Perhaps the most significant paper I have yet to read on the subject of habitable zones has emerged from the University of Oxford, with collateral help from the Lamb and Flag on nearby St. Giles St. (a stout place), along with two scientists who claim no affiliation other than 'Earth.' The paper defines the Really Habitable Zone, that region around a star within which acceptable gins and tonic are likely to be found. "We suggest that planets in the Really Habitable Zone be early targets for the JWST, because by the time that thing finally launches we're all going to need a drink." Which is so patently true that I can only nod with approval. Adding that most habitable zone models now in play are defined by the need to justify the budget of the JWST to the US Congress, the authors proceed to note the difficulties in creating a habitable zone definition with which all astronomers can agree. What all astronomers can support, they argue, is a definition of what makes life worth living....

As we improve our instrumentation, the search for worlds where life can flourish will generate more and more Earth-sized targets for extended investigation. Here time plays an interesting role, for our own planet seen two billion years ago would present a different aspect than the Earth of today. Atmospheres evolve, a fact that Lisa Kaltenegger has studied in a series of papers in recent years, working with colleagues at Cornell's Carl Sagan Institute, where she is director. The result is a series of spectral templates applicable to Earth-like planets at various stages of evolution. We have only one known example of a living planet to work with, so Kaltenegger's atmospheric models are designed to match the Earth at different stages of development. The prebiotic Earth of 3.9 billion years ago is saturated with carbon dioxide, while what the paper refers to as Epoch 2, some 3.5 billion years ago, is a world without oxygen. Three more epochs can be defined covering the rise of...

Learning about the climate on exoplanets is not something that the designers of ESPRESSO had in mind. Installed at the European Southern Observatory's Very Large Telescope at Paranal (Chile), the Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations combines the light of the four VLT telescopes, making it a powerful instrument indeed. We have what is in effect a 16-meter telescope that really ramps up the capability of radial velocity methods. But climate? The case in point is WASP-76b, some 390 light years away in Pisces. So much of the excitement surrounding ESPRESSO has been its ability to drill down to detect small, rocky exoplanets, but this world is somewhere near Jupiter mass, considerably larger in radius, and hellishly close to its star, an F7-class object about 1.5 times as massive as the Sun. The planet orbits the star every 1.8 days at an orbital distance of 0.03 AU and appears to be tidally locked. The result: Temperatures in the area of...

M-class dwarfs within 100 light years are highly sought after objects these days, given that any transiting worlds around such stars will present unusually useful opportunities for atmospheric analysis. That's because these stars are small, allowing large transit depth -- in other words, a great deal of the star's light is blocked by the planet. Studying a star's light as it filters through a planetary atmosphere -- transmission spectroscopy -- can tell us much about the chemical constituents involved. We'll soon extend that with space-based direct imaging. While the discoveries we're making today are exciting in their own right, bear in mind that we're also building the catalog of objects that next generation ground telescopes (the extremely large, or ELT, instruments on the way) and their space-based cousins can examine in far greater depth. And it's also true that we are tuning up our methods for making sure that our planet candidates are real and not products of data...

330 light years from the Sun is the infant planet 2MASS 1155-7919 b, recently discovered in Gaia data by a team from the Rochester Institute of Technology. It’s a useful world to have in our catalog because we have no newborn massive planet closer to Earth than this one. Circling a star in the Epsilon Chamaeleontis Association, 2MASS 1155-7919 b is thought to be no more than 5 million years old, orbiting its host at roughly 600 times the Earth/Sun distance. A stellar association like Epsilon Chamaeleontis is a loose cluster, with stars that have a common origin but are no longer gravitationally bound as they move in rough proximity through space. RIT graduate student Annie Dickson-Vandervelde is lead author on the discovery paper: “The dim, cool object we found is very young and only 10 times the mass of Jupiter, which means we are likely looking at an infant planet, perhaps still in the midst of formation. Though lots of other planets have been discovered through the Kepler mission...

