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A Reappraisal of the Habitability of Planets Around M Dwarf Stars

机译:重新评估M个矮星周围的行星的可居住性

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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 geother mal 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.
机译:稳定的,燃烧氢的M矮星约占银河系中所有恒星的75%。它们的寿命极长,并且由于它们的质量比太阳小得多(介于0.5和0.08 M_(Sun)之间),因此它们的温度和恒星发光度较低,并以红色达到峰值。我们重新审视了目前有关在M矮星附近的经典液面水可居住区域内形成或迁入该行星的潜在可能性的已知信息。对原行星盘的观察表明,行星构造材料在M矮星附近很普遍,但N体模拟对它们居住在其宜居区域内的潜在宜居性湿行星的可能性的估计有所不同,其大约只有五分之一至一G星宽度的/ 50倍。尤其是根据所声称的探测到的质量分别小于5.5和7.5 M_(地球)绕M恒星运行的行星,似乎没有理由排除地面行星的可能性。在狭窄的可居住区域内,潮汐锁定的同步旋转并不一定会导致大气塌陷,而活跃的恒星爆发可能并没有像以前想象的那样对进化不利。我们得出的结论是,矮矮星可能确实是行星的可行宿主,在行星上可以发生生命的起源和进化。许多行星活动,例如停止地热活动或热和非热大气损失过程,可能会将行星可居住性的持续时间限制在比M矮星的极端寿命短得多的时期内。尽管如此,将M矮星包括在旨在寻找宜居世界和生命证据的程序中还是有道理的。本文介绍了由NASA天体生物学研究所赞助并在SETI研究所召开的跨学科研讨会(http://mstars.seti.org)的总结性结论。

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