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...

I want to mention the recent confirmation of K2-415b because this world falls into an interesting category: Planets with major implications for studying their atmospheres. Orbiting an M5V M-dwarf every 4.018 days at a distance of 0.027 AU, this is not a planet with any likelihood for life. Far from it, given an equilibrium temperature expected to be in the range of 400 K (the equivalent figure for Earth is 255 K). And although it’s roughly Earth-sized, K2-415b turns out to be at least three times more massive. What this planet has going for it, though, is that it transits a low mass star, and at 70 light years, it’s close. Consider: If we want to take advantage of transmission spectroscopy to study light being filtered through the planetary atmosphere during ingress and egress from the transit, nearby M-dwarf systems make ideal targets. Their habitable zones are close in, so we get frequent transits around small stars. But the number of Earth-sized transiting worlds around nearby...

LHS 475b, a planet whose diameter is all but identical to Earth's, makes news not so much because of what it is but because of what it tells us about studying the atmospheres of small rocky worlds. Credit for the confirmation of this planet goes to the NIRSpec (Near-Infrared Spectrograph) instrument aboard the James Webb Space Telescope, and LHS 475b marks the telescope’s first exoplanet catch. Data from the Transiting Exoplanet Survey Satellite (TESS) were sufficient to point scientists toward this system for a closer look. JWST confirmed the planet after only two transits. Based on this detection, the Webb telescope is going to live up to expectations about its capabilities in exoplanet work. NIRSpec is a European Space Agency contribution to the JWST mission, and a major one, as the instrument’s multi-object spectroscopy mode is able to obtain spectra of up to 100 objects simultaneously, a capability that maximizes JWST observing time. No other spectrograph in space can do this,...