Proxima's other planet

Hat-tip to the Morning Report: Mario Damasso is reinforcing his position that Proxima Centauri has a second, colder planet – “c” (“a” being the star, by convention). “c” swings around on a circular orbit of about five to five and a half of our years. Its minimum mass is about five Earths but, since it doesn’t transit relative to us, is at an angle to us; so like to be rather heavier than that. The planet isn't visible directly; these readings come from seventeen years observing the star, alongside our increasingly-accurate measurements and understanding of said star.

Wikipedia as of this morning still considers Damasso’s conclusion “unconfirmed” but the evidence keeps stacking to his favour. The ESA’s Gaia mission is slated to release a dataset, the “EDR3”, later this summer. That might clinch the proper motion of the star and, thereby, nail down the planets’ angles relative to us.

For this weak-gravity star, such a long-period planet orbits only 1.5 AU away from it. Here, it doesn’t get much insolation. Damasso’s team projects 30-50 K temperature. That is the temperature of Pluto and Triton. I’d up that a bit, because I expect this one has an envelope of methane and of other such “ices” – read, gasses – to a light-absorbent extent, like Neptune. I don’t expect it to be visible to our eyes out here - ever. But there is hope for infrared.

At this distance, minimum-mass, and circular orbit; and since there’s nothing special between it and Proxima b: planet c has room for direct satellites and, in its L4 and L5, for Trojans - like Neptune's. Hildas too.

FLIPAROUND 12/24/22 - The outer c is busted by a method applied successfully elsewhere. Instead is confirmed an inner c, named d at the time.