The other day I looked at how we can use transit spectroscopy to study the atmospheres of exoplanets. Consider this a matter of eclipses, the first occurring when the planet moves in front of its star as seen from Earth. We can measure the size of the planet and also see light from the star as it moves through the planetary atmosphere, giving us information about its composition. The secondary eclipse, when the planet disappears behind the star, is also quite useful. Here, we can study the atmosphere in terms of its thermal variations. In my recent post, I used a diagram from Sara Seager to show primary and secondary eclipse in relation to a host star. The image below, by Josh Winn, is useful because it drills down into the specifics. Image: A comparison between transits and secondary eclipses (also sometimes called occultations). In a planetary transit, the planet crosses in front of the star (see lower dip) blocking a fraction of the star's brightness. In a secondary eclipse, the...

The Next Generation Transit Survey has come up with an interesting catch. A gas giant close to the size of Jupiter (about 20 percent less massive) has turned up orbiting a red dwarf some 600 light years away, with an orbital period of 2.6 days. With a temperature calculated at 800 Kelvin, NGTS-1b stands out not because it is a 'hot Jupiter' but because stars as small as this one are not normally associated with gas giants. The new planet is, in fact, the largest planet -- compared to the size of its companion star -- ever discovered. Image: Artist's impression of planet NGTS-1b with its neighbouring star. Credit: University of Warwick/Mark Garlick. The Next Generation Planet Survey is a wide-field photometric survey designed to find transiting exoplanets of Neptune-class and smaller around bright stars, using an array of fully-robotic small telescopes operating in the 600-900nm band. The survey is thus sensitive to K and early-M class stars, the goal being to provide targets for...

How likely are we to find a definitive biosignature once we begin analyzing the atmospheres of nearby rocky exoplanets? We have some ideal candidates, after all, with stars like TRAPPIST-1 yielding not one but three potentially life-bearing worlds. The first thing we'll have to find out is whether any of these planets actually have atmospheres, and what their composition may be. 'Habitable zone' is a fluid concept, and that's not just a reference to liquid water on the surface. A relatively dry terrestrial planet, one with little surface water and not a lot of water vapor in the atmosphere, might avoid a runaway greenhouse and manage to stay habitable in an orbit closer to a G-class star than Earth. A planet with an atmosphere dominated by hydrogen could maintain warm temperatures even at 10 AU and beyond. So we'll need to find out what any exoplanet atmosphere is made of, and weigh that against its orbital position near its star. Image: An extended habitable zone that captures some...

Video presentations from the recent Tennessee Valley Interstellar Workshop are beginning to appear online. It's welcome news for those of us who believe all conferences should be available this way, and a chance for Centauri Dreams readers to home in on particular presentations of interest. I published my Closing Remarks at TVIW right after the meeting and will watch with interest as the complete 2017 videos now become available. There are a number of these I'd like to see again. All of this gets me by round-about way to Project Blue, the ongoing attempt to construct a small space telescope capable of directly imaging an Earth-like planet around Centauri A or B, if one is indeed there. For the other talk I gave at TVIW 2017 (not yet online) had to do with biosignatures, and the question of whether we had the capability of detecting one in the near future with the kind of missions now approved and being prepared for launch. This was delivered as part of a presentation and panel...

An object called A/2017 U1, whether it is an asteroid or a comet, is drawing attention because it seems to be an interstellar wanderer. Discovered on October 19 by the University of Hawaii's Pan-STARRS 1 telescope on Haleakala, the object was quickly submitted to the Minor Planet Center by Rob Weryk (University of Hawaii Institute for Astronomy, IFA). Weryk was subsequently able to identify the object in Pan-STARRS imagery from the previous night. Image: This animation shows the path of A/2017 U1, which is an asteroid -- or perhaps a comet -- as it passed through our inner solar system in September and October 2017. From analysis of its motion, scientists calculate that it probably originated from outside our Solar System. Credit: NASA/JPL-Caltech. Thus a nightly search for near-Earth objects may have uncovered an object whose origins lie much further away. A/2017 U1 is about 400 meters in diameter and on a highly unusual trajectory, one that fits neither an asteroid or comet from...

Just how do you go about building a 'super-Earth'? One possibility may be emerging in the study of young debris disk systems with thin, bright outer rings made up of comet-like bodies. Three examples are under scrutiny in work discussed at the recent American Astronomical Society's Division for Planetary Sciences meeting in Provo, Utah. Here, Carey Lisse (JHU/APL) described his team's results in studying the stars Fomalhaut, HD 32297 and HR 4796A. What the scientists are finding is that dense rings of comets can become a construction zone for planets of super-Earth size. The makeup of the material in these ring systems varies, from two that are rich in ice (Fomalhaut and HD 32297) to one that is depleted in ice but rich in carbon (HR 4796A). Take a look at the image below, showing the ring surrounding HR 4796A, and you'll see how strikingly tight the band of dust around this relatively young stellar system is. Image: Gemini Planet Imager observations reveal a complex pattern of...

Eduardo Bendek's ACEsat, conceived at NASA Ames by Bendek and Ruslan Belikov, seemed to change the paradigm for planet discovery around the nearest stellar system. The beauty of Alpha Centauri is that the two primary stars present large habitable zones as seen from Earth, simply because the system is so close to us. The downside, in terms of G-class Centauri A and K-class Centauri B, is that their binary nature makes filtering out starlight a major challenge. Image: The Alpha Centauri system. The combined light of Centauri A (G-class) and Centauri B (K-class) appears here as a single overwhelmingly bright 'star.' Proxima Centauri can be seen circled at bottom right. Credit: European Southern Observatory. If we attack the problem from the ground, ever bigger instruments seem called for, like the European Southern Observatory's Very Large Telescope in conjunction with the VISIR instrument (VLT Imager and Spectrometer for mid-Infrared) that Breakthrough Initiatives is now working with...

Comparative exoplanetology? That's the striking term that Angelos Tsiaras, lead author of a new paper on exoplanet atmospheres, uses to describe the field today. Kepler's valuable statistical look at a crowded starfield has given us insights into the sheer range of outcomes around other stars, but we're already moving into the next phase, studying planetary atmospheres. And as the Tsiaras paper shows, constructing the first atmospheric surveys. Tsiaras (University College, London) assembled a team of European researchers that examined 30 exoplanets, constructing their spectral profiles and analyzing them to uncover the characteristic signatures of the gases present. The study found atmospheres around 16 'hot Jupiters,' learning that water vapor was present in each of them. Says Tsiaras: "More than 3,000 exoplanets have been discovered but, so far, we've studied their atmospheres largely on an individual, case-by-case basis. Here, we've developed tools to assess the significance of...

When we think about the markers of possible life on other worlds, vegetation comes to mind in an interesting way. We’d like to use transit spectroscopy to see biosignatures, gases that have built up in the atmosphere because of ongoing biological activity. But plants using photosynthesis offer us an additional option. They absorb sunlight from the visible part of the spectrum, but not longer-wavelength infrared light. The latter they simply reflect. What we wind up with is a possible observable for a directly imaged planet, for if you plot the intensity of light against wavelength, you will find a marked drop known as the ‘red edge.’ It shows up when going from longer infrared wavelengths into the visible light region. The red-edge position for Earth’s vegetation is fixed at around 700–760?nm. What we’d like to do is find a way to turn this knowledge into a practical result while looking at exoplanets. Where would we find the red edge on planets circling stars of a different class...

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...