New Paper Explores The Prospects For Life Around M-Class Stars (arxiv.org)

Long-time Slashdot reader RockDoctor summarizes the significance of a new paper describing "The Habitability of Planets Orbiting M-Dwarf Stars": Although Star Trek had a minor smattering of "M-class planets" -- a designation that tells one nothing of substance -- "M-class star" is a much more meaningful designation of color, with two size classes, the dwarfs and the red giants... an M-dwarf of 1/10 the mass of the Sun will burn for around 1000 times the time that the Sun does... Therefore, if humanity ever meets an alien species, the odds of them coming from an M-dwarf [system] are already high. If humanity ever meets an alien species that has been around a billion years longer than us and has technology we can't even dream of, then the odds of it coming from an M-dwarf are overwhelmingly high.
This new paper offers "a comprehensive picture of the current knowledge of M-dwarf planet occurrence and habitability," pointing out that most of these stars are apparently orbited by planets packed closely together, with "a paucity of Jupiter-mass planets and the presence of multiple rocky planets." And more importantly, roughly a third of those rocky planets are orbiting in a "habitable zone" -- far enough away from their stars to support liquid water.

Comments

Re:Not putting a spin on things

[RockDoctor]

These are matters that the paper discusses. It only takes a couple of hours to read the 44 pages.

Short version - some close-in planets will be tidally locked, but not necessarily all of them. And (as discussed), the fact that M-dwarfs covers more mass variation than the next three classes of stars combined (F-dwarfs, G-dwarfs like the Sun and K-dwarfs) so it would be safe to expect a considerable variation in the behaviour of planets around M-dwarfs.

Consider tidal locking in a system with an M-dwarf star, a "hot Jupiter" and our Planet of Interest (PoI). If in orbit around either the hot Jupiter or the star, the PoI might become locked. But with the three in relatively close interaction, the PoI could be disturbed between locking to one, or the other, or alternating, or spinning irregularly. Feel free to use a planet with an irregular - literally chaotic, even - rotation in an SF scenario of your choice.

Re:Ummm, OK...

[RockDoctor]

you need a few star lifetime iterations to produce enough "metals" (for astronomers anything above hellium is a metal) for life to be viable.

This is probably true. But those stellar generations are not the generations of common stars (dwarf stars, up to, for example, the Sun's mass), but the lifetime of larger, faster evolving stars. You don't get metals further up the periodic table than carbon from a Sun-mass star. The lifetimes of such stars (say, more than 3 Sun masses ; I forget where the exact dividing line is for stars getting up to burning silicon to iron. It's somewhere near that mass.) is much shorter - more like a half billion years, The time for the ejecta from a supernova to become incorporated into the next generation of stars is more significant than the lifetime of the stars.

Interestingly, there is a fair correlation between the metallicity of a host star and it hosting a "super-Jupiter," but that correlation breaks down for smaller (Neptune-size and Earth-size) planets. While they still form around stars with a solar-similar metallicity on average, they're not more common around higher metallicity. That's odd. There's something going on there that works against the obvious expectation of how things go. I don't know about you, but I'd take that as a sign to pay more attention to observational data than theory.

they have other problems that are harmful to life in our sense

The study was (as is normal) carried out with the assumption of the stability zone of liquid water as the criterion for "habitable zone". No other constraint. You might be interested in finding something that would find William Shatner attractive - even if only as food - but that's not the only thing "life" could plausibly mean. A prokaryote-grade of organism with a non-nucleic acid genetic system would be far more interesting than something that beat Shatner at chess with an RNA-world type genetic system.