Given our intense scrutiny of planets around other stars, I find it interesting how little we know even now about the history of our own Sun, and its varying effects on habitability. A chapter in an upcoming (wildly overpriced) Elsevier title called The Archean Earth is informative on the matter, especially insofar as it illuminates which issues most affect habitability and how the values for these vary over time. It’s also a fascinating look at changing conditions on Venus, Earth and Mars. We know a great deal about the three worlds from our local and planetary explorations, but all too little when it comes to explaining the evolution of their atmospheres and interior structures. But it’s important to dig into all this because as Stephen Kane, director of The Planetary Research Laboratory at UC-Riverside and colleagues point out, we seem to be looking at the end state of habitability on both Mars and Venus, meaning that our explorations of these worlds should yield insights into...

Over the weekend I learned about Joseph Haydn’s Symphony No. 47, unusual in that it offers up some of its treasures in perfect symmetry. Dubbed ‘The Palindrome,’ the symphony’s third movement, Minuetto e Trio, is crafted to play identically whether attacked normally – moving forward through the score – or backwards. You can check this out for yourself in this YouTube video, or on this non-auditory reference. The pleasure of unexpected symmetry is profound, and when seen through the eyes of our spacecraft, can be startling. Consider the storied star Vega. We see this system from our perspective at a very low inclination angle relative to its rotational axis, as if we were looking down from above the star’s pole. This face-on perspective is profoundly interesting when examined through our space-borne astronomical assets. In the image below, we get two views of Vega’s disk, from Hubble and then JWST. Image: The disk around Vega as seen by Hubble (left) and Webb (right). Hubble detects...

If you follow the fortunes of the stars closest to us, you know that Barnard’s Star has always excited interest, both because of its proximity to our system (about six light years) but also because of the early work on the star performed by Peter Van de Kamp at Sproul Observatory (Swarthmore College). That work, which ran until the early 1970s, initially appeared to show a Jupiter-class planet at the star but the results were later explained as instrumentation errors in Van de Kamp’s equipment. It was a cautionary tale, but credit the astronomer for working tirelessly using astrometry to attempt to validate a conclusion we now take for granted: There are planets around other stars. In 2018 we seemed to have a solid detection of a much different planet candidate via Guillem Anglada-Escudé (Queen Mary University, London) and Ignasi Ribas (Institute of Space Studies of Catalonia and the Institute of Space Sciences, CSIC in Spain), indicating a super-Earth of 3.3 Earth masses in an orbit...

Some years back I read a science fiction story in which the planet where the action took place orbited an F-class star. That was sufficiently odd to get my attention, and I began to pay attention to these stars, which represent on the order of 3 percent of all stars in the galaxy. Stars like our G-class Sun weigh in at about 7 percent, while the vast majority of stars are M-dwarfs, still our best chances for life detection because of the advantages they offer to our observing technologies, including deep transits and lower stellar brightness for direct imaging purposes. F-stars are intriguing despite the fact that they tend to be somewhat larger than the Sun (up to 1.4 times its mass) and also hotter (temperatures in the range of 6200-7200 K). Back in 2014, I looked at the work of Manfred Cuntz (University of Texas at Arlington), who had performed a study examining radiation levels in these stars and the damage that DNA would experience with an F-star in the sky at various stages of...

“What is this fascination of yours with small red stars?” a friend asked in a recent lunch encounter, having seen something I wrote a few years back about TRAPPIST-1 in one of his annual delvings into the site. “They’re nothing like the Sun, to quote Shakespeare, and anyway, even if they have planets, they can’t support life. Right?” Hmmm. The last question is about as open as a question can get. But my friend is on to something, at least in terms of the way most people think about exoplanets. My fascination with small red stars is precisely their difference from our familiar G-class star. An M-dwarf planet bearing life would be truly exotic, in an orbit lasting mere days rather than months (depending on the class of M-dwarf), and perhaps tidally locked, so inhabitants would see their star fixed in the sky. How science fictional can you get? And we certainly don’t have enough data to make the call on life around any of them. Let’s talk a minute about how we classify small red stars,...

