A reappraisal of the habitability of planets around M dwarf stars.
Stable, hydrogen-burning, M dwarf stars make up 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 M(Sun)), 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 that reside within their habitable zones, which are only about one-fifth to 1/50th 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 M(Earth) orbiting M stars, there seems no reason to exclude the possibility of terrestrial planets. Tidally locked synchronous rotation within the narrow habitable zone does not 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 nonthermal 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. This paper presents the summary conclusions of an interdisciplinary workshop (http://mstars.seti.org) sponsored by the NASA Astrobiology Institute and convened at the SETI Institute.
Tarter
Jill C
JC
SETI Institute, Mountain View, California 94043, USA. tarter@seti.org
Backus
Peter R
PR
Mancinelli
Rocco L
RL
Aurnou
Jonathan M
JM
Backman
Dana E
DE
Basri
Gibor S
GS
Boss
Alan P
AP
Clarke
Andrew
A
Deming
Drake
D
Doyle
Laurance R
LR
Feigelson
Eric D
ED
Freund
Friedmann
F
Grinspoon
David H
DH
Haberle
Robert M
RM
Hauck
Steven A
SA
Heath
Martin J
MJ
Henry
Todd J
TJ
Hollingsworth
Jeffery L
JL
Joshi
Manoj M
MM
Kilston
Steven
S
Liu
Michael C
MC
Meikle
Eric
E
Reid
I Neill
IN
Rothschild
Lynn J
LJ
Scalo
John
J
Segura
Antigona
A
Tang
Carol M
CM
Tiedje
James M
JM
Turnbull
Margaret C
MC
Walkowicz
Lucianne M
LM
Weber
Arthur L
AL
Young
Richard E
RE
D055580:Astronomical Phenomena; D001256:Astronomy; D017753:Ecosystem; D018559:Exobiology; D005118:Extraterrestrial Environment; D000069497:Origin of Life; D016083:Planets