Exobiology was the original term given to the sciences central to the question of life-in-the-Universe. It’s now been largely replaced by Astrobiology, but I’ll stick with the original. To investigate life-in-the-Universe one needs to look at what the most likely sort of extraterrestrial life will be. If Earth is any guide, the Universe will be full of LGM – not Little Green Men but Little Green Microbes. That’s because microbial life is probably very common throughout the cosmos, can adapt to a wide range of habitats, and is easily spread.
On Earth, microbes rule, OK? The biomass of all the bacteria, etc. put together easily equals the biomass of every other multicellular plant and animal put together. And microbes can live in environments where multicellular critters often can’t: from the coldest terrestrial environments, up to near boiling temperatures; from deep, deep underground to the heights of the atmosphere; from inside water-cooled nuclear reactors and the interior of rocks; to intensely saline, acidic and alkaline environments; to ecosystems where the Sun never shines. There are micro critters that can live off arsenic and thrive in toxic waste dumps!
You, and especially your insides, like your highly acidic stomach, play host to millions of bacteria – fortunately, most are beneficial.
They can even survive outer space. Bacteria survived on the surface of the Moon – on Surveyor Three. This was possibly the most significant discovery of the entire Apollo Moon program and it hardly even rated a mention. Astronauts from the Apollo 12 mission brought back to Earth parts of the unmanned Surveyor Three Lunar Lander. Terrestrial bacteria on those parts survived the lunar vacuum, solar radiations (ultraviolet rays, etc.), the massive temperature extremes, and lack of water and nutrients. Experiments since then in low earth orbit have confirmed that given just minimal shielding, bacteria can boldly go!
You’d be aware of how difficult it is to totally sterilize something, be it hospital equipment or a spacecraft bound for a Martian landing. They’re tough – have you ever read about a mass extinction event where a bacterial species went poof? Microbes are easy to transport. They can be blasted off the surface of the Earth, shielded from radiation by the debris, and survive to land on another world and be fruitful and multiply. There’s little doubt that somewhere way out there, terrestrial bacteria have hitched a ride to the stars, bolding going where lots of microbes have gone before!
Whether transported from Earth or otherwise, the massive range of exotic and extreme terrestrial habitats inhabited by microbes uncovered in just the past several decades, have open up a whole new frontier of possible extraterrestrial environments that might now be bio-friendly, where previously they had been written off as theoretically lifeless.
For example, no biological scientist would have given any credence several generations ago to the likelihood that terrestrial life could exist without the Sun as the ultimate energy source. Then the remarkable discovery of hydrothermal vent communities existing at the bottom of the oceans in darkness where the ultimate energy source was volcanic heat and the organisms thrived off of chemicals spewed out by those undersea volcanos. If the Sun were to go kaput tomorrow, humans would shortly follow suit. But the hydrothermal vent communities would keep on ticking.
That discovery opened up the possibility that various icy satellites of Jupiter and Saturn, though frozen solid at the surface, actually had liquid oceans beneath that solid surface, the heat generated by tidal pushing and pulling forces between the satellite and the parent planet melting the subsurface ice. Where there’s liquid water, there’s always the potential for life.
Translated, I firmly expect that the Universe is teaming with life in all sorts of places. The less than glamorous catch is that LGM is not going to stand for Little Green Men, but Little Green Microbes.
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