With 250 times more X-ray radiation than Earth receives and high levels of ultraviolet, would Proxima b, that tantalizing, Earth-sized world around the nearest star, have any chance for habitability? The answer, according to Jack O’Malley-James and Lisa Kaltenegger (Cornell University) is yes, and in fact, the duo argue that life under these conditions could deploy a number of possible strategies for dealing with the radiation influx. Their conclusions appear in a new paper in Monthly Notices of the Royal Astronomical Society. Kaltenegger is director of Cornell’s Carl Sagan Institute, where O’Malley-James serves as a research associate. Modeling surface environments on four exoplanets that are prone to frequent flares -- Proxima-b, TRAPPIST-1e, Ross-128b and LHS-1140b -- Kaltenegger and O’Malley-James examined different atmospheric solutions that could suppress UV damage in living cells. Thin atmospheres and a lack of ozone protection fail to block UV radiation well, no surprise...

An iron and nickel-rich planetesimal is apparently all that survives of a planet following the death of its star, SDSS J122859.93+104032.9. We are talking about an object in an orbit around a white dwarf so tight that it completes a revolution every two hours. Significantly, spectroscopic methods were used to make the identification, the first time a solid body has been found around a white dwarf with spectroscopy. Variations in emitted light were used to identify the gases generated by the planetesimal, with data from the Gran Telescopio Canarias in La Palma. Lead author Christopher Manser (University of Warwick) notes the advantages of the method the team developed to study a white dwarf 400 light years away: "Our discovery is only the second solid planetesimal found in a tight orbit around a white dwarf, with the previous one found because debris passing in front of the star blocked some of its light -- that is the "transit method'' widely used to discover exoplanets around...

A method for enhanced exoplanet investigation takes center stage today as we look at the GRAVITY instrument, a near-infrared tool aided by adaptive optics that brings new precision to exoplanet imaging. In operation at the European Southern Observatory's Very Large Telescope Interferometer (VLTI) at Paranal Observatory in Chile, GRAVITY works with the combined light of multiple telescopes to produce what would otherwise take a single telescope with a mirror diameter of 100 meters to equal. The early demonstrator target is exoplanet HR 8799e. The method at work is interferometry, and here we are applying it to a ‘super Jupiter,’ more massive and much younger (at 30 million years) than any planet in our Solar System. The GRAVITY observations of this target mark the first time that optical interferometry has been used to study an exoplanet at this level of precision, producing a highly detailed spectrum. The planet is part of a 5-planet system some 130 light years away, all 5 of the...

Picking up on TESS (Transiting Exoplanet Survey Satellite), one of whose discoveries we examined yesterday, comes news of a document called the "TESS Habitable Zone Star Catalog." The work of Cornell astronomers in collaboration with colleagues at Lehigh and Vanderbilt, the paper has just been published in Astrophysical Journal Letters (citation below), where we find 1,822 stars where TESS may find rocky terrestrial planets. The listed 1,822 are nearby stars, bright, cool dwarfs, with temperatures roughly between 2,700 and 5,000 Kelvin, with a TESS magnitude brighter than 12 and reliable data from the Gaia Data Release 2 as to distance. Here TESS can detect 2 transits of planets that receive stellar irradiation similar to Earth's, during the 2-year prime mission. 408 of these stars would allow TESS to detect transiting planets down to Earth size during one transit. The catalog is fine-tuned to the TESS instrumentation and mission parameters, the stars selected because they offer...

It’s good to see TESS, the Transiting Exoplanet Survey Satellite, producing early results. We’re coming up on the one year anniversary of its launch last April 18, with the spacecraft’s four cameras doing month-long stares at 26 vertical strips of sky, beginning with the southern hemisphere. Two years of such scanning will produce coverage of 85 percent of the sky. The focus on bright, nearby stars is a shift from the Kepler strategy. While both missions have dealt with planetary transits across the face of their star as seen from the spacecraft, TESS is going to be producing plenty of data for follow-ups, planets close enough that we can consider studying their atmospheres with future missions beginning with the James Webb Space Telescope. Kepler’s long stare was of distant stars in a specific region, the idea being to gain a statistical understanding of the prevalence of planets. TESS gets us closer to home. Now we have TOI-197 (TOI stands for ‘TESS Object of Interest’), a planet...

