheric pressure when it comes to characterizing exoplanets, but recent discussions of 'super-Earths' and thick, hydrogen/helium atmospheres have raised the issue. All but simultaneously came the news of a paper from Amit Misra (a University of Washington graduate student) and co-authors describing a new way of detecting atmospheric pressure on exoplanets. Misra's simulations of Earth's own atmospheric chemistry involved teasing out the signature of dimer molecules from light at various wavelengths. While a monomer is a molecule that may bind chemically to other molecules, a dimer is a chemical compound made up of two similar monomers bonded together. Misra's work is intriguing because the stability of water on a planet's surface depends not just on temperature but pressure -- the latter affects water's boiling point and sublimation. Estimating surface pressure thus becomes an indicator for potential habitability. The problem is that...

Whether or not they’re suitable for life, habitable zone ‘super-Earths’ are seeing increased scrutiny around M-class dwarf stars because the mass ratio of planet to star makes detection easier than around more massive stars. We need radial velocity surveys to help us here because planets on orbits longer than 200-300 days will definitely be out of Kepler’s reach. Moreover, while Kepler targets many K, G and F-class stars, M-dwarfs aren’t bright enough to show up in large numbers in its field of view, making occurrence rates around such stars problematic. A 2013 paper by Courtney Dressing and David Charbonneau (Harvard-Smithsonian Center for Astrophysics) found that the Kepler sample contains 3897 stars with estimated effective temperatures below 4000K. Out of these, 64 are planet candidate host stars, with 95 candidate planets orbiting them. The researchers deduced from their analysis that about 15 percent of all red dwarfs have an Earth-sized planet in the habitable zone. Ravi...

The Kepler announcements yesterday were greatly cheering to those of us fascinated with the sheer process of doing exoplanetology. The ‘verification by multiplicity’ technique propelled the statistical analysis that resulted in 715 newly verified worlds, and we have yet to turn it loose on two more years of Kepler data (check Hugh Osborn's excellent Lost in Transits site for more on the method). For those who focus primarily on habitable worlds, the results seemed a bit more sparse, with just four planets found in the habitable zone. And even where we find such, there are reasons to wonder whether a ‘super-Earth’ could actually sustain life. Apropos of this question, a team of researchers led by Helmut Lammer (Austrian Academy of Sciences) has just published the results of its modeling of planetary cores, looking at the rate of hydrogen capture and removal for cores between 0.1 and 5 times the mass of the Earth found in the habitable zone of a G-class star. Cores like these...

A planet like Kepler-296f is bound to get a lot of publicity. Orbiting a star half the Sun's size and only five percent as bright, this world, twice the size of the Earth, appears to orbit in the habitable zone, where liquid water could exist on its surface. We focus so much on the potential of life that the four planets announced yesterday (out of 715 newly verified worlds) inevitably get special treatment. And we learn that Kepler-296f exists in a system with four other planets, orbiting the star every thirty days. What we don't know is whether we're dealing with a small Neptune-class world surrounded by a thick hydrogen/helium atmosphere or a water world with a deep ocean. An interesting world, to be sure, but the real story in yesterday's announcements from the Kepler team has to do with the 'verification by multiplicity' technique used to validate the existence of so many planets in 305 star systems. One of the findings papers titled "Almost All of Kepler's Multiple Planet...

Strong evidence for water in the atmosphere of the hot Jupiter Tau Boötis b has turned up, thanks to work by Geoffrey Blake (Caltech) and graduate student Alexandra Lockwood. But what's intriguing about the find isn't the water -- we've found water vapor on other planets -- but the method of detection. Lockwood and Blake used a modified radial velocity technique that has previously been deployed to detect low mass ratio binary stars. A top-flight instrument like the Near Infrared Echelle Spectrograph (NIRSPEC) at the W. M. Keck Observatory in Hawaii can separate the planetary and stellar components spectroscopically to produce this result. Image: Simulated data showing the method used for detecting water vapor features around the hot Jupiter tau Boötis b. In this example, the planetary signal has been increased in strength by several orders of magnitude relative to the actual signal. The dotted lines show the blue- and red-shifts of the planetary and stellar lines in the data,...

