We're beginning to probe the atmospheres of planets other than gas giants, a step forward that the next generation of space- and ground-based instruments will only accelerate. This morning we have word that the habitable zone 'super-Earth' eight times as massive as Earth orbiting the star K2-18 has been found to have water vapor in its atmosphere, making it the only exoplanet known to have water as well as temperatures that could sustain that water as a liquid on the surface. This is also our first atmospheric detection of any kind for a planet orbiting in the habitable zone of its star. Angelos Tsiaras (University College London Centre for Space Exochemistry Data) is lead author on this work, which appears today in Nature Astronomy: "Finding water in a potentially habitable world other than Earth is incredibly exciting. K2-18b is not 'Earth 2.0' as it is significantly heavier and has a different atmospheric composition. However, it brings us closer to answering the fundamental...

Our thinking on how planetary systems form includes the accretion of rocky bodies within a disk surrounding a young star, and we're examining such disks in numerous systems, such as the well studied Beta Pictoris. But the idea of accretion leaves many issues unsettled, such as what happens when large rocky bodies collide in the violent endgame of system formation. The Earth evidently underwent such a collision, with our own Moon being the tangible result. Caltech postdoc Simon Lock has been working with Sarah Stewart (UC-Davis) to study how such giant impacts unfold, running simulations of early planetary materials whose collisions can form bodies with masses between 0.9 and 1.1 Earth masses. The energy involved in such impacts is thought to allow, in some cases, the two colliding bodies to form a 'synestia,' or a rotating torus of planetary materials that will later cool into one or more spherical planets. The synestia is, however, but one outcome out of many produced by these...

It shouldn’t surprise us that first discoveries can be extreme. Consider that the first main sequence exoplanets we detected were ‘hot Jupiters.’ Nobody expected these (unless you discount John Barnes and Buzz Aldrin in Encounter with Tiber, and Greg Matloff, who advised them -- see Probing Ultrahot Jupiters -- but a radial velocity detection is rendered far more likely if a large planet is orbiting close to its star. And so we got 51 Pegasi b, and soon, others in the hot Jupiter category. Incidentally, the Barnes & Aldrin novel was finished though not published when the discovery of 51 Pegasi b was made in 1995. Nice prediction! Hot Jupiters may not be all that common, but they show up in early radial velocity work. I could throw in the first exoplanets of another kind as well, these being planets around a pulsar. Who, as Isidor Rabi once said about muons, ordered that? Extreme objects that push hard enough on their environment to be flagged by our current instrumentation are of...

Radial velocity methods for detecting exoplanets keep improving. We've gone from the first main sequence star with a planet (51 Pegasi b) in 1995 to over 450 planets detected with RV, a technique that traces minute variations in starlight as a star nudges closer, then further from us as it is tugged by a planet. Radial velocity, then, sees gravitational effects while not directly observing the planet, which may in some cases be studied by its transits or direct imaging. Image: 51 Pegasi b, also called "Dimidium," was the first exoplanet discovered orbiting a star like our sun. This groundbreaking find in 1995 confirmed that planets around main sequence stars could exist elsewhere in the universe. Credit: NASA. Transit methods have accounted for more planets, but radial velocity techniques are increasingly robust and continue to provide breakthroughs. Consider this morning's news about HR 5183, which is now known to be orbited by a gas giant designated HR 5183 b. Astronomers at the...

We usually talk about habitability in binary form -- either a planet is habitable or it is not, defining the matter with a 'habitable zone' in which liquid water could exist on the surface. Earth is, of course, the gold standard, for we haven't detected life on any other world. But it is conceivable that there are planets where conditions are more clement than our own, as Stephanie Olson (University of Chicago) has recently pointed out. The work, presented at the just concluded Goldschmidt Geochemistry Congress in Barcelona, models circulatory patterns in oceans, some of which may support abundant life if they exist elsewhere. The emphasis here is not so much on surface ocean currents but upwelling water from deep below. Says Olson: "We have used an ocean circulation model to identify which planets will have the most efficient upwelling and thus offer particularly hospitable oceans. We found that higher atmospheric density, slower rotation rates, and the presence of continents all...

