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...

It would be useful to have a better handle on how and when water appeared on the early Earth. We know that comets and asteroids can bring water from beyond the ‘snowline,’ that zone demarcated by temperatures beyond which volatiles like water, ammonia or carbon dioxide are cold enough to condense into ice grains. For our Solar System, that distance in our era is 5 AU, roughly the orbital distance of Jupiter, although the snowline would have been somewhat closer to the Sun during the period of planet formation. So we have a mechanism to bring ices into the inner Solar System but don’t know just how large a role incoming ices played in Earth’s development. Knowing more about the emergence of volatiles on Earth would help us frame what we see in other stellar systems, as we evaluate whether or not a given planet may be habitable. Usefully, there are ways to study our planet’s formation that can drill down to its accretion from the materials in the original circumstellar disk. A new...

I’m collecting a number of documents on gravitational wave detection and unusual concepts regarding their use by advanced civilizations. It’s going to take a while for me to go through all these, but as I mentioned in the last post, I plan to zero in on the intriguing notion that civilizations with abilities far beyond our own might use gravitational waves rather than the electromagnetic spectrum to serve as the backbone of their communication system. It’s a science fictional concept for sure, though there may be ways it could be imagined for a sufficiently advanced culture. For today, though, let’s look at a new survey that targets highly unusual planets. Binaries Escorted by Orbiting Planets has an acronym I can get into: BEBOP. It awakens the Charlie Parker in me; I can almost smell the smoky air of a mid-20th century jazz club and hear the clinking of glasses above Parker’s stunning alto work. I was thinking about the great sax player because I had just watched, for about the...

Work on the Centauri Dreams internals continues, with the unwelcome result that the site has been popped offline twice because of a possible security problem. Needless to say, this has to be resolved before I can move forward on other aspects of the rebuild. While I deal with that issue, let me respond to a few backchannel questions about yesterday’s post on gas giants in red dwarf planetary systems. What I’m being asked about is my comment that gas giants like Jupiter, at similar distances and installation, around other classes of stars are common compared to what we see at red dwarfs. This has been a problematic issue, and the matter is a long way from achieving a consensus among researchers. A moment’s reflection yields the reason: Finding gas giants in outer system orbits around a star like the Sun is no easy matter. Radial velocity is most sensitive when dealing with large planets in tight orbits, which is why the first detections in main sequence stellar systems, beginning back...

Gas giant worlds like Jupiter may be uncommon around red dwarf stars, as a number of recent studies have found. It would be useful to tighten up the data, however, because many of the papers on this matter have used stellar samples at the high end of the mass range of M-dwarfs. At the Center for Astrophysics | Harvard & Smithsonian (CfA), Emily Pass and colleagues have gone to work on the question by looking at lower-mass M-dwarfs and working with a lot of them, some 200 in their sample, all within 15 parsecs. The question is not purely academic, for some scientists suggest that the presence of a Jupiter-class planet – not uncommon around G-class stars like the Sun – is a factor in the development of life. Migrating inward from a formation in the first few hundred million years of the Solar System’s existence, Jupiter would have stirred up plenty of icy cometary bodies through gravitational interactions. Impacts from this infall into the inner system likely delivered a great deal...

I might have mentioned the issues involving the James Webb Space Telescope’s MIRI instrument in my earlier post on in-flight maintenance and repair. MIRI is the Mid-Infrared Instrument that last summer had issues with friction in one of the wheels that selects between short, medium and longer wavelengths. Now there seems to be a problem, however slight, that affects the amount of light registered by MIRI’s sensors. The problems seem minor and are under investigation, which is a good thing because we need MIRI’s capabilities to study systems like GJ 486, where a transiting rocky exoplanet may or may not be showing traces of water in an atmosphere that may or may not be there. MIRI should help sort out the issue, which was raised through observations with another JWST instrument, the Near-Infrared Spectrograph (NIRSpec). The latter shows tantalizing evidence of water vapor, but the problem is untangling whether that signal is coming from the rocky planet or the star. This points to an...

It took a combination of astrometry and direct imaging to nail down exoplanet HIP 99770 b in Cygnus, and that’s a tale that transcends the addition of a new gas giant to our planetary catalogs. Astrometry measures the exact position and motion of stars on the sky, so that we are able to see the influence of an as yet unseen planet. In this work, astrometrical data from both the ESA Gaia mission and the earlier Hipparcos mission flag a world that is directly imaged by the Subaru Telescope extreme adaptive optics system, which enabled its near-infrared CHARIS spectrograph to see the target. Supporting work at the Keck Observatory using its Near-Infrared Camera and Keck II adaptive optics system allowed in combination with the CHARIS spectrum the discovery of the presence of water and carbon monoxide in the atmosphere, while the temperature was shown to be about ten times hotter than that of Jupiter. The joint measurements revealed a planet some 14-16 times the mass of Jupiter, in a...