CSIRO, the Commonwealth Scientific and Industrial Research Organisation in Australia, is announcing the detection of violent events around the pulsar PSR J0738-4042, some 37,000 light years from Earth in the constellation Puppis. This southern hemisphere constellation was originally part of a larger constellation called Argo Navis, depicting the ship made famous by the journey of Jason and the Argonauts. But Argo Navis was divided into three smaller constellations, leaving Puppis (The Stern) as something of a mythological fragment. Image: An artist's impression of an asteroid breaking up. Credit: NASA/JPL-Caltech. Whatever its origins, Puppis is also home, from our Earthly perspective, to a pulsar around which radiation and sleeting high energy particles are common. Ryan Shannon, a member of the CSIRO research team, has previously examined how an infalling asteroid from a violent disk around a pulsar might affect it, slowing the pulsar's spin rate and affecting the shape of the radio...

Following up on yesterday's post on Gaia, it seems a good time to discuss PLATO, the European Space Agency's planet hunting mission, which has just been selected for launch by ESA's Science Policy Committee. The agency's Cosmic Vision program has already selected the Euclid mission to study dark energy (launch in 2020) and Solar Orbiter, an interesting attempt to study the solar wind from less than fifty million kilometers. Solar Orbiter will surely return data we'll want to discuss here in terms of magsails, electric sails and other ways to harness a solar wind about which we have much to learn. Solar Orbiter's launch is the closest of the three, scheduled for 2017, with PLATO pegged for 2024, the launch to be from the European spaceport in Kourou (French Guiana) aboard a Soyuz booster. Note that date, because it's expected, as this BBC story notes, that the ground-based European Extremely Large Telescope (E-ELT) will be operational in Chile by 2024, a reminder that it should be...

The young star known as L1527 offers a spectacular view at infrared wavelengths, a result of the configuration of gas and dust around it. Have a look at the image below, taken by the Spitzer Space Telescope, where light from the star escapes through the opening provided by a bipolar gas flow, illuminating the gas to highlight a nebula in the shape of a butterfly. Earlier radio studies of this star have shown that L1527 is surrounded by a gas disk that, from our perspective, is seen edge-on. Now new radio observations are helping us characterize the gas itself. Image: An infrared image of the protostar L1527 taken by the Spitzer Space Telescope. Credit: J. Tobin/NASA/JPL-Caltech. It's an interesting investigation because the chemical changes inside a disk as it forms are little understood. Intense observational effort has gone into studying the physical structure of protoplanetary disks, but separating the young disk and the infalling envelope of gas and dust that gives rise to it is...

As we continue to learn more about brown dwarf atmospheres, the dwarf ULAS J222711-004547 catches the eye because of its unusually red appearance. What Frederico Marocco (University of Hertfordshire) and team have learned through observations with the Very Large Telescope in Chile is that a thick layer of clouds in the upper atmosphere is responsible for its tint. Marocco’s data analysis tells us we are seeing clouds made up of mineral dust. In this UH news release, he specifically mentions enstatite and corundum. The clouds are floating in a hot atmosphere of water vapor, methane and possible ammonia. This brown dwarf may turn out to be uncommonly helpful. Thus Avril Day-Jones, a colleague of Marocco’s at the University of Hertfordshire, who contributed to the analysis: "Being one of the reddest brown dwarfs ever observed, ULAS J222711-004547 makes an ideal target for multiple observations to understand how the weather is in such an extreme atmosphere. By studying the composition...

It was always a good bet that we'd get plenty of surprises as data from Kepler began to come in, but the odd world known as Kepler-413b really does stand out. The transit method seems made to order for a certain regularity -- Kepler looks at how the light from a given star dims when a planet passes in front of it as seen from Earth. Slight changes in these transits can help us detect other worlds in the system or, perhaps, help us make future discoveries of exomoons. But what happens when the transit is so erratic that both these scenarios can be ruled out? Veselin Kostov and team have exactly that situation on their hands. According to Kostov (Space Telescope Science Institute and Johns Hopkins University), the data for Kepler-413b show, over a period of 1500 days, three transits in the first 180 days, followed by 800 days with no transits at all. Following that, the researchers noted five more transits in a row. And according to their analysis, the next transit is not going to...

