Our fascination with Alpha Centauri doubtless propels at least some of the recent interest in binary star systems, as we ponder the chances for habitable worlds around the nearest stars. But given that the population of binary or multiple star systems in our galaxy is as high as it is (multiple systems are common, and about 50 percent of stars have binary companions), determining the factors that influence habitability in this environment has much broader significance. A new study out of the Georgia Institute of Technology has been looking at the issue by modeling an Earth twin in various binary scenarios. So how does Alpha Centauri fare? We can find habitable zones in the Centauri A/B system, and into these the researchers introduced a simulated Earth around Centauri B to examine its axis dynamics. They also investigate the dynamical evolution of planets within the habitable zone of either star, generalizing from these results to the larger binary star population. The issue to be...

While the majority of exoplanet-hosting stars discovered so far are single, we do have multiple star systems in various configurations with planetary companions. This is fertile ground for study, and not just because the nearest stellar system, Alpha Centauri, contains a tight binary pair that is being closely investigated for planets. The third star here is, of course, Proxima Centauri, around which we already know of the existence of a planet in the habitable zone. The much broader question is, how likely are multiple star systems to host planets? Tackling this question in a new study is Markus Mugrauer (Friedrich Schiller University, Jena), who has been investigating how the existence of multiple stars in a system affects the formation and development of planets. Mugrauer has been working with the second data release from the European Space Agency’s Gaia mission (made available in April of last year). This release contains data collected by Gaia during the first 22 months of its...

The question of habitability on planets around M-dwarfs is compelling, and has been a preoccupation of mine ever since I began working on Centauri Dreams. After all, these dim red stars make up perhaps 75 percent of the stars in the galaxy (percentages vary, but the preponderance of M-dwarfs is clear). The problems of tidal lock, keeping one side of a planet always facing its star, and the potentially extreme radiation environment around young, flaring M-dwarfs have fueled an active debate about whether life could ever emerge here. At Northwestern University, a team led by Howard Chen, in collaboration with researchers at the University of Colorado Boulder, NASA's Virtual Planet Laboratory and the Massachusetts Institute of Technology, is tackling the problem by combining 3D climate modeling with atmospheric chemistry. The paper on this work, in press at the Astrophysical Journal, examines how general circulation models (GCM) have been able to simulate the large-scale circulation and...

It's good to see the European Space Agency's ARIEL mission getting a bit more attention in the media. The Atmospheric Remote-sensing Infrared Exoplanet Large-survey was selected earlier this year as an ESA science mission, scheduled for launch in 2028. Here the goal is to cull a statistically large sample of exoplanets to examine their evolution in the context of their parent stars. Giovanna Tinetti (University College London) is principal investigator. I would urge seeing ARIEL in the context of a different kind of evolution, that being the gradual growth in our technologies as we continue getting closer to studying the atmospheres of terrestrial-class worlds. For while ARIEL cannot achieve this feat -- its focus is on exoplanets of Jupiter-mass down to super-Earths, all on close orbits, with temperatures greater than 320 Celsius -- it leverages the fact that high temperature atmospheres keep their various interesting molecules in continual circulation, rather than letting them sink...

We often think of Jupiter as a mitigating influence on asteroid or comet strikes in the inner system, its gravity changing the trajectories of potential impactors. That would make gas giants a powerful determinant of the survivability of Earth analogues, at least in terms of habitability. While we continue to investigate the question, it's interesting to consider the damage a gas giant on an elliptical orbit might do to habitable zone planets. Stephen Kane (UC-Riverside), working with Caltech astronomer Sarah Blunt, decided to find out what would happen if, in their modeling, they introduced an elliptical gas giant into the system of an Earth twin. You may remember Kane's work earlier this year combining radial velocity with direct imaging methods to find three gas giants that had been previously unobserved (citation below). The monitoring of ten target stars continues even as this new work is published. We're beginning to find more planets at ever larger distances from their stars...

The formation of planets like Neptune under the core accretion model involves a protoplanetary core that reaches around 10 Earth masses before beginning to pull in surrounding gas, the latter being a runaway process that quickly builds the atmosphere around the object. Core accretion is most efficient at doing this just outside the snow line, but if we want to understand and test the theory, we need to know a lot more about how planets are distributed in this region. And that’s a problem, because recent microlensing surveys have found that planets like Neptune are most abundant much more distant from their host stars. Outward migration can account for such worlds, but we know little about exoplanets that form at the snow line, which is where the condensation of ices can factor into the emergence of a new world. Is this just an artifact of our still evolving microlensing detection techniques? Perhaps, and exceptions to the rule can therefore be helpful. Recent work that began with a...

