Earth-scale planets in the classical habitable zone (HZ) are more likely tobe habitable if they possess active geophysics. Without a constant internalenergy source, planets cool as they age, eventually terminating tectonicactivity and rendering the planet sterile to life. However, for planetsorbiting low-mass stars, the presence of an outer companion could generateenough tidal heat in the HZ planet to prevent such cooling. The range of massand orbital parameters for the companion that give adequate long-term heatingof the inner HZ planet, while avoiding very early total desiccation, isprobably substantial. We locate the ideal location for the outer of a pair ofplanets, under the assumption that the inner planet has the same incident fluxas Earth, orbiting example stars: a generic late M dwarf ($T_{eff}=2670 K$) andthe M9V/L0 dwarf DEN1048. Thus discoveries of Earth-scale planets in the HZzone of old small stars should be followed by searches for outer companionplanets that might be essential for current habitability.
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机译：如果拥有活跃的地球物理学，则在经典可居住区（HZ）中的地球尺度行星更可能是可居住的。如果没有恒定的内部能源，行星会随着年龄的增长而冷却，最终终止构造活动，并使行星失去生命。但是，对于低质量恒星的行星吸附来说，外部伴星的存在会在HZ行星中产生足够的潮热，以防止这种冷却。伴星的质量和轨道参数范围很广，可以给内部HZ行星提供足够的长期加热，同时又避免非常早的完全干燥。我们假设一对行星外部的理想位置，假设内部行星具有与地球相同的入射通量，围绕示例恒星运行：一个普通的后期M矮星（$ T_ {eff} = 2670 K $）和M9V / L0小矮人DEN1048。因此，在发现老小恒星高地带的地球规模的行星之后，应该寻找可能对当前宜居性至关重要的外部伴星。
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