While we continue to labor over the question of planets around Alpha Centauri A and B, Proxima Centauri -- that tiny red dwarf with an unusually interesting planet in the habitable zone -- remains a robust source of new work. It’s surely going to be an early target for whatever interstellar probes we eventually send, and is the presumptive first destination of Breakthrough Starshot. Now we have news of a possible second planet here, though well outside the habitable zone. Nonetheless, Proxima Centauri c, if it is there, commands the attention. A new paper offers the results of continuing analysis of the radial velocity dataset that led to the discovery of Proxima b, work that reflects the labors of Mario Damasso and Fabio Del Sordo, who re-analyzed these data using an alternative treatment of stellar noise in 2017. Damasso and Del Sordo now present new evidence, working with, among others, Proxima Centauri b discoverer Guillem Anglada-Escudé, and incorporating astrometric data from...

We rightly celebrate exoplanet discoveries from dedicated space missions like TESS (Transiting Exoplanet Survey Satellite), watching the work go from initial concept to first light in space and early results. But let's not forget the growing usefulness of older data, tapped and analyzed in new ways to reveal hidden gems. Thus recent work out of the Carnegie Institution for Science, where Fabo Feng and Paul Butler have mined the archives of the Ultraviolet and Visual Echelle Spectrograph survey of 33 nearby red dwarf stars, a project operational from 2000 to 2007. The duo have uncovered five newly discovered exoplanets and eight more candidates, all found orbiting nearby red dwarf stars. Two of these are conceivably in the habitable zone, putting nearby stars GJ180 and GJ229A into position as potential targets for next-generation instruments. Both of these stars host super-Earths (7.5 and 7.9 times the mass of Earth), with orbital periods of 106 and 122 days respectively. Like the...

As if I don't have enough trouble figuring out acronyms, I now have to figure out how to pronounce acronyms. The issue comes up because a new NASA instrument now in use at Kitt Peak National Observatory is a spectrograph built at Penn State called NEID. Now NEID stands for NN-EXPLORE Exoplanet Investigations with Doppler spectroscopy. Here we have an acronym within an acronym, for NN-EXPLORE itself stands for the NASA-NSF Exoplanet Observational Research partnership that funds NEID. Here's the trick: The acronym NEID is not pronounced 'NEE-id' or 'NEED' but 'NOO-id.' The reason: Kit Peak is on land owned by the Tohono O'odham nation, and the latter pronunciation honors a verb that means something close to 'to see' in the Tohono O'odham language. As a person fascinated with linguistics, I'm delighted to see this nod to a language whose very survival is threatened by the small number of speakers (count me as one infinitely cheered by the resurrection of Cornish, for example). And as...

Among the discoveries announced at the recent meeting of the American Astronomical Society in Hawaii was TOI 700 d, a planet potentially in the habitable zone of its star. TOI stands for TESS Object of Interest, reminding us that this is the first Earth-size planet the Transiting Exoplanet Survey Satellite has uncovered in its data whose orbit would allow the presence of liquid water on the surface. The Spitzer instrument has confirmed the find, highlighting the fact that Spitzer itself, a doughty space observatory working at infrared wavelengths, is nearing the end of its operations. Thus Joseph Rodriguez (Center for Astrophysics | Harvard & Smithsonian): "Given the impact of this discovery - that it is TESS's first habitable-zone Earth-size planet - we really wanted our understanding of this system to be as concrete as possible. Spitzer saw TOI 700 d transit exactly when we expected it to. It's a great addition to the legacy of a mission that helped confirm two of the TRAPPIST-1...

