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'Mirage Earth' Exoplanets May Have Burned Away Chances For Life
vinces99 writes: Planets orbiting close to low-mass stars — easily the most common stars in the universe — are prime targets in the search for extraterrestrial life. But new research led by an astronomy graduate student at the University of Washington indicates some such planets may have long since lost their chance at hosting life because of intense heat during their formative years. Low-mass stars, also called M dwarfs, are smaller than the sun, and also much less luminous, so their habitable zone tends to be fairly close in. The habitable zone is that swath of space that is just right to allow liquid water on an orbiting planet's surface, thus giving life a chance. [Researchers found] through computer simulations that some planets close to low-mass stars likely had their water and atmospheres burned away when they were still forming because they were exposed to high temperatures from their parent stars.
Or they evaporated and the gravity of the planet is strong enough to hold onto H2. Unlike Mars for instance.
Most likely it was a combination of heat and weaker gravity. The hotter the planet, the more gravity needed to hold onto an atmosphere, because the molecules move faster. The Earth's collision with Theia is believed to have generated enough heat to liquify the entire mass of the resulting combined planet. This would have been hot enough to drive off any water vapor in the atmosphere. One reason we believe this is true is the absence of much neon on Earth. Neon is abundant in the universe, but very rare on Earth. If the Earth was too hot to hold on to neon (mw=20) then it wouldn't have been able to hold onto water (mw=18) either.