We have applied these concepts to Gl 667C c, a ∼4.5 M Earth planet orbiting a 0.3 M Sun star at 0.12 AU. Planets orbiting stars with masses<0.3 M Sun may be in danger of desiccation via tidal heating. We simulated the evolution of hypothetical planetary systems in a quasi-continuous parameter distribution and found that we could constrain the history of the system by statistical arguments. However, these planets are not habitable, as past tidal heating desiccated them, and hence should not be ranked highly for detailed follow-up observations aimed at detecting biosignatures. Hence, some planets may form with large eccentricity, with its accompanying large tidal heating, and lose their water, but eventually settle into nearly circular orbits ( i.e., with negligible tidal heating) in the habitable zone (HZ). We call these planets “Tidal Venuses” and the phenomenon a “tidal greenhouse.” Tidal effects also circularize the orbit, which decreases tidal heating. Without hydrogen, the planet no longer has water and cannot support life. Here, we show that terrestrial exoplanets orbiting low-mass stars may be tidally heated at high-enough levels to induce a runaway greenhouse for a long-enough duration for all the hydrogen to escape. Traditionally, stellar radiation has been the only heat source considered capable of determining global climate on long timescales.
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