Great observatories work together to stretch the boundaries of what is possible for each. Data from the Chandra X-ray Observatory were used in tandem with the James Webb Space Telescope, for example, to observe the death of a star as it was consumed by a black hole. JWST’s infrared look at this Tidal Disruption Event (TDE) helped show the structure of stellar debris in the accretion disk of the black hole, while Chandra charted the high-energy processes at play in the cataclysmic event. Or have a look at the image below, combining X-ray and infrared data from these two instruments along with the European Space Agency’s XMM-Newton, the Spitzer Space Telescope and optical data from Hubble and the European Southern Observatory's New Technology Telescope to study a range of targets. Image: Four composite images deliver dazzling views from NASA’s Chandra X-ray Observatory and James Webb Space Telescope of two galaxies, a nebula, and a star cluster. Each image combines Chandra’s X-rays — a...

Europa Clipper is scheduled to launch on October 10, with arrival at Jupiter in 2030. That will keep subsurface oceans on our minds as we tangle with the problems of analyzing water locked under kilometers of ice. Some moons, of course, help us out. Enceladus spews watery materials into space through cracks in its crust, making flybys through its geysers a possibility for snagging samples. Europa Clipper may find further evidence of the much less dramatic plume activity that has been spotted on Europa. Clipper’s SUrface Dust Analyzer (SUDA) would prove vital in such analysis. If cellular material is found in an ice grain snared from an orbital pass, would we be able to detect it? The answer may be found in laboratory work with a common bacteria that thrives in the waters off Alaska. As explained in new work out of the University of Washington and the Freie Universität Berlin, the bacterium Sphingopyxis alaskensis is made to order for such studies. It is smaller than Escherichia coli...

Just a few weeks ago I wrote about stellar interactions, taking note of a concept advanced by scientists including Ben Zuckerman and Greg Matloff that such stars would make for easier interstellar travel. After all, if a star in its rotation around the Milky Way closes to within half a light year of the Sun, it’s a more feasible destination than Alpha Centauri. Of course, you have to wait for the star to come around, and that takes time. Zuckerman (UCLA), working with Bradley Hansen, has written about the possibility that close encounters are when a civilization will attempt such voyages. I have a further idea along the lines of motion through the galaxy and its advantages to explorers, and it’s one that may not require tens of thousands of years of waiting. We’d like to get to another star system because we’re interested in the planets there, so what if an interstellar planet nudges into nearby space? I’ll ignore Oort Cloud perturbations and the rest to focus on a ‘rogue’ or...

Planet formation is a fascinating subtopic of the exoplanet hunt, and it may just have produced the first exoplanet detection in data that go back as far back as 1981, though the event in question has never been confirmed as being caused by a planet. I learned this through a paper sent me recently by Jean Schneider (Observatoire de Paris), who along with colleague Danielle Briot wrote about the early days of transit searches in a chapter for the Handbook of Exoplanets (Springer, 2018). I want to dig deeper into that chapter in a later post, but for now, I note that the planet Beta Pictoris b, discovered in 2008 and orbiting an infant star 63 light years from Earth, may have transited in 1981, according to subsequent papers on the matter. The debris disk around the primary has long fascinated astronomers and it has been investigated for the possible presence of comet-like bodies and subjected to direct imaging searches, which revealed Beta Pictoris b and confirmed it in 2009. But the...

I'm going to start in the Kuiper Belt this morning before going further out, because the news that the Belt may extend much further than expected reminds us of the nature of exploration. The New Horizons spacecraft, well beyond Pluto’s orbit and approaching 60 AU from the Sun, is finding more dust than expected. Our theoretical models didn’t see that coming. In fact, the dust produced by collisions between Kuiper belt objects was thought to decline as we approached the Belt’s outer edge. So just where is that outer edge? It had been pegged around 50 AU but now looks more like 80 AU, if not further out, a finding corroborated by the fact that New Horizons scientists have used Earth-based resources like the Subaru Telescope in Hawaii to find numerous KBOs beyond the assumed boundary. Is this a new population of Solar System objects, or are we actually seeing something more mundane, such as radiation pressure pushing inner belt dust further out than would be expected? It takes patient...

