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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.
Earth has been advertising itself for more like a half-billion years. An atmosphere with free oxygen is rare, at least we haven't found one yet out of the explanets we've discovered. To be sure, we haven't studied the atmosphere on very many, but at the very least we know how to do so, at least for some.
There has been some suggestion of merely chemical processes that can give rise to free oxygen in the atmosphere, but I don't know how likely (or un) those processes are, and whether they cause the levels the Earth has, especially with traces of methane present at the same time.
We know our atmosphere has been biosculpted, and that would be something others could have seen for half a billion years.
One must assume that any alien civilization capable of interstellar travel would know at least as much as we do about the relevant technologies. That would include something Keplar-like, only better. You don't want to take your first interstellar steps to a place with no relevant planets.
The living have better things to do than to continue hating the dead.
Given that we have a sample size of one: The earth
I think it's a tad ridiculous that we assume we have any idea what kind of environment can support life at all. There is no environment that we've explored that we can rule out the existence of life on. Yes, I understand that's because we haven't really explored any of them... but that's kind of the point.
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.
Umm, it seems you're not aware that the prevailing theory is that those volcanic vents were the birthplace of life on Earth, and probably its primary residence for hundreds of millions of years thereafter? And that it's believed that the first light-sensitive molecules were probably used by microorganisms to flee the lethal ultraviolet sunlight penetrating the upper layers of the oceans? Until photosynthesis evolved sunlight had nothing to offer life: the energy gradients around volcanic vents were far more easily harnessed.
Even today it's believed that the vast mass of life on Earth are chemovores living deep underground, whose ancestors may have never seen sunlight in the entire history of the planet.
Even multicellular life thrives around those undersea vents, and quite possibly deep underground as well. The upper reaches of the ocean, to say nothing of the land, were barren energy-poor wastelands likely only colonized by those poor saps who couldn't compete for the more desirable locations.
--- Most topics have many sides worth arguing, allow me to take one opposite you.
Actually, given that there's 100-400 billion stars in the galaxy, and 0.001^4 works out to one in a trillion, that gives you about a 10 to 40% chance of there being one intelligent species in the milky way. /semantic
But I agree, in general. The odds of earth being the only planet with life at all in the whole galaxy...are pretty astronomical, in my opinion.
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...
Ok, I understand that, but isn't it possible for an ice bearing comet (or several) to impact the planet at some later time when the sun was cooler? Surely those planetary systems have their own equivalent of oort clouds?
The whole reason that a red dwarf is so dangerous to live around is its low gravity. It can hurl flares from its surface that ascend far out into space and reach its tight little "habitable zone", and its planets will occasionally orbit through a flare and get zapped. The flares are channeled and accelerated by electromagnetic turbulence that originates from deep inside the star. Even after the surface temperature of its photosphere finally declines, the star will continue to flare until it shrinks down to a white dwarf (which has no habitable zone at all, since its starlight is extreme ultraviolet radiation that can easily blast water molecules apart). Since M-class stars typically have expected lifetimes of trillions of years, you'd have to wait a long time to see it happen.