Sara Seager often describes the distribution of exoplanets as 'stochastic,' meaning subject to statistical analysis but hard to predict. A good thing, then, that Kepler has given us so much statistical data to work with, allowing us to see the range of possible outcomes when stars coalesce and planetary systems emerge around them. We're not seeing copies of our own Solar System when we explore other stellar systems, but a variegated mix of outcomes. Thus finding a planet with an albedo as dark as fresh asphalt goes down as yet another curiosity from a universe that yields them in great abundance. The planet is WASP-12b, a 'hot Jupiter' of the most extreme kind. Previous work on this heavily studied world has already shown that due to its proximity to its host star, the planet has been stretched into an egg shape, while its day-side temperatures reach 2540 degrees Celsius, or 2810 Kelvin. 94 percent of incoming visible light here is trapped in an atmosphere so hot that clouds cannot...

You would think that seven planets around TRAPPIST-1 would be more than enough, but Alan Boss and colleagues at the Carnegie Institution for Science are asking whether this system might not also contain one or more gas giants. It's a theoretical question given weight by the desire to learn more about planet formation, for if we can find gas giants here, it would give credence to a model of gas giant formation championed by Boss. The team has now put constraints on the mass of any gas giants that might lurk here, a prelude to further study. The core accretion model is widely accepted as a way to create planets like our Earth. Here, the gas and dust disk surrounding a young star shows slow accretion as small particles begin to clump together, gradually forming into planetesimals and, via collisions and other interactions, eventually assembling planets, along with a great deal of leftover debris. Core accretion can be modeled and seems to fit what we see in other infant planetary...

We're going to need a lot more information about the effects of ultraviolet light as we begin assessing the possibility of life on the planets of red dwarf stars. We already know that young red dwarfs in particular can throw flares at UV wavelengths that can damage planetary atmospheres. They can also complicate our search for biosignatures through processes like the photodissociation of water vapor into hydrogen and oxygen, a non-biological source of oxygen of the kind we have to rule out before we can draw even tentative conclusions about life. Could flares have astrobiological benefits as well? That's a question that emerges from a new paper from Sukrit Ranjan (Harvard-Smithsonian Center for Astrophysics) and colleagues. What concerns Ranjan's team is that red dwarf stars may not emit enough ultraviolet to benefit early forms of life. On the primitive Earth, UV may have played a key role in the formation of ribonucleic acid. If this is the case, then UV flare activity could...

We're going to eventually get to know the seven planets of the TRAPPIST-1 system well. That's because they present the ideal targets for upcoming attempts to probe the atmospheres of Earth-sized rocky planets. Orbiting an M-dwarf some 39 light years out, all seven of the planets here transit. Because of the faintness of their star and the size of the planets themselves, they present excellent candidates for transit spectroscopy, in which we look at the light from the star through planetary atmospheres to deduce their constituents. Using the Space Telescope Imaging Spectrograph on the Hubble instrument, an international team led by Vincent Bourrier (Observatoire de l'Université de Genève) has been studying the ultraviolet radiation received by each of the planets in the system. The more we know about the star's output, the more we can plug values into the atmospheric escape processes that can occur in its planets, with huge consequences for surface conditions. The team in...

Looking at recent headlines about 'diamond rain' on Neptune provoked a few thoughts about headline writers, though the image is certainly striking, but then I recalled that Carl Sagan used to enjoy pulling out the stops with language as much as anyone. Listen, for example, to the beginning of his 1973 title The Cosmic Connection: There is a place with four suns in the sky -- red, white, blue and yellow; two of them are so close together that they touch, and star-stuff flows between them. I know of a world with a million moons. I know of a sun the size of the Earth - and made of diamond. There are atomic nuclei a mile across that rotate thirty times a second. There are tiny grains between the stars, with the size and atomic composition of bacteria. There are stars leaving the Milky Way. There are immense gas clouds falling into the Milky Way. There are turbulent plasmas writhing with X- and gamma rays and mighty stellar explosions. There are, perhaps, places outside our universe. And...

