I’ve always liked the image of Proxima Centauri b that the ESO’s Martin Kornmesser has conjured directly below, and have used it in a couple of previous articles about the planet. Indeed, you’ll see it propagated widely when the topic comes up. But like all of these exoplanet artist impressions, it’s made up of educated guesses, as it has to be. We don’t even know, for example, whether the world we see here even has an atmosphere, as depicted. Whether or not it does is important because it affects the possibilities for life around the star nearest to our own. Twenty times closer to its star than the Earth is to the Sun, Proxima b nonetheless receives roughly the same energy, meaning we could have surface temperatures there that would support liquid water on the surface. But the planet also receives 400 times more X-rays than the Earth, which leads the University of Geneva’s Christophe Lovis to ask: “Is there an atmosphere that protects the planet from these deadly rays? And if this...

Studying the atmospheres of exoplanets is a process that is fairly well along, especially when it comes to hot Jupiters. Here we have a massive target so close to its star that, when a transit occurs, we can look at the star's light filtering through the atmosphere of the planet. Even so, clouds are a problem because they prevent accurate readings of atmospheric composition below the upper cloud layers. Aerosols -- suspended solid particles or droplets in a gas -- are common, range widely in composition, and make studying a planet's atmosphere harder. We'd like to learn more about which aerosols are where and in what kind of conditions, for we have a useful database of planets to work with. Over 70 exoplanets currently have transmission spectra available. A wide range of cloud types, many of them exotic indeed, have been proposed by astronomers to explain what they are seeing. Imagine clouds of sapphire, or rubies, which is essentially what we get with aerosols of aluminum oxides...

You would think that the orbits of planets would align closely with the spin of their star, since they emerged from the same primordial disk. Many planets do just that, and in our own system, the orbits of the planets are aligned within 6 degrees of the Sun's rotation. But the numerous cases of star-planet orbital misalignment around other stars cause us to question whether these systems formed out of alignment or were influenced by later perturbations. A massive companion in a wide orbit could do the trick, and other mechanisms to tilt the orbital or spin axes are discussed in the literature. To examine the question, the Rossiter-McLaughlin effect comes into play. Discovered by studying binary stars, the effect is named after the two University of Michigan graduate students who figured it out back in the 1920s. They realized that as a star rotates, part of it seems to be coming toward the observer, creating a blueshift, while the other side seems to be moving away, producing a...

It will surprise few Centauri Dreams readers that at least some brown dwarfs have bands of clouds, just as we see similar bands on our Solar System's largest planet. In fact, three brown dwarfs have recently shown signs of cloud banding, and today's subject, Luhman 16, has previously been analyzed in terms of large cloud patches. I think new work based on data from the European Southern Observatory's Very Large Telescope (VLT) in Chile may be less significant for what it says about brown dwarfs than what it says about how we study them. Image: Illustration comparing the masses of planets, brown dwarfs, and stars. Credit: NASA/JPL-Caltech/R. Hurt (IPAC). For the work in question, reported in a paper from Maxwell Millar-Blanchaer (Caltech) and colleagues, is the first time polarimetry has been put to work to infer bands in brown dwarf clouds. Polarization tells us the direction that a light wave oscillates. Millar-Blanchaer likens polarimetric instruments to polarized sunglasses --...

Transit timing variations are useful to astronomers trying to learn what forces are acting upon a known exoplanet. They could eventually help us ferret out the existence of a sufficiently large moon, for example, though we have yet to confirm one. But they also show us how much impact other planets in the same system can have upon the planet being observed. All this is why the Kepler-88 system has been high on the list of interesting targets for astronomers. Before the recent discovery of a new gas giant, we knew about Kepler-88 b and c, one of them (the outer world Kepler-88 c) about 20 times more massive than Kepler-88 b, a planet less massive than Neptune. The story here was the mean motion resonance, in which planet c, a Jupiter-mass world, orbits the star in 22 days while Kepler-88 b orbits in 11: Two orbits of b in the time it takes c to make a single orbit. Planet b is the only transiting planet in this system; Kepler-88 c was confirmed by radial velocity methods. The mass...

