Paul Gilster announced a hiatus last month at Centauri Dreams, excepting visitors, but the proprietor seems to be back on a near-daily schedule lately. Last week he posted speculation about land or water Earthlikes... and yesterday he stuck an asterisk by the M-dwarf planets up to half solar M☉. UPDATE 10/11 - and now this.
The former presentation by Tilman Spohn and Dennis Hoening was looking at 80% land planets (like Aldiss' failing New Earth) and 20% watery, the latter of which they break out 1 Earthlike : 19 full water or worse. I'm in the "Worse!!" category on account visible "earthlikes" in the HZ could well be postNeptunian migrates from the Ceres belt - tiny rocky cores surrounded by many kilometers of water and steam. Keep in mind we won't get a density reading from an invisible Earthlike.
An important factor to remember about M-dwarf planets in their habitable zone is that they're ribbon worlds, also known as eyeballs. They are sure to be tidally-locked. Wikipedia tells me we have to upgrade to K 0.5-0.8 M☉ before a planet might get away with Mercurylike orbits UPDATE 10/8 and they're not habitable either. Of course at that distance around a smaller-disc star we cannot count on transits thus the concentration on M's.
M-dwarf planets often do transit for us. Per Tadahiro Kimura and Masahiro Ikoma in the latter-cited paper, 5% to 10% of these eyeballs should have water sufficient for us to observe it - through blue diffraction at the edges of the disc, for a start, but more from spectral-lines. But as is so-often noted, ribbonworlds will own solid land. Ice mainly; on the far side from their sun.
It's telling that the latter was supposed to be good news against earlier estimates for M systems, which - we may assume - were worse than what Spohn and Hoening are promising.
UPDATE 10/20: TRAPPIST 1e is too hot. Well yeah: we knew that. The point is to quell speculation on Proxima.
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