Whether or not life can emerge on the planets of red dwarf stars remains an unknown, though upcoming technologies should help us learn more through the study of planetary atmospheres. Tidal locking always comes up in such discussions, an issue I always thought to be fairly recent, but now I learn that it has quite a pedigree. In a new paper from Rory Barnes, I learn that astronomers in the late 19th Century had concluded (erroneously) that Venus was tidally locked, and there followed a debate about the impact of synchronous rotation on surface conditions. As witness astronomer N. W. Mumford, who in 1909 questioned whether tidal friction wouldn't reduce half of Venus to a desert and annihilate all life there. Or E. V. Heward, who speculated that life could emerge on Venus despite tidal lock, and wrote in a 1903 issue of MacMillan's Magazine: ...that between the two separate regions of perpetual night and day there must lie a wide zone of subdued rose-flushed twilight, where the...

I'm not much for changing the meaning of words. True, languages always change, some at a faster clip than others (contrast Elizabethan English with today's, though modern Icelandic is structurally very similar to the Old Norse of the sagas). But I love words and prefer to let linguistic variety evolve rather than be decreed. Even so, I get what Elizabeth Tasker is doing when she makes the case for exoplanet hunters to do away with the term 'habitable zone.' In a comment to Nature Astronomy, Tasker (JAXA) and quite a few colleagues point out just how misleading 'habitable zone' can be, given that when we find a new exoplanet, we usually only know the size of the planet (perhaps through radius, as in a transit study, or through minimum mass for radial velocity), and the amount of radiation the planet receives from its star. From such facts we can infer whether we're dealing with a gas giant or a rocky world. This is hardly enough on which to base a claim of habitability, but it gets...

The new work on Tau Ceti, which analyzes radial velocity data showing four planets there, looks to be a step forward in this workhouse method for planetary detection. With radial velocity, we're analyzing tiny variations in the movement of a star as it is affected by the planets around it. These are tiny signals, and the new Tau Ceti paper discusses working with variations as low as 30 centimeters per second. It's a good number, but we'll want better -- to detect a true Earth analog around a Sun-like star, we need to get this number into the 10 cm/s range. The planets detected in this work all come in at less than four Earth masses, and two of them are getting attention because they are located near the inner and outer edges of the habitable zone respectively. Tau Ceti has always drawn our attention, being relatively close (12 light years) and a solitary G-class Sun-like star. No wonder it and Epsilon Eridani were the two targets Frank Drake chose for Project Ozma when he launched...

If life can arise around red dwarf stars, you would think TRAPPIST-1 would be the place to look. Home to seven planets, this ultracool M8V dwarf star about 40 light years away in Aquarius has been around for a long time. The age range in a new study on the matter goes from 5.4 billion years up to almost ten billion years. And we have more than one habitable zone planet to look at. Adam Burgasser (UC-San Diego) and Eric Mamajek (JPL) are behind the age calculations, which appear in a paper that has been accepted at The Astrophysical Journal. We have no idea how long it takes life to emerge, having only one example to work with, but it's encouraging that we find evidence for it very early in Earth's history, dating back some 3.8 billion years. But we also have much to learn about habitability around red dwarfs in general. Image: This illustration shows what the TRAPPIST-1 system might look like from a vantage point near planet TRAPPIST-1f (at right). Credit: NASA/JPL-Caltech. [PG note...

We're beginning to find stratospheres on planets around other stars. A new study based at NASA Ames has looked closely at WASP-121b, a 'hot Jupiter' in its most extreme form. This is a planet about 1.2 times as massive as Jupiter, but with a radius almost twice Jupiter's. The puffy world orbits its star in a scant 1.3 days (Jupiter, by contrast, circles the Sun every twelve years). As you would imagine, temperatures on WASP-121b are extreme, reaching 2500 degrees Celsius, which is enough to cause some metals to boil. A stratosphere is simply a layer within an atmosphere where temperature increases with higher altitudes. Exactly how do scientists determine whether a planet fully 900 light years from Earth has such a layer? The answer is in the signature of hot water molecules, observed here by examining how these molecules in WASP-121b's atmosphere react to specific wavelengths of light. The researchers used spectroscopic data from the Hubble instrument to make the call, knowing that...