NASA collaborates with the German Aerospace Center (DLR) on one of our more interesting observatories. SOFIA, the Stratospheric Observatory for Infrared Astronomy, is a Boeing 747 aircraft that flies an infrared telescope with a 2.7 m diameter mirror. Located on the port side of the fuselage near the tail, the telescope houses a number of instruments for infrared astronomy at wavelengths from 1-655 micrometers (μm). One of these is FORCAST (Faint Object Infrared Camera for the SOFIA Telescope), which has now spotted an intriguing phenomenon, one that may be flagging a collision of two exoplanets. The stars in question form a double system called BD +20 307, some 300 light years from Earth. Note the age of this system, about one billion years, an important consideration in what follows. About ten years ago, observations from the Spitzer instrument as well as ground observatories produced evidence of warm debris here, whereas from age alone, we would have expected warm circumstellar...

I continue to be fascinated by small stars. My earliest passion for such involved red dwarfs, which appeared to make habitable planet possibilities that would be of great interest to science fiction authors, assuming such environments could survive tidal lock and stellar flaring. But white dwarfs have a weird seductiveness of their own, because we're learning how to extract from them information about planets that orbited them before being consumed. Thus a new paper out of UCLA, which focuses on an unusual way of determining the geochemistry of rocks from beyond our Solar System. We can do this because white dwarfs, the remnants of normal stars that have gone through their red giant phase and collapsed into objects about the size of the Earth, have strong gravitational pull. That means we would expect heavy elements like carbon, oxygen and nitrogen to vanish into their interiors, utterly out of view to our instruments. We should see little more than hydrogen and helium, making what...

The news of a gas giant of half Jupiter's mass around a small red dwarf, GJ 3512 b, continues to resonate. It goes to what has become a well enshrined controversy among those who follow planet formation models. While core accretion is widely accepted as a way of building planets, gravitational instability has remained an option. We are not talking about replacing one model with another, but rather saying that there may be various roads to planet formation among the gas giants. In any case, GJ 3512 b makes a strong case that we have much to learn. When I think about gravitational instability, I go back to the work of Alan Boss (Carnegie Institution for Science), as he has long investigated the concept. I learned about it from his papers and his subsequent book The Crowded Universe (Basic Books, 2009). Here's how Boss describes it there: Proponents of the top-down mechanism… envision clumps of gas and dust forming directly out of the planet-forming disk as a result of the...

The gas giant GJ 3512 b does not particularly stand out at first glance. About 30 light years from the Sun, it orbits its host star in 204 days, discovered by radial velocity methods by the CARMENES collaboration, which is all about finding planets around small stars. But look more deeply and you discover what makes this find provocative. GJ 3512 b turns out to be a gas giant with about half the mass of Jupiter, and small red dwarfs like this one aren’t supposed to host such worlds. In fact, GJ 3512 b is at least an order of magnitude more massive than what we would expect from current theoretical models, making it an interesting test case for planet formation. Core accretion models assume the gradual agglomeration of material in a circumstellar disk, with small bodies banging into each other and growing over time until their gravity is sufficient to draw in an atmosphere from the surrounding gas. This gas giant defies the model, evidently having formed directly from the disk through...

Ongoing in Geneva is the joint meeting of the European Planetary Science Congress and the Division for Planetary Sciences of the American Astronomical Society. We can abbreviate the whole thing as EPSC-DPS 2019, and you can read more about it here. We'll track several stories here as they develop, but I notice that the European Space Agency's ARIEL mission, which is slated to make the first large-scale survey of exoplanet atmospheres, has been supporting a Data Challenge involving removing noise from exoplanet observations. So let's start there. The slant here is training computers to filter out errors in collecting exoplanet data caused by starspots and by instrumentation, with two winners, James Dawson (Team SpaceMeerkat), and Vadim Borisov (Team major_tom), announced yesterday in Geneva. All told, 112 teams registered for the competition, a heartening number illustrative of the growing interest in computational statistics and machine learning among exoplanet researchers. The top...

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...