Habitability of terrestrial-mass planets in the HZ of M Dwarfs – I. H/He-dominated atmospheres
Habitability of terrestrial-mass planets in the HZ of M Dwarfs – I. H/He-dominated atmospheres
复制标题
M 矮星 HZ 中类地质量行星的宜居性 – I. H/He 主导的大气层
DOI：
--
复制
发表时间：
2016
期刊：
影响因子：
--
通讯作者：
S. Mohanty
中科院分区：
文献类型：
--
作者：
J. Owen;S. Mohanty
M矮星的普遍存在，加上相对容易探测到它们周围的地球质量行星，使它们成为寻找和描述“可居住区”（HZ）行星的主要目标。然而，开普勒发现，地球质量的系外行星通常具有大量的H/He包层，包括质量分数（$M_{env}/M_{core}$）$\gtrsim 1$%。如果这些行星在Gyr时间尺度上保持这样的包络，即使在HZ内，它们也不会“适合居住”。由于M矮星的X射线/紫外线通量很强，我们研究是否有足够的包络质量可以被光蒸发掉，使这些行星变得适合居住。我们改进了以前的工作，通过使用流体动力学模型，占辐射冷却以及从流体动力学到弹道逃逸的过渡。采用模板活性M矮星XUV光谱，包括恒星演化，并考虑蒸发和热演化，我们表明：（1）质量损失是（相当）低于以前的估计，使用“能量有限”的形式主义，并忽略了过渡到金斯逃逸，（2）在HZ的内边缘，行星的核心质量$\lesssim 0.9$ M$_\oplus$，（3）在HZ的外缘，蒸发不能去除1%H/He包层，即使从核芯到0.8M +$，也不能去除1%H/He包层。因此，如果行星形成时有庞大的H/He包层，那么只有那些具有低质量核心的行星最终可能适合居住。核心$\gtrsim $1 M$_加上$，与$\gtrsim $1%的纳塔尔H/He信封，将不适合居住在H Z的M矮星。
The ubiquity of M dwarfs, combined with the relative ease of detecting terrestrial-mass planets around them, has made them prime targets for finding and characterising planets in the "Habitable Zone" (HZ). However, Kepler finds that terrestrial-mass exoplanets are often born with voluminous H/He envelopes, comprising mass-fractions ($M_{env}/M_{core}$) $\gtrsim 1$%. If these planets retain such envelopes over Gyr timescales, they will not be "habitable" even within the HZ. Given the strong X-ray/UV fluxes of M dwarfs, we study whether sufficient envelope mass can be photoevaporated away for these planets to become habitable. We improve upon previous work by using hydrodynamic models that account for radiative cooling as well as the transition from hydrodynamic to ballistic escape. Adopting a template active M dwarf XUV spectrum, including stellar evolution, and considering both evaporation and thermal evolution, we show that: (1) the mass-loss is (considerably) lower than previous estimates that use an "energy-limited" formalism and ignore the transition to Jeans escape, (2) at the inner edge of the HZ, planets with core mass $\lesssim 0.9$ M$_\oplus$, can lose enough H/He to become habitable if their initial envelope mass-fraction is $\sim$1%, (3) at the outer edge of the HZ, evaporation cannot remove a $\sim$1% H/He envelope even from cores down to 0.8 M$_\oplus$. Thus, if planets form with bulky H/He envelopes, only those with low-mass cores may eventually be habitable. Cores $\gtrsim$ 1 M$_\oplus$, with $\gtrsim$1% natal H/He envelopes, will not be habitable in the HZ of M dwarfs.
DOI：
10.1088/0004-637x/800/2/135
发表时间：
2014-12
期刊：
The Astrophysical Journal
影响因子：
--
作者：
C. Dressing;D. Charbonneau;X. Dumusque;S. Gettel;F. Pepe;A. Collier Cameron;D. Latham;E. Molinari;S. Udry;L. Affer;A. Bonomo;L. Buchhave;R. Cosentino;P. Figueira;A. Fiorenzano;A. Harutyunyan;R. Haywood;J. Johnson;M. López-Morales;C. Lovis;L. Malavolta;M. Mayor;G. Micela;F. Motalebi;V. Nascimbeni;D. Phillips;G. Piotto;D. Pollacco;D. Queloz;K. Rice;D. Sasselov;D. Ségransan;A. Sozzetti;A. Szentgyorgyi;C. Watson
通讯作者：
C. Dressing;D. Charbonneau;X. Dumusque;S. Gettel;F. Pepe;A. Collier Cameron;D. Latham;E. Molinari;S. Udry;L. Affer;A. Bonomo;L. Buchhave;R. Cosentino;P. Figueira;A. Fiorenzano;A. Harutyunyan;R. Haywood;J. Johnson;M. López-Morales;C. Lovis;L. Malavolta;M. Mayor;G. Micela;F. Motalebi;V. Nascimbeni;D. Phillips;G. Piotto;D. Pollacco;D. Queloz;K. Rice;D. Sasselov;D. Ségransan;A. Sozzetti;A. Szentgyorgyi;C. Watson