Here’s a thought that puts a different spin on exoplanet studies. The speaker is Darryl Seligman (Cornell University): "The comets and asteroids in the solar system have arguably taught us more about planet formation than what we've learned from the actual planets in the solar system. I think that the interstellar comets could arguably tell us more about extrasolar planets than the extrasolar planets we are trying to get measurements of today." Seligman’s comment plays into the growing interest in interstellar objects that drift into our Solar System like 1/I ‘Oumuamua and 2/I Borisov. These may be the initial members of what is actually a large class of debris from other stars that we are only now learning how to detect. Among the many things we have yet to refine in our understanding of ‘Oumuamua is its actual size. Projections of 115 by 111 by 19 meters are deduced from its brightness and the changes produced by its apparently tumbling motion. The interstellar interloper is too...

The problem with Alpha Centauri is that the system is too close. I don’t refer to its 4.3 light year distance from Sol, which makes these stars targets for future interstellar probes, but rather the distance of the two primary stars, Centauri A and B, from each other. The G-class Centauri A and K-class Centauri B orbit a common barycenter that takes them from a maximum of 35.6 AU to 11.2 AU during the roughly 80 year orbital period. That puts their average distance from each other at 23 AU. So the average orbital distance here is a bit further than Uranus’ orbit of the Sun, while the closest approach takes the two stars almost as close as the Sun and Saturn. Habitable zone orbits are possible around both stars, making for interesting scenarios indeed, but finding out just how the system is populated with planets is not easy. We’ve learned a great deal about Proxima Centauri’s planets, but teasing out a planetary signature from our data on Centauri A and B has been frustrating despite...

The presence of water in the circumstellar disk of V883 Orionis, a protostar in Orion some 1300 light years out, is not in itself surprising. Water in interstellar space is known to form as ice on dust grains in molecular clouds, and clouds of this nature collapse to form young stars. We would expect that water would be found in the emerging circumstellar disk. What new work with data from the Atacama Large Millimeter/submillimeter Array (ALMA) shows is that such water remains unchanged as young star systems evolve, a chain of growth from protostar to protoplanetary disk and eventually planets and water-carrying comets. John Tobin, an astronomer at the National Science Foundation’s National Radio Astronomy Observatory (NRAO), is lead author on the paper on this work: “We can think of the path of water through the Universe as a trail. We know what the endpoints look like, which are water on planets and in comets, but we wanted to trace that trail back to the origins of water. Before...

If there is a Planet Nine out there, I assume we’ll find it soon. That would be a welcome development, in that it would imply the Solar System isn’t quite as odd as it sometimes seems to be. We see super-Earths – and current thinking seems to be that this is what Planet Nine must be – in other stellar systems, in great numbers in fact. So it would stand to reason that early in its evolution our system produced a super-Earth, one that was presumably nudged into a distant, eccentric orbit by gravitational interactions. The gap in size between Earth and the next planet up in scale is wide. Neptune is 17 times more massive than our planet, and four times its radius. Gas giant migration surely played a role in the outcome, and when considering stellar system architectures, it’s noteworthy as well that all that real estate between Mars and Jupiter seems to demand something more than asteroidal debris. To make sense of such issues, Stephen Kane (University of California, Riverside) has run...

We’re beginning to learn how common planets are around stars of various types, but M-dwarfs get special attention given their role in future astrobiological studies. As I’ve just been talking about CARMENES, the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Échelle Spectrographs program, I’ll fold in today’s news about their release of 20,000 observations covering more than 300 stars, for we can mine some data here about planet occurrence rates. 59 new planets turn up in the spectroscopic data gathered at the Calar Alto Observatory in Span, with about 12 thought to be in the habitable zone of their star. I’ll await with interest our friend Andrew LePage’s assessment. His habitable zone examinations serve as a highly useful reality check. I mentioned spectrographic data above. The CARMENES instruments are built for optical as well as near-infrared studies, and have been used to explore nearby red dwarfs and their possible planets since...

Let’s look at a second red dwarf planet in this small series on such, this one being Wolf 1069b. I want to mention it partly because of the prior post on K2-415b, where we had the good fortune to be dealing with a transiting world around an M-dwarf that should be useful in future atmospheric characterization efforts. Wolf 1069b, by contrast, was found by radial velocity methods, and I’m less interested in whether or not it’s in a ‘habitable’ orbit than in the system architecture here, which raises questions. This work, recounted in a recent paper in Astronomy & Astrophysics, describes a planet that is not just Earth-sized, as is K2-415b, but roughly equivalent to Earth in mass, making a future search for biosignatures interesting once we have the capability of collecting photons directly from the planet. If the planet has an atmosphere, argue the authors of the paper, its surface temperature could reach 13 degrees Celsius, certainly a comfortable temperature for liquid water. A...