TOI 1338b is a great catch, a circumbinary world that turned up in TESS data and was announced at the ongoing meeting of the American Astronomical Society in Hawai'i. Ravi Kopparapu (NASA GSFC) describes the discovery process in the essay below. The system lies 1,300 light years out in the constellation Pictor, with the planet transiting the larger star. Dr. Kopparapu's work on exoplanet habitability is well known to Centauri Dreams readers. See, for example, his How Common Are Potential Habitable Worlds in Our Galaxy?, which ran in 2014. He followed this up with a look at an unusual multi-planet system (Ravi Kopparapu: Looking at K2-72). Analyzing habitable zone possibilities around different kinds of stars, as well as modeling and characterizing exoplanet atmospheres, plays a major role in his research interests. Here Dr. Kopparapu tells us about the new world and the significant role of an intern in its discovery, reminding us that the opportunities for young scientists to make a...

The Egyptian monarch Khufu was the second pharaoh of the Fourth Dynasty, which dates him back to the earlier years of the Old Kingdom period around the 26th century BC. I mention this figure, about which all too little is known, because his name is a link between the great monuments of an early culture (Khufu seems to have commissioned the Great Pyramid of Giza) and present-day engineering. Imagine how wondrous the Great Pyramid would have been to the average passerby of the time, and then realize that Khufu's Hellenized name was Cheops, a monicker reflected in the acronym of our recently launched CHEOPS exoplanet observatory. I always enjoy untangling acronyms, some of which are more labored than others. Did you know, for example, that the name of the Japanese IKAROS solar sail is actually an acronym standing for Interplanetary Kite-craft Accelerated by Radiation Of the Sun? Then there's OSIRIS-REx (also satisfyingly Egyptian), which weighs in as Origins, Spectral Interpretation,...

An Australian amateur astronomer named Thiam-Guan Tan has made a name for himself in the realm of exoplanets. Tan participated in the discovery of an exoplanet that may orbit within its star's habitable zone. LHS 1140 b is a super-Earth some 41 light years from Earth that orbits a red dwarf star. Back in September of 2016, with a number of professional observatories looking at the host star, Tan provided key data to help verify the existence of LHS 1140b. "It was fortunate that I was able to catch a transit," said Tan, a retired engineer with a 12-inch telescope who has also discovered several supernovae. He is quoted in a newspaper called The West Australian as saying "That night, the Centre for Astrophysics had lined up five other telescopes across Australia and Hawaii to observe but they were all clouded out." Tan's work with exoplanet transits continues, an illustration of the role that talented amateurs with affordable equipment (Tan's telescope cost $15,000) can play. Image:...

Calling it a ‘chance discovery,’ the University of Warwick’s Boris Gänsicke recently presented the results of his team’s study of some 7,000 white dwarf stars, all of them cataloged by the Sloan Digital Sky Survey. One drew particular interest because chemical elements turned up in spectroscopic studies indicating something unusual. Says Gänsicke, “We knew that there had to be something exceptional going on in this system, and speculated that it may be related to some type of planetary remnant.” And that makes the star WDJ0914+1914 an example of what a stellar system that survived, at least partially, the red giant phase of its host star might look like as a planet orbits the Earth-sized white dwarf. This work, which draws on data from the European Southern Observatory’s X-shooter spectrograph at the Very Large Telescope in Chile, confirms hydrogen, oxygen and sulphur associated with the white dwarf, all found in a disk of gas around the star rather than being present in the white...

The interest in 'Oumuamua and comet 2I/Borisov makes it clear that interstellar neighbors wandering into our system generate loads of media coverage. And why not: Here is a way to study material from another stellar system while remaining within our own. 2I/Borisov, for example, reaches its closest approach to Earth in early December, closing to within roughly 300 million kilometers. Whatever pushed an object like this out of the parent system cannot be known, but we're likely dealing with gravitational disruption related to planets in the birth system. But more about that in a moment. For thanks to Yale University astronomers Pieter van Dokkum, Cheng-Han Hsieh, Shany Danieli, and Gregory Laughlin, we have a fine new image of 2I/Borisov. This was taken on November 24 using the W.M. Keck Observatory's Low-Resolution Imaging Spectrometer in Hawaii. The tail of the comet, according to van Dokkum, is about 160,000 kilometers long. Note the size comparison below to be reminded, as always,...

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...