Learning that liquid water may exist beneath the surface of more than a few Solar System objects naturally raises astrobiological questions. But as Caleb Scharf notes in Water Erupts Across the Solar System, a much larger issue is whether the kind of chemoautotrophic microbes we find on Earth (Scharf calls them 'rock eaters') could have evolved there in the first place. Habitats that may support an Earth microbe aren't necessarily capable of originating their own forms of life, although the question is obviously going to propel much future study. What strikes me about a number of recent stories in these pages is how much what we see in our own and other solar systems may be the result of planetary migration, which can affect those water-bearing objects. Ceres is a case in point, and it was my reason for bringing up Caleb Scharf's always interesting blog in the first place. In Scharf's post, he takes note of the fact that Ceres is a bit too close to the Sun for comfort given its...

When I was growing up, Alpha Centauri was utterly dismissed as a possible location for planets. A binary system couldn't possibly produce them, I read, and it was assumed that planets could only be found around single stars like our own Sun. How times have changed. Now we know of plenty of multiple star systems with planets -- the number is over ten percent of all known exoplanets -- and while many of these are widely spaced, we've nonetheless found a few in tight circumstances indeed. HD196885 (Gamma Cephei) is an example, where the separation between the two stars is on the order of 20 AU, much like Centauri A and B. How planets form around such stars is an interesting issue because, as a new paper considering dust in the Alpha Centauri system explains, the standard core-accretion model runs into problems with environments as perturbed as these. We can see the results in existing observations: Radial velocity methods detect no planets more massive than 2.5 Jupiter masses inside 4...

Luhman 16AB (otherwise known as WISE J104915.57-531906) holds out quite an allure for those of us hoping to see future exploratory missions to nearby interstellar space. As recounted here in December (see Possible Planet in Nearby Brown Dwarf System), the European Southern Observatory's Henri Boffin has found that this brown dwarf pair is likely home to a previously undetected companion. Bear in mind that we know of no closer brown dwarf; indeed, Luhman 16AB is no more than 6.6 light years out, making it the third closest system to our Sun after Barnard's Star and, of course, Alpha Centauri. We know very little about this putative companion other than Boffin's estimate that its likely mass is between a few Jupiter masses and perhaps as many as 30, but the good news is that the high end of this mass range should offer us an object that can be detected by adaptive optics, given the size of the apparent separation. In any case, radial velocity methods should work nicely here as well,...

Friday's look at habitable zones, and the possibilities of life below the surface or in the atmosphere of an exoplanet, segues naturally into the fascinating notion of 'superhabitable' worlds. René Heller (McMaster University) and John Armstrong (Weber State University) ponder the possibilities in a recent paper for Astrobiology. What if, the scientists ask, our notions of habitability are too closely crafted to our own anthropocentric viewpoint? Could there be planets that are actually more habitable than the Earth? Should the Earth itself be considered, with respect to a broader view of biology, only marginally habitable? The question has important ramifications for how we approach the search for other habitable worlds. We study extremophilic life forms on Earth and question whether conditions even more bizarre than these could still produce life. But Heller and Armstrong reframe the issue: The word 'bizarre' is here to be understood from an anthropocentric point of view....

I'm a great believer in what I might call the 'conventional' habitable zone; i.e., a habitable zone defined by the possibility of liquid water on the surface. The definition is offered not to exclude exotic possibilities like micro-organisms floating in the clouds of Venus or aquatic life deep inside an ice-covered moon like Europa. Rather, it acknowledges that finding life is hard enough without losing our focus. In terms of exoplanets and feasible near-term study, a warm planet with liquid water -- the kind we live on -- would command our immediate attention. But as we look at much broader issues of how life forms, we may indeed learn that our kind of life is but one component of a vast continuum, as recent work out of the University of Aberdeen reminds us. In a new paper published in Planetary and Space Science, researchers tackle the question of life living deep underground. Now the habitable zone starts to broaden, because things get warmer as we go deep. We know of life here on...