Some things just run in families. If you look into the life of Otto Struve, you’ll find that the Russian-born astronomer was the great grandson of Friedrich Georg Wilhelm von Struve, who was himself an astronomer known for his work on binary stars in the 19th Century. Otto’s father was an astronomer as well, as was his grandfather. That’s a lot of familial energy packed into the study of the stars, and the Struve of most recent fame (Otto died in 1963) drew on that energy to produce hundreds of scientific papers. Interestingly, the man who was director at Yerkes and the NRAO observatories was also an early SETI advocate who thought intelligence was rife in the Milky Way. Of Baltic-German descent, Otto Struve might well have become the first person to discover an exoplanet, and therein hangs a tale. Poking around in the history of these matters, I ran into a paper that ran in 1952 in a publication called The Observatory titled “Proposal for a Project of High-Resolution Stellar Radial...

Our recent conversations about the likelihood of life elsewhere in the universe emphasize how early in the search we are. Consider recent work on TRAPPIST-1, which draws on JWST data to tell us more about the nature of the seven planets there. On the surface, this seven-planet system around a nearby M-dwarf all but shouts for attention, given that we have three planets in the habitable zone, all of them of terrestrial size, as indeed are all the planets in the system. Moreover, as an ultracool dwarf star, the primary is both tiny and bright in the infrared, just the thing for an instrument like the James Webb Space Telescope to harvest solid data on planetary atmospheres. This is a system, in other words, ripe for atmospheric and perhaps astrobiological investigation, and Michaël Gillon (University of Liége), the key player in discovering its complexities, points in a new paper to how much we’ve already learned. If its star is ultracool, the planetary system at TRAPPIST-1 can also be...

Back before we knew for sure there were planets around other stars, the universe seemed likely to be ordered. If planet formation was common, then we'd see systems more or less like our own, with rocky inner worlds and gas giants in outer orbits. And if planet formation was a fluke, we'd find few planets to study. All that has, of course, been turned on its head by the abundant discoveries of exoplanets galore. And our Solar System turns out to be anything but a model for the rest of the galaxy. In today's essay, Don Wilkins looks at several recent discoveries that challenge planet formation theory. We can bet that the more we probe the Milky Way, the more we'll find anomalies that challenge our preconceptions. by Don Wilkins The past few decades have not been easy on planet formation theories. Concepts formed on the antiquated Copernican speculation, the commonality of star systems identical to the Solar System, have given way to the strangeness and variety uncovered by Kepler,...

The ancient notion of the ‘music of the spheres’ sounds primitive until you learn something about planetary dynamics. Gravity is wondrous and can nudge planets in a given system into orbits that show an obvious mathematical ratio. Two planets in resonance can emerge, for instance, in a 2:1 ratio, where one goes around its star twice in the time it takes the second to orbit it once. Such linkages might seem almost coincidental to the casual observer until the coincidences begin to pile up. In the exoplanet system at HD 110067, for example, resonance flourishes, so much so that we have six planets moving in a ‘resonance chain.’ No coincidence here, just gravity at work, although an actual coincidence is that just when I finished a post highlighting system dynamics in closely packed environments like TRAPPIST-1 as a ‘brake’ on inbound comets, an international team should reveal HD 110067’s resonance chain. It’s a beauty, for all six planets not only move in harmonic rhythm but also turn...

