Tarter Jill C, Backus Peter R, Mancinelli Rocco L, Aurnou Jonathan M, Backman Dana E, Basri Gibor S, Boss Alan P, Clarke Andrew, Deming Drake, Doyle Laurance R, Feigelson Eric D, Freund Friedmann, Grinspoon David H, Haberle Robert M, Hauck Steven A, Heath Martin J, Henry Todd J, Hollingsworth Jeffery L, Joshi Manoj M, Kilston Steven, Liu Michael C, Meikle Eric, Reid I Neill, Rothschild Lynn J, Scalo John, Segura Antigona, Tang Carol M, Tiedje James M, Turnbull Margaret C, Walkowicz Lucianne M, Weber Arthur L, Young Richard E
SETI Institute, Mountain View, California 94043, USA.
Astrobiology. 2007 Feb;7(1):30-65. doi: 10.1089/ast.2006.0124.
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.
稳定的、进行氢燃烧的M型矮星约占银河系中所有恒星的75%。它们寿命极长，而且由于其质量比太阳小得多（在0.5至0.08个太阳质量之间），其温度和恒星光度较低，且峰值在红色波段。我们重新审视了目前已知的关于在M型矮星附近的经典液态地表水宜居带内形成或迁移到该区域的类地行星的可能性。对原行星盘的观测表明，行星形成物质在M型矮星周围很常见，但N体模拟在估计位于其宜居带内的潜在宜居、有水行星的可能性时存在差异，其宜居带宽度仅约为G型恒星宜居带宽度的五分之一至五十分之一。特别是鉴于有声称探测到质量小至5.5和7.5个地球质量的行星围绕M型恒星运行，似乎没有理由排除类地行星存在的可能性。在狭窄宜居带内的潮汐锁定同步自转不一定会导致大气坍塌，而且活跃的恒星耀斑可能并不像以前认为的那样是一个在进化上不利的因素。我们得出结论，M型矮星确实可能是生命起源和演化可能发生的行星的可行宿主。一些行星过程，如地热活动的停止或热和非热大气损失过程，可能会将行星宜居期限制在远短于M型矮星极端寿命的时期。然而，将M型矮星纳入旨在寻找宜居世界和生命证据的计划是有意义的。本文介绍了由美国国家航空航天局天体生物学研究所赞助并在SETI研究所召开的一次跨学科研讨会（http://mstars.seti.org）的总结结论。
