Williams D M, Kasting J F, Wade R A
Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park 16802, USA.
Nature. 1997 Jan 16;385(6613):234-6. doi: 10.1038/385234a0.
Possible planetary objects have now been discovered orbiting nine different main-sequence stars. These companion objects (some of which might actually be brown dwarfs) all have a mass at least half that of Jupiter, and are therefore unlikely to be hospitable to Earth-like life: jovian planets and brown dwarfs support neither a solid nor a liquid surface near which organisms might dwell. Here we argue that rocky moons orbiting these companions could be habitable if the planet-moon system orbits the parent star within the so-called 'habitable zone', where life-supporting liquid water could be present. The companions to the stars 16 Cygni B and 47 Ursae Majoris might satisfy this criterion. Such a moon would, however, need to be large enough (>0.12 Earth masses) to retain a substantial and long-lived atmosphere, and would also need to possess a strong magnetic field in order to prevent its atmosphere from being sputtered away by the constant bombardment of energetic ions from the planet's magnetosphere.
目前已发现可能的行星天体围绕九颗不同的主序星运行。这些伴星天体（其中一些可能实际上是褐矮星）的质量都至少是木星质量的一半，因此不太可能适宜类地生命生存：气态巨行星和褐矮星既没有可供生物栖息的固体表面，也没有液体表面。我们在此论证，如果行星 - 卫星系统在所谓的“宜居带”内围绕母恒星运行，那么围绕这些伴星运行的岩石卫星可能适宜居住，在宜居带中可能存在支持生命的液态水。天鹅座16B和大熊座47的伴星可能满足这一标准。然而，这样的卫星需要足够大（大于0.12个地球质量）以保留大量且长期存在的大气层，并且还需要拥有强大的磁场，以防止其大气层被来自行星磁层的高能离子持续轰击而溅射掉。