Biosignature gases are those that can alert us to the possibility of life on a planet around another star. We're moving into the era of biosignature observation by studying the atmospheres of such planets through instruments like the James Webb Space Telescope, and the effort to catalog the combinations of atmospheric gases that point to life is intense and ongoing. One gas has turned out to be controversial. It's carbon monoxide, which in some quarters has been considered to be the opposite of a biosignature, a clear sign, if detected in sufficient abundance, that a planet is not inhabited. Edward Schwieterman (UC-Riverside) begs to disagree, and a team led by Schwieterman has produced its modeling of biosphere and atmosphere chemistry to focus on living planets that nonetheless support carbon monoxide at levels we should be able to detect. The work appears in the Astrophysical Journal. Interestingly, the paper harks back to our own planet's deep past. We don't expect to see high...

Kepler-62 is a reminder of how interesting K-class stars (like Alpha Centauri B) can be. Here we find two worlds that are conceivably in the habitable zone of their star, with Kepler 62f, imagined in the image below, orbiting the host star every 267 days. Kepler-62e, the bright object depicted to the right of the planet, may orbit within the inner edge of the habitable zone. Both planets are larger than Earth, Kepler 62f about 40 percent so, while Kepler-62e is 60 percent larger. Image: The artist's concept depicts Kepler-62f, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra. Credit: NASA Ames/JPL-Caltech/Tim Pyle. We actually have five planets here, all known thanks to Kepler to transit their star. The two of habitable zone interest may or may not be solid planets -- their masses are not well constrained through either radial velocity or transit timing methods, so we are a...

A planet designated Kepler-1658b is, after a good deal of investigation, demonstrated to be a 'hot Jupiter,' orbiting a star that is 50 percent more massive and three times larger than the Sun. The sizzling world is close enough to its star that were you to look into its sky from near the planet, the star would be 60 times larger than the Sun as seen from Earth. And while none of this makes Kepler-1658b unique in our catalog, what does stand out is how we learned all this. For we are talking about the first planet candidate ever uncovered with the Kepler Space Telescope. Recall that for any transiting planet to be considered confirmed, we need a second kind of detection. The reason: Various astrophysical processes can mimic transit activity. Prudence dictates the backup, and in the case of Kepler-1658b, both the initial estimate of the star's size and the size of the planet were underestimated. The result was that the putative world became thought of as a false positive whose numbers...

The sheer range of possible outcomes in a planetary system is something we’re beginning to appreciate with each new exoplanet. Not long ago we looked at a possible collision between two large worlds in the young system Kepler 107, and the knowledge of how violent an evolving system can be informs our thinking about the formation of our own Moon and other Solar System phenomena. Now we’re learning to look for signs of another kind of early cataclysm, the migration of a planet caused by the close passage of one or more nearby stars. None of this should be surprising when we think about the outer system today. We have a vast cloud made up of trillions of comets encircling a more disk-like belt of debris in the Kuiper Belt, and a host of small objects moving on orbits that challenge our theories of how they formed. Indeed, the orbits of ‘scattered disk’ objects influenced by Neptune and, even more intriguing, unusual trans-Neptunian objects like Sedna may implicate a yet undiscovered...

If you had a hot new instrument like the Habitable Zone Planet Finder (HPF) now mounted at the Hobby-Eberly Telescope (McDonald Observatory, University of Texas), how would you run it through its paces for fine-tuning and verification of its performance specs? The team behind HPF has chosen to deploy the instrument during its commissioning phase on a nearby target, Barnard's Star, which for these purposes we can consider something of an M-dwarf standard. Working at near-infrared wavelengths, HPF uses radial velocity methods to identify low-mass planets around nearby M-dwarf stars. The choice of wavelength is determined by the mission: M-dwarfs (also known as 'red dwarfs') are prey to substantial magnetic activity that shows up as spots and flares that disrupt instruments working in visible light, not to mention the fact that they are small to begin with and thus faint on the sky. In the near-infrared, close to but not in the visible spectrum, this category of star appears brighter...