Although I think most astronomers have assumed Proxima Centauri was bound to the central binary at Alpha Centauri, the case wasn’t definitively made until fairly recently. Here we turn to Pierre Kervella (Observatoire de Paris), Frédéric Thévenin (Côte d’Azur Observatory) and Christophe Lovis (Observatoire Astronomique de l'Université de Genève). We last saw Dr. Kervella with reference to a paper on aerographite as a sail material, but his work has appeared frequently in these pages, analyzing mission trajectories and studying the Alpha Centauri system. Here he and his colleagues use HARPS spectrographic data to demonstrate that we have at Centauri a single gravitationally bound triple system. This is important stuff; let me quote the paper on this work to explain why (italics mine): Although statistical considerations are usually invoked to justify that Proxima is probably in a bound state, solid proof from dynamical arguments using astrometric and radial velocity (RV) measurements...

How extraordinary that the nearest star to Earth is actually a triple system, the tight central binary visually merged as one bright object, the third star lost in the background field but still a relatively close 13000 or so AU from the others. Humans couldn’t have a better inducement to achieve interstellar flight on the grounds of these stars alone. We get three stellar types: The G-class Centauri A, the K-class Centauri B, both of which are capable of hosting planets, perhaps habitable, of their own. And then we have Proxima Centauri, opening up M-class red dwarf stars to close investigation, and we already know of a planet in the habitable zone there, adding to the zest of the venture. If extraterrestrial beings in a system like this would have even more inducement to travel, with another star’s planets perhaps as close to them as our own system’s worlds are to us, we humans are also spurred to undertake a journey, because 4.2 light years is a mere stone’s throw in the overall...

We’re building some remarkably large telescopes these days. Witness the Giant Magellan Telescope now under construction in Chile’s Atacama desert. It’s to be 200 times more powerful than any research telescope currently in use, with 368 square meters of light collection area. It incorporates seven enormous 8.5 meter mirrors. That makes exoplanet work from the Earth’s surface a viable proposition, but look at the size of the light bucket we need to make it work. Three mirrors like that shown below are now in place, and the University of Arizona’s Mirror Lab is building number 6 now. Image: University of Arizona Richard F. Caris Mirror Lab staff members Damon Jackson (left) and Conrad Vogel (right) in the foreground looking up at the back of primary mirror segment five, April 2019. Credit: Damien Jemison; Giant Magellan Telescope - GMTO Corporation. CC BY-NC-ND 4.0. Imaging an exoplanet from the Earth’s surface is complicated by the Rayleigh Limit, which governs the resolution of our...

Centauri Dreams regular Dave Moore just passed along a paper of considerable interest for those of us intrigued by planetary systems around red dwarf stars. The nearest known exoplanet of roughly Earth’s mass is Proxima Centauri b, adding emphasis to the question of whether planets in an M-dwarf’s habitable zone can indeed support life. From the standpoint of system dynamics, that often comes down to asking whether such a planet is not so close to its star that it will become tidally locked, and whether habitable climates could persist in those conditions. The topic remains controversial. But there are wide variations between M-dwarf scenarios. We might compare what happens at TRAPPIST-1 to the situation around Proxima Centauri. We have an incomplete view of the Proxima system, there being no transits known, and while we have radial velocity evidence of a second and perhaps a third planet there, the situation is far from fully characterized. But TRAPPIST-1’s superb transit...

A search for liquid water on a planetary surface may be too confining when it comes to the wide range of possibilities for supporting life. We see that in our own Solar System. Consider the growing interest in icy moons like Europa and Enceladus, where there is no possibility of surface water but a potentially rich environment under a thick layer of ice. Extending these thoughts into the realm of exoplanets reminds us that our calculations about how many life-bearing worlds are out there may be in need of revision. This is the thrust of work by Lujendra Ojha (Rutgers University) and colleagues, as developed in a paper in Nature Communications and presented at the recent Goldschmidt geochemistry conference in Lyon. What Ojha and team point out is that radiogenic heating can maintain liquid water below the surface of planets in M-dwarf systems, and that added into our astrobiological catalog, such worlds, orbiting a population of stars that takes in 75 percent or more of all stars in...