Conventional models of planet formation involve core accretion, where dust grains accumulate into protoplanets whose subsequent collisions and interactions produce planets, or gravitational instability, involving a rapid collapse from dense disk debris into a planetary core. But how far from the parent star does planet formation occur? The more we learn about protoplanetary disks, the more questions individual systems pose, as illustrated by the discovery highlighted today. I'm looking at the image of a young star called HD 142527 in the constellation Lupus, some 450 light years from Earth. The T Tauri star, some five million years old, is thought to be of about two solar masses. A team of Japanese astronomers using observations from the Atacama Large Millimeter/submillimeter Array (ALMA) has found an asymmetric ring of dust that appears, based on the density of dust in the densest part of the ring, to be producing planets. A previously discovered inner disk is confirmed by this...

2500 light years from Earth in the constellation of Cancer lies Messier 67, an open star cluster that is now known to be home to at least three planets. The new worlds, found using the HARPS spectrograph on the European Southern Observatory's 3.6-meter instrument at La Silla, come as the result of an observation program covering 88 selected stars in the cluster over a period of six years. The finding is noteworthy because we have so few known planets in star clusters of any kind. Moreover, one of these planets orbits a truly Sun-like star. Image: This wide-field image of the sky around the old open star cluster Messier 67 was created from images forming part of the Digitized Sky Survey 2. The cluster appears as a rich grouping of stars at the centre of the picture. Credit: ESO/Digitized Sky Survey 2 / Acknowledgement: Davide De Martin. I'm cautious about calling anything 'Sun-like' given how loosely that term has been used over the years, but ESO astronomers say the cluster star...

"Weather on Other Worlds" is an observation program that uses the Spitzer Space Telescope to study brown dwarfs. So far 44 brown dwarfs have fallen under its purview as scientists try to get a read on the conditions found on these 'failed stars,' which are too cool to sustain hydrogen fusion at their core. The variation in brightness between cloud-free and cloudy regions on the brown dwarf gives us information about what researchers interpret as torrential storms, and it turns out that half of the brown dwarfs investigated show these variations. Given the chance nature of their orientation, this implies that most, if not all, brown dwarfs are wracked by high winds and violent lightning. The image below could have come off the cover of a 1950's copy of Astounding, though there it would have illustrated one of Poul Anderson's tales with Jupiter as a violent backdrop ("Call Me Joe" comes to mind). Brown dwarfs are, of course, a much more recent find, and in many ways a far more...

As the 223rd meeting of the American Astronomical Society continues in Washington, we're continuing to see activity on the subject of mini-Neptunes and 'super-Earths,' the latter often thought to be waterworlds. Given how fast our picture of planets in this domain is changing, I was intrigued to see that Nicolas Cowan (Northwestern University) and Dorian Abbot (University of Chicago) have come up with a model that allows a super-Earth with active plate tectonics to have abundant water in its mantle and oceans as well as exposed continents. If Cowan and Abbot are right, such worlds could feature a relatively stable climate even if the amount of water there is far higher than Earth. Focusing on the planetary mantle, the authors point to a deep water cycle that moves water between oceans and mantle, a movement made possible by plate tectonics. The Earth itself has a good deal of water in its mantle. The paper argues that the division of water between ocean and mantle is controlled by...

Yesterday's look at the exoplanet KOI-314c showed us a world with a mass equal to the Earth, but sixty percent larger than the Earth in diameter. This interesting planet may be an important one when it comes to studying exoplanet atmospheres, for KOI-314c is a transiting world and we can use transmission spectroscopy to analyze the light that passes through the atmosphere as the planet moves in front of and then behind its star. A space-based observatory like the James Webb Space Telescope should be able to tease useful information out of KOI-314c. But the American Astronomical Society meeting in Washington DC continues, and it's clear that the technique of studying transit timing variations (TTV) is coming into its own as a tool for exoplanet investigation. David Kipping and colleagues use TTV to look for exomoons, and it was during such a search that they discovered KOI-314c. But consider the other AAS news. At Northwestern University, Yoram Lithwick has been measuring the masses...