It seems increasingly clear that the factors that govern what kind of a planet emerges where in a given stellar system are numerous and not always well understood. Beyond the snowline, planets draw themselves together from the ice and other volatiles available in these cold regions, so that we wind up with low-density gas or ice-giants in the outer parts of a stellar system. Sometimes. Rocky worlds are made of silicates and iron, elements that, unlike ice, can withstand the much warmer temperatures inside the snowline. But consider: While we now have 2,000 confirmed exoplanets smaller than three Earth radii, the spread in their densities is all over the map. We’re finding that other processes must be in play, and at no insubstantial level. Low-density giant planets can turn up orbiting close to their stars. Planets not so dissimilar from Earth in terms of their radius may be found with strikingly different densities in the same system, and at no great distance from each other. Which...

It's hard to fathom when we look at a globe, but our planet Earth's substantial covering of ocean is relatively modest. Alternative scenarios involving 'water worlds' include rocky planets whose silicate mantle is covered in a deep, global ocean, with no land in sight. Kilometer after kilometer of water covers a layer of ice on the ocean floor in these models, making it unlikely that the processes that sustain life here could develop -- how likely is a carbon cycle in such a scenario, and without it, how do we stabilize climate and make an inhabitable world? These are challenging issues as we build the catalog of exoplanets and try to figure out local conditions. But it's also intriguing to ask what made Earth turn out as dry as it is. Tim Lichtenberg developed a theory while doing his thesis at the Eidgenössische Technische Hochschule in Zürich (he is now at Oxford), and now presents it in a paper in collaboration with colleagues at Bayreuth and Bern, as well as the University of...

One of the joys of science fiction is imagining landscapes. What would it be like to stand on Titan, for example, a question that was inescapably influenced in my youth by Chesley Bonestell’s wonderful depictions, as well as novels like Larry Niven’s World of Ptavvs (1966) or Michael Swanwick’s novelette “Slow Life” (Analog, December 2002). And then, of course, there were those multi-star skies, as in Asimov’s “Nightfall” (Astounding Science Fiction September, 1941. The Science Fiction Writers of America, incidentally, voted “Nightfall” the best science fiction story written prior to 1965, when the Nebula Awards began. I would bet almost all Centauri Dreams readers are familiar with it, but if not, it’s widely anthologized. And now we have another visual phenomenon to contend with, a landscape and its sky that had never occurred to me. A team led by Grant Kennedy (University of Warwick, UK) has discovered the first confirmed case of a multiple star system whose surrounding disk of...

Barnard’s Star b, the planet announced last November around the second nearest star system to the Earth, has been the subject of intensive study by an international team led by Ignasi Ribas at the Institute of Space Studies of Catalonia (IEEC), and Institute of Space Sciences (ICE, CSIC). As announced at the recent meeting of the American Astronomical Society in Seattle, the work helps to refine the age of Barnard’s Star and examines its potential for supporting life on its known planet. We don’t know whether there are other planets around Barnard’s Star, but the fact of Barnard Star b’s existence is significant, according to Scott Engle (Villanova University), who along with colleague Edward Guinan presented the results in Seattle. Says Engle: “The most significant aspect of the discovery of Barnard’s Star b is that the two nearest star systems to the Sun are now known to host planets. This supports previous studies based on Kepler Mission data, inferring that planets can be very...

We can identify a number of circumstellar disks, but most are too far away to provide internal detail, much less the kind of activity that seems to be showing up around the red dwarf AU Microscopii. For at 32 light years out in the southern constellation Microscopium, AU Microscopii is presenting us with an unusual kind of activity that may have repercussions for the question of life around red dwarf stars in general. As presented at the recent meeting of the American Astronomical Society, fast-moving blobs of material are eroding the disk. The consequence: Icy materials and organics that might have developed in asteroids and comets may instead be pushed out of the disk, long before they could provide the infall of materials thought to have benefited planets like ours. "The Earth, we know, formed 'dry,' with a hot, molten surface, and accreted atmospheric water and other volatiles for hundreds of millions of years, being enriched by icy material from comets and asteroids transported...

