Proxima Centauri b, that highly interesting world around the nearest star, is about 0.05 AU out from its primary. The figure leaps out to anyone new to red dwarf stars, because it's so very close to the star itself, well within the orbit of Mercury in our own system. But these are small, dim stars compared to our Sun, and hugging the star is essential to remain in the habitable zone. That also makes for very short years -- Proxima b completes an orbit every 11.2 days. Guillem Anglada-Escudé and colleagues reminded us in the discovery paper that among the many things we have to ask about this planet is whether or not it has a strong magnetic field. Because Proxima Centauri is known for flare activity, not to mention 400 times the X-ray flux the Earth receives. A magnetic field could help the planet hang on to its atmosphere, but just how strong would it need to be? Like any M-dwarf planet, then, Proxima b seems vulnerable. This thinking has ramifications much closer to home. We...

TRAPPIST continues to be my favorite astrophysical acronym. Standing for Transiting Planets and Planetesimals Small Telescope, the acronym flags a robotic instrument at the La Silla Observatory in Chile that is operated by the the Institut d'Astrophysique et Géophysique (University of Liège, Belgium) in cooperation with the Geneva Observatory. The name is a nod to the branch of the Cistercian order of monks called Trappists, whose beer is world-renowned and closely associated with Belgium itself (although also brewed in the Netherlands and a few other countries). A jolly telescope indeed. You'll recall TRAPPIST-1 as the far more approachable term for the red dwarf star 2MASS J23062928-0502285, a bit over 39 light years away in the direction of the constellation Aquarius. A 2016 paper in Nature announced three rocky planets orbiting the star, one of which could conceivably be in its habitable zone, where liquid water can exist on the surface. Now we have a helpful follow-up...

Alpha Centauri A and B, the two primary stars of the Alpha Centauri threesome, orbit a common center of gravity, with an average separation of 23.7 AU. But bear in mind that this average covers wider ground. The separation can close to about 11 AU or widen to as far as 36 AU. I bring these distances up because it's an open question whether there are planets around either of these stars. The possibility exists that we might find planets around both, and of course we already know of that interesting planet circling nearby Proxima Centauri. Do we have examples of close binaries in which we find a planet around each star? Until late August, the closest known binary system with planets orbiting both individual stars showed a separation of 1000 AU. But now we have the twin stars HD 133131A and HD 133131B. Around the former we have two planets, one whose minimum mass is about 1.5 times Jupiter's mass, the other with a minimum of about half Jupiter's mass. The second star hosts a planet of...

Meeting people I've written about is always a pleasure at gatherings of the interstellar-minded, and I was delighted to run into Victoria Meadows (University of Washington) in the lobby of our hotel on the final day of the Breakthrough Starshot meetings. Rory Barnes is a colleague of Meadows at UW and recently described the research underway at the Virtual Planetary Laboratory there, at which Meadows is the director. Barnes' essay Opportunities and Obstacles for Life on Proxima b appeared as a guest post on the Pale Red Dot site. I wished I had time to discuss Proxima with Meadows, but our meeting was brief as everyone dispersed for dinner. What Meadows and fellow researchers Giada Arney, Edward Schwieterman and Rodrigo Luger are doing is to produce computer models through which they can study Proxima b's habitability, based on everything from the planet's orbit to the characteristics of not just its host star, but the nearby stars Centauri A and B. Out of this come conclusions about...

I have much more to say about the Breakthrough Starshot meetings, but last evening I decided to slow the pace a bit. I mentioned in my first report that the discovery of a planet around Proxima Centauri had woven through our San Francisco meetings, creating a bright thread of discussion that continued through all three days. We are also getting papers on Proxima’s planet that inform us more about its potential habitability. In the next couple of days, then, I want to go through some of these before returning soon to the broader issues of Starshot. I also have to admit that I am still transcribing some of my handwritten notes from San Francisco to get everything in synch with my laptop, a process that is taking longer than I intended, thanks to my murky handwriting... In any case, whether Proxima b is habitable or not would surely play a large role in any decisions about using it as Starshot’s initial target. So let’s remember what Guillem Anglada-Escudé and the Pale Red Dot team had...

A planet in the habitable zone around Proxima Centauri? The prospect dazzles the imagination, but then, I’ve been thinking about just that kind of planet for most of my life. Proxima Centauri is, after all, the closest star to our own, about 15000 AU from the primary Alpha Centauri stars (though thought to be moving with that system). A dim red dwarf, Proxima wasn’t discovered until 1915, but it quickly seized the imagination of science fiction writers who pondered what might exist around such a star. Murray Leinster’s story “Proxima Centauri” (1935) is a clanking, thudding tale but it still evokes a bit of the magic of one of the earliest fictional interstellar voyages. Image: This wide-field image shows the Milky Way stretching across the southern sky. The beautiful Carina Nebula (NGC 3372) is seen at the right of the image glowing in red. It is within this spiral arm of our Milky Way that the bright star cluster NGC 3603 resides. At the centre of the image is the constellation of...