The Habitability of Planets Orbiting M-dwarf Stars

摘要

The prospects for the habitability of M-dwarf planets have long been debated,due to key differences between the unique stellar and planetary environmentsaround these low-mass stars, as compared to hotter, more luminous Sun-likestars. Over the past decade, significant progress has been made by both space-and ground-based observatories to measure the likelihood of small planets toorbit in the habitable zones of M-dwarf stars. We now know that most M dwarfsare hosts to closely-packed planetary systems characterized by a paucity ofJupiter-mass planets and the presence of multiple rocky planets, with roughly athird of these rocky M-dwarf planets orbiting within the habitable zone, wherethey have the potential to support liquid water on their surfaces. Theoreticalstudies have also quantified the effect on climate and habitability of theinteraction between the spectral energy distribution of M-dwarf stars and theatmospheres and surfaces of their planets. These and other recent results fillin knowledge gaps that existed at the time of the previous overview paperspublished nearly a decade ago by Tarter et al. (2007) and Scalo et al. (2007).In this review we provide a comprehensive picture of the current knowledge ofM-dwarf planet occurrence and habitability based on work done in this area overthe past decade, and summarize future directions planned in this quicklyevolving field.