We may be measuring planetary temperatures with less than optimum tools. Calling it a "new phenomenon," Cornell University's Nikole Lewis described the background of a just published paper looking into hot Jupiter temperatures. Lewis had been increasingly puzzled by earlier work on the matter, which produced temperatures colder than scientists expected. The deputy director of the Carl Sagan Institute, Lewis joined colleagues Ryan MacDonald and Jayesh Goyal in looking for the reason, reporting their results in Astrophysical Journal Letters. What emerged was the need to fine-tune our analysis of exoplanet atmospheres, as delivered by the technique called transmission spectroscopy, in which the light of a parent star is filtered through a planetary atmosphere during a transit. Have a look, for example, at an illustration of the hot-Jupiter WASP-43b as it transits its star. Scientists have been able to construct temperature maps for the planet as well as probing its atmosphere to...

Objects of interstellar origin in our own Solar System continue to draw attention. Comets from other stars like 2I/Borisov give us the chance to delve into the composition of different stellar systems, while the odd ‘Oumuamua still puzzles astronomers. Comet? Asteroid? Now we have a paper from Fathi Namouni (Observatoire de la Côte d'Azur, France) and Maria Helena Morais (Universidade Estadual Paulista, Brazil) targeting what the duo believe to be a population of asteroids captured from other stars in the distant past. Published in Monthly Notices of the Royal Astronomical Society, the paper relies on a high-resolution statistical search for stable orbits, ‘unwinding’ these orbits back in time to explain the location of certain Centaurs, asteroids moving perpendicular to the orbital plane of the planets and other asteroids. Centaurs, most of which do not occupy such extreme positions, are a population of asteroids moving between the outer planets in what have until now been...

I'm keeping an eye on the recent attention being paid to Proxima Centauri c, the putative planet whose image may have been spotted by careful analysis of data from the SPHERE (Spectro-Polarimetric High-Contrast Exoplanet Research) imager mounted on the European Southern Observatory's Very Large Telescope. A detection by direct imaging of a planet found first by radial velocity methods would be a unique event, and the fact that this might be a planet in the nearest star system to our own makes the story even more interesting. I hasten to add that this is not Proxima b, the intriguing planet in the star's habitable zone, but the much larger candidate world, likely a mini-Neptune, that has been identified but not yet confirmed. Proxima Centauri c could use a follow-up to establish its identity, and this direct imaging work would fit the bill if it holds up. But for now, the planet is still a candidate rather than a known world. From the paper: While we are not able to provide a firm...

What an exceptional system the one around HD 158259 is! Here we have six planets, uncovered with the SOPHIE spectrograph at the Haute-Provence Observatory in the south of France, with the innermost world also confirmed through space-based TESS observations. Multiple things jump out about this system. For one thing, all six planets are close to, but not quite in, a 3:2 resonance. That 'close to' tells the tale, for researchers believe there are clues to the formation history of the system within their observations of this resonance. Image: In the planetary system HD 158259, all pairs of subsequent planets are close to the 3:2 resonance : the inner one completes about three orbits as the outer completes two. Credit & Copyright: UNIGE/NASA. The primary, HD 158259, is itself interesting, in that it's a G-class star about 88 light years out, an object just a little more massive than our Sun. But tucked well within the distance of Mercury from the Sun we find all six of the thus far...

We're learning interesting things about 2I/Borisov, the first interstellar comet discovered entering our Solar System ('Oumuamua may have been a comet as well, but the lack of an active gas and dust coma makes it hard to say for sure). Moving at 33 kilometers per second, 2I/Borisov is on a trajectory clearly indicating an interstellar origin. Now two different studies have shown that in terms of composition, the visiting object is unlike most of the comets found in our own system. Both the Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA) have found levels of carbon monoxide (CO) higher than expected, a concentration greater than any comet yet detected within 2 AU of the Sun (about 300 million kilometers). The ALMA team finds the CO concentration to be somewhere between 9 and 26 times higher than inner system comets, while Hubble sees levels at least 50 percent more abundant than the average of comets in the inner system. Dennis Bodewits (Auburn...

