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rfmcdonaldProxima Centauri is the star other than the Sun nearest to us, a mere 4.2 light years away. The star is also commonly known as Alpha Centauri C, for the majority of recent studies suggest that Proxima is bound in a distant orbit a half-million years long around the A-B pair. A and B are Sun-like stars; Proxima, in contrast, is a dim red dwarf, with a total luminosity fractions of a percentage of Sol's even when it flares.
Centauri Dreams has made a couple of posts about Proxima. In the post yesterday, Paul Gilster discusses the nature of Proxima's orbit around A-B, and the apparently emerging consensus that Proxima does orbit the A-B pair in a distant orbit. If Proxima is gravitationally bound, this has implications for potential life on planets orbiting either star.
What of planets orbiting Proxima Centauri itself? No planets have been definitively sighted in orbit of Proxima, but the state of the astronomical art does set upper limits on the worlds that could orbit it.
Might an Earth-mass planet orbit Proxima in the habitable zone? Sure, but it would be exposed to flares, great upsurges of radiation that would complicate life.
More, doubtless, to come.
Centauri Dreams has made a couple of posts about Proxima. In the post yesterday, Paul Gilster discusses the nature of Proxima's orbit around A-B, and the apparently emerging consensus that Proxima does orbit the A-B pair in a distant orbit. If Proxima is gravitationally bound, this has implications for potential life on planets orbiting either star.
Given our age estimates of these stars, that would mean Proxima has orbited Centauri A and B roughly 6500 times. Its presence, note Laughlin and Wertheimer, introduces a mechanism for dislodging comets from outer orbits and pushing them into the inner system(s), allowing for the water they might otherwise lack. Even in terms of astrobiology, then, Proxima Centauri may play a role in making planets around Centauri A and B interesting, not to mention what it offers up in its own right.
What of planets orbiting Proxima Centauri itself? No planets have been definitively sighted in orbit of Proxima, but the state of the astronomical art does set upper limits on the worlds that could orbit it.
p[A] planet larger than Neptune could conceivably still be there around Proxima Centauri, but the odds do not favor it. We also learn from Endl and Kürster that no super-Earths have been detected larger than about 8.5 Earth masses in orbits with a period of less than 100 days. As for the habitable zone of this star — thought to be 0.022 to 0.054 AU, which corresponds to an orbital period ranging from 3.6 to 13.8 days — we can rule out super-Earths of 2-3 Earth masses in circular orbits. Here we pause again: The authors stress that their mass limits apply only to planets in circular orbits. Planets above these mass thresholds could still exist on eccentric orbits around this star.
So no planets yet around Proxima Centauri, and we’re beginning to rule out entire categories of planet here. We also have the possibility of smaller worlds in interesting orbits. The encouraging thing is that the radial velocity work on Proxima is getting better and better, and the authors see us closing in on planets of Earth size[.]
Might an Earth-mass planet orbit Proxima in the habitable zone? Sure, but it would be exposed to flares, great upsurges of radiation that would complicate life.
More, doubtless, to come.