We are entering the greatest era of discovery in human history, an age of exploration that the thousands of Kepler planets, both confirmed and candidate, only hint at. Today Ashley Baldwin looks at what lies ahead, in the form of several space-based observatories, including designs that can find and image Earth-class worlds in the habitable zones of their stars. A consultant psychiatrist at the 5 Boroughs Partnership NHS Trust (Warrington, UK), Dr. Baldwin is likewise an amateur astronomer of the first rank whose insights are shared with and appreciated by the professionals designing and building such instruments. As we push into atmospheric analysis of planets in nearby interstellar space, we'll use tools of exquisite precision shaped around the principles described here. by Ashley Baldwin This review is going to look at the current state of play with respect to direct exoplanet imaging. To date this has only been done from ground-based telescopes, limited by atmospheric turbulence...

Almost all the exoplanets we know have been detected in evolved stellar systems, places where the protoplanetary disk has dissipated and the planets around the star can be observed. Seeing inside a disk in formation is tricky business, though prominent studies at stars like Beta Pictoris have told us much about the evolution of these disks as planets do begin to emerge. But just how common are disks with ring and gap structures? Do all such disks produce planets? We're beginning to learn more as instruments like the Atacama Large Millimeter Array (ALMA) continue to be used to examine infant systems. Many of these show disks that are uniform in appearance, lacking discernible features like rings or gaps. Others are brighter, marked by concentric rings with separations that imply planet formation. It’s natural enough that early efforts have been devoted to brighter disks with their suggestion of planetary activity. Image: Until recently, protoplanetary disks were believed to be smooth,...

You would think that helium, being the second most common element in the universe, would have been detected in exoplanet atmospheres long ago. A major constituent of the atmosphere at both Jupiter and Saturn, helium seems a natural because planets form from dust and gas from previous stellar generations, but it turns out that the first helium detection on an exoplanet occurred only this year, in a study led by Jessica Spake (University of Exeter). The planet in question, WASP-107b, yielded its helium signature in data gathered by the Hubble Space Telescope, a detection that showed clear signs of a comet-like tail forming as the planet's atmosphere escaped. Note the space-based detection: It's significant because Earth's atmosphere is opaque to the ultraviolet light the atoms in such an eroding atmosphere absorb. Could we make this kind of fine-grained study from the surface of the Earth? It turns out there's a way: Helium in its long-lived metastable state (as compared to its ground...

We'd like to know a lot more than we do about how planets create magnetic fields. After all, a major motivation for exoplanet research (though hardly the only one) is to find out whether there is other life in the universe. A magnetic field can protect planetary atmospheres from the effects of the host star's stellar wind, a stream of charged particles that could disrupt life's formation. Planets in close orbits of a central star are going to be particularly vulnerable. But if protecting a planetary surface as well as keeping its atmosphere intact are powerful factors in understanding its evolution, learning more about planetary magnetic fields isn't going to be easy. Consider a new paper from François Soubiran (École Normale Supérieure, Lyon) and Burkhard Militzer (UC-Berkeley). They're digging into the question of magnetic fields on super-Earths, in this case planets up to three times the mass of our own world. The scientists believe that magnetic fields could emerge here,...

As the exoplanet hunt deepens, we're seeing how research efforts build upon each other, and how the findings of one investigation play into the planning for another. Kepler candidate planets, for example, have been confirmed using ground-based telescopes in radial velocity investigations, giving an independent check that the putative world is really there. TESS (Transiting Exoplanet Survey Satellite) will find planets that refine the target list for the James Webb Space Telescope, with extremely large telescope technology already in the wings. What we sometimes forget is that this collaborative effort has already built up a healthy momentum. Having maxed out Kepler (and K2 was an outstanding rehabilitation of a damaged spacecraft), the operations of TESS will focus on bright, nearby stars. The momentum of TESS and its contributions to the upcoming JWST should remind us that we then have the European Space Agency's CHEOPS (CHaracterising ExOPlanet Satellite) mission queuing up for...