These days we have a keen interest in small red dwarf stars (M-dwarfs) not only because they're ideal for study, with deep transits of worlds in their habitable zones and the prospect of future analysis of their atmospheres, but also because they are so plentiful. Comprising perhaps 80 percent of all stars, they may well be home to the great majority of planets in the galaxy. And while they are common, they're also long-lived, so that life would have plenty of opportunity to develop. Now we have word of new work using both the Transiting Exoplanet Survey Satellite (TESS) and the Spitzer Space Telescope. TESS is, of course, a transit hunter, looking for the telltale dips in light from a parent star when a planet passes in front of it. The planet in question is LHS 3844b, about 48.6 light years out, and discovered by TESS in 2018. Follow-up observations in the infrared with Spitzer have detected light from the surface of this newly discovered world, allowing study of its atmosphere and...

The faint glow of a directly imaged planet will one day have much to tell us, once we've acquired equipment like the next generation of extremely large telescopes (ELTs), with their apertures measuring in the tens of meters. Discovering the makeup of planetary atmospheres is an obvious deep dive for biosignatures, but there is another. Biofluorescence, a kind of reflective glow from life under stress, could be detectable in some conditions at astronomical distances. New work on the matter is now available from Jack O'Malley-James and Lisa Kaltenegger, at Cornell University's Carl Sagan Institute. The duo have been on the trail of biofluorescence for some time now, and in fact their paper in Monthly Notices of the Royal Astronomical Society picks up on a 2018 foray into biosignatures involving the phenomenon (citation below). Here the question is detectability in the context of biofluorescence as a protective mechanism, an 'upshift' of damaging ultraviolet into longer, safer...

So much rides on the successful launch and deployment of the James Webb Space Telescope that I never want to take its capabilities for granted. But assuming that we do see JWST safely orbiting the L2 Lagrange point, the massive instrument will stay in alignment with Earth as it moves around the Sun. allowing its sunshield to protect it from sunlight and solar heating. Thus deployed, JWST may be able to give us information more quickly than we had thought possible about the intriguing system at TRAPPIST-1. In fact, according to new work out of the University of Washington's Virtual Planetary Laboratory, we might within a single year be able to detect the presence of atmospheres for all seven of the TRAPPIST-1 planets in 10 or fewer transits, if their atmospheres turn out to be cloud-free. Right now, we have no way of knowing whether any of these worlds have atmospheres at all. A thick, global cloud pattern like that of Venus would take longer, perhaps 30 transits, to detect, but is...

If it seemed amazing to me that 50 years had gone by since Apollo 11, it surprises me as well to realize that, on a much shorter scale, the Transiting Exoplanet Survey Satellite (TESS) has been at work for a full year. In a recent news release, NASA is calling this "the most comprehensive planet-hunting expedition ever undertaken," presumably a nod to the mission's broad sky coverage as opposed to the sharply confined field of view of the Kepler mission. Whereas Kepler took a 'long stare' at its starfield in Cygnus and Lyra, TESS keeps alternating what it sees, looking at a 24-by-96 degree section of sky for 27 days at a time. Moreover, TESS scientists are homing in on stars much closer to our Solar System. While Kepler was looking along the Orion arm of the galaxy at stars generally between 600 and 3,000 light years out (more distant stars were too faint to observe transit lightcurves), TESS puts the emphasis on stars closer than 300 light years, though with a similar method of...

Some confusion has arisen about a possible circumplanetary disk in the system PDS 70, which I wrote about recently (see Exoplanet Moons in Formation?, from June 7). A team led by led by Valentin Christiaens at Monash (Australia) presented evidence for the kind of disk that may have formed the moons of Jupiter around the forming planet PDS 70b, using data from the Very Large Telescope, finding evidence for both the disk and a developing atmosphere here. The finding was admittedly tentative, which should be kept in mind as we resolve the discrepancy between this and a separate observation, what Rice University is calling in a news release 'the first observations of a circumplanetary disk of gas and dust…' What we have in the Rice document is a report on a paper from the university's Andrea Isella and colleagues, who studied millimeter wave radio signals from the Atacama Large Millimeter/submillimeter Array (ALMA) to identify a circumplanetary disk around the other forming planet...

