Not that we have ever been confirmed as finding a single live cell anywhere but planet Earth but, as ScienceDaily explains:
Planets cool as they age. Over time their molten cores solidify and inner heat-generating activity dwindles, becoming less able to keep the world habitable by regulating carbon dioxide to prevent runaway heating or cooling.
But astronomers at the University of Washington and the University of Arizona have found that for certain planets about the size of our own, the gravitational pull of an outer companion planet could generate enough heat — through a process called tidal heating — to effectively prevent that internal cooling, and extend the inner world’s chance at hosting life.
The outer planet is necessary, Barnes added, to keep the potentially habitable planet’s orbit noncircular. When a planet’s orbit is circular, the gravitational pull from its host star is constant, so its shape never changes, and there is no tidal heating.
And so, the researchers conclude, any discoveries of Earth-sized planets in the habitable zone of old, small stars should be followed by searches for outer companion planets that might improve the inner world’s chance at hosting life. More.
Based on our present experience, wouldn’t a large moon do just as well? Maybe we should discuss that more.
We actually don’t even know how life got started on Earth. See The Science Fictions series at your fingertips (origin of life) for a quick. handy guide to why.
Abstract Earth-scale planets in the classical habitable zone (HZ) are more likely to be habitable if they possess active geophysics. Without a constant internal energy source, planets cool as they age, eventually terminating tectonic activity. Planets orbiting low-mass stars can be very old, due to the longevity of such stars, so they may be rendered sterile to life in this way. However, the presence of an outer companion could generate enough tidal heat in the HZ planet to prevent such cooling. The range of mass and orbital parameters for the companion that give adequate long-term heating of the inner HZ planet, while avoiding very early total desiccation, is probably substantial. We locate the ideal location for the outer of a pair of planets, under the assumption that the inner planet has the same incident flux as Earth, orbiting example stars: a generic late M dwarf (Teff = 2670?K) and the M9V/L0 dwarf DEN1048. Thus discoveries of Earth-scale planets in the HZ zone of old small stars should be followed by searches for outer companion planets that might be essential for current habitability. – C. Van Laerhoven, R. Barnes, R. Greenberg. Tides, planetary companions, and habitability: habitability in the habitable zone of low-mass stars. Monthly Notices of the Royal Astronomical Society, 2014; 441 (3): 1888 DOI: 10.1093/mnras/stu685
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