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...

A planet labeled NGTS-4b has turned up in a data space where astronomers had not expected it, the so-called ‘Neptunian desert.’ Three times Earth radius and about 20 percent smaller than Neptune, the world was discovered with data from the Next-Generation Transit Survey (NGTS), which specializes in transiting worlds around bright stars, by researchers from the University of Warwick. It turns out to be a scorcher, with temperatures in the range of 1,000 degrees Celsius. NGTS-4b is 20 times as massive as the Earth, and its orbit takes it around its star, a K-dwarf 920 light years out, every 1.3 days. The planet is getting attention not so much because of what it is but where it is. Lead author Richard West (University of Warwick) comments: "This planet must be tough - it is right in the zone where we expected Neptune-sized planets could not survive. It is truly remarkable that we found a transiting planet via a star dimming by less than 0.2% - this has never been done before by...

I’m always interested in hearing about new ways to mine our abundant datasets. Who knows how many planets may yet turn up in the original Kepler and K2 data, once we’ve applied different algorithms crafted to tease out their evanescent signatures. On the broader front, who knows how long we’ll be making new discoveries with the Cassini data, gathered in such spectacular fashion over its run of orbital operations around Saturn. And we can anticipate that, locked up in archival materials from our great observatories, various discoveries still lurk. Assuming, of course, we know how to find them and, just as important, how to confirm that we’re not just looking at noise. What scientists at the Max Planck Institute for Solar System Research (MPS), the Georg August University of Göttingen, and the Sonneberg Observatory have come up with is 18 new planets roughly of Earth size that they’ve dug out of K2, looking at 517 stars that, on the basis of earlier analysis, had already been...

In a white paper submitted to the Decadal Survey on Astronomy and Astrophysics (Astro2020), Philip Horzempa (LeMoyne College) suggests using technology originally developed for the NASA Space Interferometry Mission (SIM), along with subsequent advances, in a mission designed to exploit astrometry as an exoplanet detection mode. I'm homing in on astrometry itself in this post rather than the mission concept, for the technique may be coming into its own as an exoplanet detection method, and I'm interested in new ways to exploit it. Astrometry is all about refining our measurement of a star's position in the sky. When I talk to people about detecting exoplanets, I find that many confuse astrometry with radial velocity, for in loose explanatory terminology, both refer to measuring the 'wobble' a planet induces on a star. But radial velocity examines Doppler effects in a star's spectrum as the star moves toward and then away from us, while astrometry looks for tiny changes in the position...

The term 'destruction radius' around a star sounds like something out of a generic science fiction movie, probably one with lots of laser battles and starship crews dressed in capes. It's a descriptive phrase as used in this University of Warwick (UK) news release, but let's go with 'Roche radius' instead. Dimitri Veras, a physicist at the university, probes the term in the context of white dwarfs in a new paper for Monthly Notices of the Royal Astronomical Society. Veras and collaborators are looking at what happens after the challenging transition between red giant and white dwarf, a time when planets will be in high turmoil. The idea is to model the tidal forces that occur once a star collapses into a super-dense white dwarf, blowing away its outer layers in the process. We see the clear potential for dragging planets into new orbits, with some pushed out of their stellar systems entirely. The Roche radius, or limit, is the distance from the star where a self-gravitating object...

Interdisciplinary approaches to new data offer a robust way to see past the conventions of a specialized field, noting connections that provide perspective and deepen understanding. That idea is sound across many disciplines, but it is getting new emphasis with an essay in Science asking whether we have not been too blinkered in our approach to astrobiology. After all, reams have been written about studying exoplanet atmospheres for biomarkers, but shouldn't we be studying how atmospheres couple to planetary interiors? "We need a better understanding of how a planet's composition and interior influence its habitability, starting with Earth," says Anat Shahar (Carnegie Institution for Science), one of the paper's four authors. "This can be used to guide the search for exoplanets and star systems where life could thrive, signatures of which could be detected by telescopes." Thus the paper's call for merging data from astronomical observations, mathematical modeling and simulations, and...

If Kepler's task was to give us a first statistical cut at the distribution of exoplanets in the galaxy, TESS (Transiting Exoplanet Survey Satellite) has a significantly different brief, to use its four cameras to study stars that are near and bright. Among these we may hope to find the first small, rocky planets close enough that their atmospheres may be examined by space telescopes and the coming generation of extremely large telescopes (ELTs) on Earth. Thus the news that TESS has found its first planet of Earth size is heartening, even if the newly found world orbiting HD 21749 is in a tight 7.8 day orbit, making it anything but clement for life. What counts, of course, is the demonstrated ability of this mission to locate the small worlds we had hoped to find. Diana Dragomir is a postdoc at MIT's Kavli Institute for Astrophysics and Space Research, as well as lead author on the paper describing the latest TESS planet: "Because TESS monitors stars that are much closer and...

The transit method has proven invaluable for exoplanet detection, as the runaway success of the Kepler/K2 mission demonstrates. But stars where planets have been detected with this method are still capable of revealing further secrets. Consider Kepler-47. Here we have a circumbinary system some 3340 light years away in the direction of the constellation Cygnus, and as we are now learning about circumbinaries -- planets that orbit two stars -- the alignment of the orbital plane of the planet is likely to change with time. Let's pause for a moment on the value of the detection method. Transits detected in the lightcurve have helped us identify 10 transiting circumbinary planets, with the benefit of allowing astronomers to measure the planets' radius even as variations in the duration of transits and deviations from the expected timing of the transits establish the circumbinary orbit. At Kepler-47, we're looking at the only known multi-planet circumbinary system. Moreover, the orbital...

Seven planets of roughly Earth-size make TRAPPIST-1 a continuing speculative delight, as witness the colorful art it generates below. And with three of the planets arguably in the star's habitable zone, this diminutive star attracts the attention of astrobiologists anxious to examine the possible parameters under which they orbit. One thing that is only now receiving attention is the question of planet-to-planet tidal effects, as opposed to the star's tidal effects on its planets. Image: An artist's impression of the perpetual sunrise that might greet visitors on the surface of planet TRAPPIST-1f. If the planet is tidally locked, the "terminator region" dividing the night side and day side of the planet could be a place where life might take hold, even if the day side is bombarded by energetic protons. In this image, TRAPPIST-1e can be seen as a crescent in the upper left of the image, d is the middle crescent, and c is a bright dot next to the star. Credit: NASA/JPL-Caltech. In our...

A possible second planet around Proxima Centauri raises all kind of questions. I wasn't able to make it to Breakthrough Discuss this year, but I've gone over the presentation made by Mario Damasso of Turin Observatory and Fabio Del Sordo of the University of Crete, recounting their excellent radial velocity analysis of the star. Proxima c is a fascinating world, if it's there, because it would be a super-Earth in a distant (and cold) 1.5 AU orbit of a dim red star. Exactly how it formed and whether it migrated to its current position could occupy us for a long time. But is it there? The first difficulty has to do with stellar activity, which Damasso and Del Sordo were careful to screen out; it's one of the major problem areas for radial velocity work in this kind of environment, for red dwarf stars are often quite active. During the question and answer session, another key question emerged: We know from Kepler that many stars are orbited by multiple planets, and there is no reason to...

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...