We should always be on the lookout for new ways of finding exoplanets. Right now we're limited by our methods to stars within the neighborhood of the Sun (in galactic terms), for both radial velocity and transit detections are possible only around brighter, closer stars. The exception here is gravitational microlensing, capable of probing deep into the galaxy, but here the problem is one of numbers. We simply don't make enough detections this way to build up the kind of statistical sample that the Kepler mission has provided in terms of transiting planets. So how significant is this kind of selection bias, which thus far has been forced upon us? Without knowing the answer, we would do well to explore ideas like those put forward by Nicola Tamanini (AEI Potsdam) and colleague Camilla Danielski (CEA/Saclay, Paris). The two scientists are looking at the possibilities of gravitational wave astronomy, looking toward the launch, in the 2030s, of LISA, the Laser Interferometer Space...

We refine our terminology as we go when a field as new as exoplanetology is in play. Take the case of GJ 3470b. At 12.6 Earth masses, is this a 'sub-Neptune' or a 'super Earth'? Neptune itself is 17 Earth masses, so I'd on balance give the nod to 'sub-Neptune,' though categories here get confusing. The planet is 0.031 AU out from its star, a red dwarf half the mass of our Sun. Oddly, it has a hydrogen/helium atmosphere in which heavier elements are all but absent. We know this because scientists have been able to put data from both the Hubble instrument and Spitzer to work on an analysis of the atmosphere of the planet. This is done through a technique we've examined before, transmission spectroscopy, in which astronomers study the absorption of the star's light as the planet passes across its face (a transit as seen from Earth), and then the loss of reflected planetary light as the planet moves behind the star (this is called a secondary eclipse). Image: A comparison between...

The latest find from TESS, the Transiting Exoplanet Survey Satellite, is a reminder of how interesting, and useful, a planetary system can be even if we find no Earth-like worlds there. This seems obvious, but so much of the public attention to exoplanets has to do with finding a clone of our own world that we can forget the power of a 'second Jupiter' or, in this case, a 'second Venus.' For at L 98-59 we have not one but three planets that may fit this description. One Venus, hellish as it is, would seem to be enough. But learning about planets with varying kinds of atmospheres that are in orbits that produce runaway greenhouse effects can help us place our own system's evolution in context. To be sure, we don't yet know what kind of atmospheres these planets have, or if they have atmospheres at all, but the encouraging thing is that tight orbits around relatively bright stars are what we need as we look toward future tools like the James Webb Space Telescope. Astrophysicist Joshua...

We rarely talk about Teegarden's Star when mentioning interesting objects near the Solar System, probably because the star was only discovered in 2003 and until now had not been known to host planets. Today we learn, however, that an international team led by the University of Göttingen has found two planets close to Earth mass in what it considers to be the habitable zone around the tiny star. Interestingly, from where the system is located, any local astronomers would be able to see the planets of our Solar System in transit across the face of the Sun, about which more in a moment. One of the reasons that this comparatively nearby star has been so late to be discovered is its size. We are dealing with an M-class red dwarf, this one in the constellation Aries, and no more than 12.5 light years from us. It took three years of patient radial velocity monitoring to track down planets around a star that is only about 2700 degrees Celsius in temperature, and fully 10 times lighter than...

We’re getting first results from the Gemini Planet Imager Exoplanet Survey (GPIES), a four-year look at 531 young, nearby stars that relies on the instrument’s capabilities at direct imaging. Data from the first 300 stars have been published in The Astronomical Journal, representing the most sensitive, and certainly the largest direct imaging survey for giant planets yet attempted. The results of the statistical analysis are telling: They suggest that planets slightly more massive than Jupiter in outer orbits around stars the size of the Sun are rare. The Gemini Planet Imager (GPI), located at the Gemini South Telescope in Chile, can achieve high contrast at small angular separations, making it possible to see exoplanets directly, as opposed to the indirect methods that have dominated the field, such as transits and radial velocity analysis. As successful as the latter have been, they are most effective with planets closer to their stars, whereas an instrument like the GPI can find...

