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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.
Our water and atmosphere were burned away when the Earth was still forming. We got them back from comet impact.
Not only that, but shallow Earth-like oceans are likely better for life than deep Europa-like oceans. Although we may think of Earth as a watery planet, water is far more rare on Earth than in the rest of the Universe, making up only 0.02% of Earth's mass. If our oceans were as deep as Europa's, the continents would be completely submerged, there would be no upwelling, and all the nutrients would settle at the bottom, 100km below the surface. Without nutrients, the sunlit surface would be nearly lifeless. There might be some life around volcanic vents, but those are too rare to provide much scope for evolution. Mostly likely, if there was life at all, it would never even become multi-cellular. Having your oceans boiled away is a good thing!
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.
Presumptuous maybe, but TFA is flawed as hell; planets move after they have formed, and generally inwards. They make no mention of this fact anywhere.
In our case, we had the Jupiter - Saturn duo that stabilized things, and prevented Jupiter from crashing into the Sun, taking the inner 4 planets with it.
It's entirely plausible that decent planets with atmospheres exist within the habitable zones of small stars, with crazy shit like 50 day years, and the dark side of the moon melts a little when it swings close to the sun. Heh.
But, a planet that formed close in to a star early on, and has remained there the whole time the system has cooled down, is likely to be a barren rock. Agreed. And a bit obvious...