Frank Elmore Ross (1874-1960), an American astronomer and physicist, became the successor to E. E. Barnard at Yerkes Observatory. Barnard, of course, is the discoverer of the high proper motion of the star named after him, alerting us to its proximity. And as his successor, Ross would go on to catalog over 1000 stars with high proper motion, many of them nearby. Ross 128, now making news for what observers at the Arecibo Observatory are calling "broadband quasi-periodic non-polarized pulses with very strong dispersion-like features," is one of these, about 11 light years out in the direction of Virgo. Any nearby stars are of interest from the standpoint of exoplanet investigations, though thus far we've yet to discover any companions around Ross 128. An M4V dwarf, Ross 128 has about 15 percent of the Sun's mass. More significantly, it is an active flare star, capable of unpredictable changes in luminosity over short periods. Which leads me back to that unusual reception. The SETI...

‘Planetary mass binary’ is an unusual term, but one that seems to fit new observations of what was thought to be a brown dwarf or free-floating large Jupiter analog, and now turns out to be two objects, each of about 3.7 Jupiter masses. That puts them into planet-range when it comes to mass, as the International Astronomical Union normally considers objects below the minimum mass to fuse deuterium (13 Jupiter masses) to be planets. This is the lowest mass binary yet discovered. A team led by William Best (Institute for Astronomy, University of Hawaii) went to work on the L7 dwarf 2MASS J11193254–1137466 with the idea of determining what they assumed to be the single object’s mass and age. It was through observations with the Keck II telescope in Hawaii that they discovered the binary nature of their target. The separation between the two objects is about 3.9 AU, based upon the assumption that the binary is around 160 light years away, the distance of the grouping of stars called the...

Our theories of planet formation grow more mature as the exoplanet census continues, but I've always speculated about the first planets discovered and how they could have possibly been where we found them. The discovery of the planets around the pulsar PSR B1257+12 occurred in 1992, the work of the Polish astronomer Aleksander Wolszczan. Anomalies in its pulsation period -- this is a millisecond pulsar with a period of 6.22 milliseconds -- led Wolszczan and Dale Frail to produce a paper on the first extrasolar planets ever found. We wouldn't find such planets at all if it were not for the effect of their gravitational pull on the otherwise regular pulses from the pulsar. But how could the planets now know as Draugr, Poltergeist and Phobetor, the latter found in 1994, possibly have formed in such an environment? After all, a dense neutron star (a pulsar is a highly magnetized, rotating neutron star) is the result of a supernova that should have destroyed any planets nearby, making it...

Interesting news keeps coming out of the National Astronomy Meeting in the UK. Today it involves brown dwarfs and their distribution throughout the galaxy, a lively question given how recently we’ve begun to study these ‘failed stars.’ Maybe we need a better name than ‘brown dwarfs,’ for that matter, since these objects are low enough in mass that they cannot sustain stable hydrogen fusion in their core. In a murky intermediary zone between planet and star, they can produce planets of their own but straddle all our contemporary definitions. At the NAS meeting, an international team led by Koraljka Muzic (University of Lisbon) has reported on its work on brown dwarfs in clusters. It seems a sensible approach -- go to the places where young stars are forming and try to figure out how many brown dwarfs emerge alongside them. That could help to give us an overview, because the brown dwarfs we’ve already found (beginning with the first, in 1995) are generally within 1500 light years of...

The prospects for life around M-dwarf stars, always waxing and waning depending on current research, have dimmed again with the release of new work from Christina Kay (NASA GSFC) and colleagues. As presented at the National Astronomy Meeting at the University of Hull (UK), the study takes on the question of space weather and its effect on habitability. We know that strong solar flares can disrupt satellites and ground equipment right here on Earth. But habitable planets around M-dwarfs -- with liquid water on the surface -- must orbit far closer to their star than we do. Proxima Centauri b, for example, is roughly 0.05 AU from its small red host (7,500,000 km), while all seven of the TRAPPIST-1 planets orbit much closer than Mercury orbits the Sun. What, then, could significant flare activity do to such vulnerable worlds? Image: Artist’s impression of HD 189733b, showing the planet’s atmosphere being stripped by the radiation from its parent star. Credit: Ron Miller. Working with...

