A Re-appraisal of the Habitability of Planets Around M Dwarf Stars

In this morning's astro-ph, an interesting paper (with a notable
s.a.seti co-author):

Title: A Re-appraisal of the Habitability of Planets Around M Dwarf Stars
Authors: Jill C. Tarter, Peter R. Backus, Rocco L. Mancinelli, Jonathan
M. Aurnou, Dana E. Backman, Gibor S. Basri, Alan P. Boss, Andrew
Clarke, Drake Deming, Laurance R. Doyle, Eric D. Feigelson, Friedmann
Freund, David H. Grinspoon, Robert M. Haberle, Steven A. Hauck II,
Martin J. Heath, Todd J. Henry, Jeffery L. Hollingsworth, Manoj
M. Joshi, Steven Kilston, Michael C. Liu, Eric Meikle, I. Neill Reid,
Lynn J. Rothschild, John M. Scalo, Antigona Segura, Carol M. Tang,
James M. Tiedje, Margaret C. Turnbull, Lucianne M. Walkowicz, Arthur
L. Weber, Richard E. Young
Comments: To be published in Astrobiology. 34 pages

Stable, hydrogen-burning, M dwarf stars comprise about 75% of all
stars in the Galaxy. They are extremely long-lived and because they
are much smaller in mass than the Sun (between 0.5 and 0.08 MSun),
their temperature and stellar luminosity are low and peaked in the
red. We have re-examined what is known at present about the potential
for a terrestrial planet forming within, or migrating into, the
classic liquid-surface-water habitable zone close to an M dwarf
star. Observations of protoplanetary disks suggest that
planet-building materials are common around M dwarfs, but N-body
simulations differ in their estimations of the likelihood of
potentially-habitable, wet planets residing within their habitable
zones, which are only ~ 1/5 to 1/50 of the width of that for a G
star. Particularly in light of the claimed detection of the planets
with masses as small as 5.5 and 7.5 MEarth orbiting M stars, there
seems no reason to exclude the possibility of terrestrial
planets. Tidally locked synchronous rotation within the narrow
habitable zone doesn't necessarily lead to atmospheric collapse, and
active stellar flaring may not be as much of an evolutionarily
disadvantageous factor as has previously been supposed. We conclude
that M dwarf stars may indeed be viable hosts for planets on which the
origin and evolution of life can occur. A number of planetary
processes such as cessation of geothermal activity, or thermal and
non-thermal atmospheric loss processes may limit the duration of
planetary habitability to periods far shorter than the extreme
lifetime of the M dwarf star. Nevertheless, it makes sense to include
M dwarf stars in programs that seek to find habitable worlds and
evidence of life.

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