What intrigues me about Kepler-1649c, a newly discovered planet thrust suddenly into the news, isn't the fact that it's potentially in its star's habitable zone, nor that it is close to being Earth-sized (1.06 times Earth's radius). Instead, I'm interested in the way it was found. For this is a world turned up in exhaustive analysis of data from the original Kepler mission. Bear in mind that data from the original Kepler field ceased being gathered a full seven years ago. I share Jeff Coughlin's enthusiasm on the matter. Coughlin is an astronomer affiliated with the SETI Institute who is a co-author on the new paper, which appears in Astrophysical Journal Letters. One of the goals of the mission that began as Kepler and continued (on different star fields) as K2 was to find the fraction of stars in the galaxy that have planets in the habitable zone, using transit methods for initial detection and radial velocity follow-up on Earth. Of the new find, made with an international team of...

The interstellar object we call 'Oumuamua was bound to be fascinating no matter what it actually was. You discover the first incoming object from interstellar space only once. But this one had its own share of peculiarities. Here was what was assumed to be a comet, but one that showed no outgassing as it reached perihelion and in fact seemed to be unusually dry. Here was an object of an apparently elongated shape, an aspect ratio with which we had nothing to compare in our own system. A tiny but detectable acceleration on the way out of the system seemed to indicate later outgassing, but how was that consistent with earlier data? I think Harvard's Avi Loeb was exactly right to point out that among the possible explanations of new objects, we can't disregard the possibility of a technology from another civilization. That 'Oumuamua was a natural object is an obvious default position, but we are at a stage in our understanding of the cosmos when we realize that the conditions for life...

The brown dwarf 2MASS J10475385+2124234 is about the size of Jupiter, but maybe 40 times more massive. 33.2 light years from Earth, this object is in that category between planet and star, not massive enough to launch the same kind of nuclear reactions that power the Sun, but considerably more massive than any planet. Combining two tools -- the Very Large Array (VLA) and NASA's Spitzer Space Telescope -- scientists have now measured the wind speed here. Katelyn Allers (Bucknell University), who led the research team, realized that the combination of radio observations (VLA) and infrared (Spitzer) would make this kind of measurement possible, and expressed surprise that no one else had thought to do it before. After all, we already knew that the rotation period of Jupiter found through radio measurements differs from the period found at visible and infrared wavelengths. That disparity is key to the new measurement. For the difference is the result of two separate phenomena. Radio...

We looked recently at Voyager 2's flyby of Uranus, via a new paper that examined the craft's magnetometer data to draw out information about the planet's magnetic environment. Science fiction author Stanley Weinbaum, author of the highly influential "A Martian Odyssey" in 1935, christened Uranus 'The Planet of Doubt' in a short story of the same name. Weinbaum couldn't have known about the world's magnetic field axis, which we've learned is tilted 60 degrees away from its spin axis. The latter itself is 98 degrees off its orbital plane. Doubtful planet indeed. Here we have a world that is spinning on its side, one that demands answers as to how it got that way. A giant impact at some point in its history is a natural assumption, but how do we explain the fact that the Uranian moons as well as the planet's ring system all show the same 98 degree orbital tilt as their parent? Back in 2011, a team led by Alessandro Morbidelli (Observatoire de la Cote d'Azur) ran a variety of simulations...

The Kepler mission gave us, along with plenty of exoplanetary scenarios, a statistical look at a particular patch of sky, one containing parts of Lyra, Cygnus and Draco. Some of the stars within that field were close (Gliese 1245 is just 15 light years out), but the intention was never to home in on nearby systems. Most of the Kepler stars ranged from 600 to 3,000 light years away. Instead, Kepler would produce an overview of planets around different stellar types, including some in the habitable zone of their stars. As with all such observations, we're limited by the methods chosen, which in Kepler's case involved transits of the host star. TESS, the Transiting Exoplanet Survey Satellite, likewise uses the transit method, though with particular reference to broad sky coverage and close, bright stars. We can deploy the widely anticipated James Webb Space Telescope, to be launched next year, to follow up interesting finds, but let's also consider how useful the Wide Field Infrared...

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...