In our never-ending quest for Vulcans, Hynerians and little green men, we’ve blasted off satellites to the far reaches of our galaxy to scope out evidence of extraterrestrials. Now research has suggested that these so-called aliens are most likely microbial — and dead.
Astronomers can see the logic behind all the hypothesizing about alien life. "The universe is probably filled with habitable planets, so many scientists think it should be teeming with aliens," acknowledges Dr. Aditya Chopra, professor at the Australian National University and co-author of "The Case for a Gaian Bottleneck: The Biology of Habitability," which was recently published in Astronomy. So why, then, are they making a case for most of that life being fossilized?
Exoplanets (planets that orbit other stars besides our sun) may have once been oases for a sort of primordial soup much like the one that spawned life on Earth. Unfortunately for anyone who dreams of being catapulted through space at warp 9 and beamed down to some advanced civilization light-years away, the cruel reality of space is that most habitable conditions don’t last. Surface temperature needs to be stable for billions of years if there is to be any hope of E.T. evolution. Without the precise balance of elements, greenhouse gases, water and albedo (the amount of light a planet’s surface can reflect), no life is able to thrive long enough to evolve, and the environments of most exoplanets are too volatile to maintain the magic ratio.
How did our planet do it? Earth was not too different from Venus and Mars during their first billion or so years orbiting the sun. This could mean that both now-uninhabitable zones could have possibly hosted ancient alien microbes. So why did Venus heat up into a swirling storm of poisonous gases and Mars freeze into a cosmic icebox?
Blame feedback loops -- i.e., when the output of a system on a planetary surface feeds back into that same system. Positive feedback ironically doesn’t bode well for potential life forms, because the loop keeps increasing instability in a planet’s motion, temperature and chemical composition as it feeds back into itself. Another culprit is thermal runaway. It’s a vicious cycle of increases or decreases in temperature that results from negative feedback loops, inevitably leads to temps further soaring or plummeting, and turns a once-habitable planet into a bacterial graveyard. Runaway heating and cooling means most exoplanets have their default setting on insta-burn or insta-freeze. Erratic conditions like this are the reason that life on many exoplanets, if there was ever life at all, has gone the way of the dinosaurs.
What makes Earth unique is that it was able to hold on to habitable conditions just long enough for emergent life to take hold. "Early life is fragile, so we believe it rarely evolves quickly enough to survive," says Chopra. Negative feedback loops, which keep reducing inconsistencies as they feed back into themselves, stabilized conditions on the nascent planet. Microbes were able to keep breeding until the surface was covered in bacterial mats much like those that spring up around heat vents on the ocean floor (the other final frontier). The metabolic reactions of these microbes were able to regulate greenhouse gas production, which in turn stabilized the atmosphere and kept their writhing masses alive. At some point those writhing masses became us.
Does this mean that we will only ever encounter alien life in galactic graveyards? Not necessarily. Satellites continue to probe an uncharted universe scattered with billions and billions of Carl Sagan’s pale blue dots. Planets that can maintain life are rare, but if one exists, there will always be believers. Any one of those pale blue dots could be pulsing with life.
(Source: Science Daily)