The European Space Agency has just announced the official adoption of the PLATO mission. The untangled acronym -- PLAnetary Transits and Oscillations of stars -- tells us that, like Kepler and CoRoT, this is a planet hunting mission with asteroseismological implications. Photometric monitoring of nearby bright stars for planetary transits and determination of planetary radii should help build our target list for spectroscopic follow-up as we delve into planetary atmospheres looking for biosignatures. Launch is scheduled for 2026. Asteroseismology studies how stars oscillate, giving us information about the internal structure of the star that would not be available through properties like brightness and surface temperature. PLATO will be carrying out high precision photometric monitoring at visible wavelengths, targeting bright stars (mV ? 11), though with capabilities for fainter stars down to magnitude 16. Several hundred thousand stars will ultimately be characterized in the search...

As announced yesterday at NASA Ames, the Kepler team has released the final Kepler catalog from the spacecraft’s first four years of data and its deep stare into Cygnus. The numbers still impress me despite our having watched them grow with each new report: We have 4034 planet candidates, of which 2335 have been verified as exoplanets. More than 30 of the approximately 50 near-Earth sized habitable zone candidates have been verified. The new release brought us 219 new candidates, 10 of them habitable zone possibilities, giving us a final catalog that is our first take on the prevalence and characteristics of planets in the Milky Way, and paving the way for future space-based instruments as we look for targets for atmospheric characterization and direct imaging. By introducing simulated planet transit signals and adding known false signals, the researchers were able to tighten up the catalog, ensuring against errors in the analysis growing out of the team’s processing methods. The...

The Pale Red Dot campaign that discovered Proxima Centauri b produced one of the great results of exoplanet detection. For many of us, the idea that a world of roughly Earth mass might be orbiting in Proxima Centauri's habitable zone -- where liquid water can exist on the surface -- was almost too good to be true, and it highlighted the real prospect that if we find such a planet around the closest star to our own, there must be many more around similar stars. Hence the importance of learning more about our closest neighbors. Which is why it's so heartening to see that Pale Red Dot is by no means done. This morning, the team led by Guillem Anglada-Escudé (Queen Mary University, London) announced plans to acquire data from the European Southern Observatory's HARPS instrument (High Accuracy Radial velocity Planet Searcher) in a new campaign to study not just Proxima Centauri in search of further planets, but also the red dwarfs Barnard's Star and Ross 154. Also involved will be...

Small stars are fascinating because of their sheer ubiquity. Some estimates for the fraction of red dwarfs in the galaxy go as high as 80 percent, meaning the planets around such stars are going to be the most common venues for possible life. For a time, I thought brown dwarfs would be shown to be even more numerous, but the WISE [Wide-field Infrared Survey Explorer] data have indicated otherwise (see Brown Dwarfs Sparser than Expected). Hopes for a brown dwarf closer than the Alpha Centauri stars (and thus a convenient intermediary destination for future probes) have dwindled down to nothing, but we do have interesting systems like Luhman 16 AB, the third closest system to the Sun, captured in the image below via a 'stack' of twelve images courtesy of the Hubble instrument. The work is from Luigi Bedin (INAF-Osservatorio Astronomico di Padova, Italy) and team, helping us with orbital parameters of the pair and demonstrating that there is no third companion. Image: Luhman 16 AB as...

Just how did the seven planets around TRAPPIST-1 form? This is a system with seven worlds each more or less the size of the Earth orbiting a small red dwarf. If these planets formed in situ, an unusually dense disk would have been required, making planet migration the more likely model. But if the planets migrated from beyond the snowline, how do we explain their predominantly rocky composition? And what mechanisms are at work in this system to produce seven planets all of approximately the same size? New work out of the University of Amsterdam attempts to resolve the question through a different take on planet formation, one that involves the migration not of planets but planetary building blocks in the form of millimeter to centimeter-sized particles. Chris Ormel (University of Amsterdam) and team note that thermal emission from pebbles like these has been observed around other low-mass stars and even brown dwarfs. The researchers believe these migrating particles become planetary...