We're on the cusp of exciting developments in exoplanet detection, as yesterday's post about the Near Earths in the AlphaCen Region (NEAR) effort makes clear. Adapting and extending the VISIR instrument at the European Southern Observatory's Very Large Telescope in Chile, NEAR has seen first light and wrapped up its first observing run of Centauri A and B. What it finds should have interesting ramifications, for its infrared detection capabilities won't find anything smaller than twice the size of Earth, meaning a habitable zone discovery might rule out a smaller, more Earth-like world, while a null result leaves that possibility open. The NEAR effort relies on a coronagraph that screens out as much as possible of the light of individual stars while looking for the thermal signature of a planet. An internal coronagraph is one way to block out starlight (the upcoming WFIRST -- Wide Field Infrared Survey Telescope -- mission will carry a coronagraph within the telescope), but starshade...

I marvel that so many of the big questions that have preoccupied me during my life are starting to yield answers. Getting New Horizons to Pluto was certainly part of that process, as a mysterious world began to reveal its secrets. But we're also moving on the Alpha Centauri question. We have a habitable zone planet around Proxima, and we're closing on the orbital space around Centauri A and B, a G-class star like our Sun and a cooler K-class orange dwarf in a tight binary orbit, the nearest stars to our own. At the heart of the research is an instrument called a thermal infrared coronagraph, built in collaboration between the European Southern Observatory and Breakthrough Watch, the privately funded attempt to find and characterize rocky planets around not just Alpha Centauri but other stars within a 20 light year radius of Earth. The coronagraph blocks out most of the stellar light while being optimized to capture the infrared frequencies emitted by an orbiting planet. Note that...

We've been looking at circumstellar disks for quite some time, and teasing out images of actual planets within them, as witness HR 8799, where four exoplanets have been found. Just recently we saw imagery of a second world around PDS 70, both planets seen by direct imaging as they plowed through the disk of dust and gas surrounding a young star. All told, we now have more than a dozen exoplanets that have been directly imaged, though only two are in multi-planet systems. PDS 70b is sweeping out an observable gap in the disk. Image: PDS 70 is only the second multi-planet system to be directly imaged. Through a combination of adaptive optics and data processing, astronomers were able to cancel out the light from the central star (marked by a white star) to reveal two orbiting exoplanets. PDS 70 b (lower left) weighs 4 to 17 times as much as Jupiter while PDS 70 c (upper right) weighs 1 to 10 times as much as Jupiter. Credit: ESO and S. Haffert (Leiden Observatory). Now we learn that...

The Moon’s farside used to be a convenient setting for wondrous things. After all, no one had ever seen it, setting the imagination free to insert everything from paradisaical getaways (think Shangri-La in space) to secret technologies or alien civilizations. The Soviet Luna 3 image of 1959 took the bloom off that particular rose, but we also learned through this and subsequent missions that farside really does have its differences from the familiar face we see. More craters, for one thing, and fewer of the dark plains we call maria, or ‘seas.’ We can throw in measurements made by the GRAIL mission (the Gravity Recovery and Interior Laboratory) in 2012. GRAIL was a NASA Discovery-class mission that performed gravitational field mapping of the Moon as a way of examining its internal structure, a set of two probes that worked by analyzing measured changes in distance between the two craft as small as one micron. We wound up with a map of our satellite’s gravitational field that led to...

We should be glad to run into the unexpected when doing research, because things we hadn't foreseen often point to new understanding. That's certainly the case with infant planetary systems as observed through the circumstellar disks of gas and dust surrounding young stars. ALMA (the Atacama Large Millimeter/submillimeter Array) has been central to the study of such targets. An array of 66 radio telescopes in Chile's Atacama Desert, the facility works at millimeter and submillimeter wavelengths to provide detailed imaging of emerging systems. Because it has been revealing a variety of small-scale structures within circumstellar disks, ALMA is giving us insights into planet formation as we observe gaps, rings and spiral arms and their interactions with young planets. This is where the unexpected comes in. For researchers looking at a 5 million year old star called HD 163296 are seeing an unusual amount of dust, more than 300 times the mass of the Earth, despite the detection of at...