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 also needs to look for life within our own solar system, apart from Earth of course. Take Mars, fourth rock from the Sun. There is (microbial) life on Mars. Microbial life on the Red Planet Mars is just about a sure fire a thing as death and taxes, albeit it’s probably spread very thinly.
Firstly, the two Viking landers, equipped with three separate life detection experimental techniques, all scored positive hits. It was only because the detection of organic molecules proved negative that it was thought prudent to look at exotic inorganic soil chemistry as an alternative explanation for the positive life detection results. There are those scientists involved with those Viking experiments who still maintain that microbial life was detected on Mars in 1976. Certainly it’s not 100% proof, but it’s certainly a pro-life run on the scoreboard.
Secondly, there is the evidence from the Martian meteorite found in the Antarctic (ALH 84001). Recall there was four separate and independent reasons for coming to the conclusion that the meteorite contained fossil microbial life forms from Mars. While each apart could have a non-biological explanation, the four together were highly suggestive of microbial life on Mars. Make that two runs on the scoreboard.
Thirdly, spacecraft orbiting Mars have detected methane in the Martian atmosphere. Methane is chemically reactive, and would disappear in short time frames were it not replenished by some source. A major source of methane on Earth is from microorganisms. While there are non-living sources of methane (volcanic activity), lack of such activity on Mars suggests that one chalk up yet another run on the board for life.
Fourthly, there’s no longer any question about Mars once having had extensive water. Spirit and Opportunity have settled that chestnut, and that’s quite apart from the visual evidence of what look like water channels, etc. on the Martian surface. Where’s there water, there’s the probability of life.
Lastly, it’s obvious that Earth and Mars would have exchanged materials via rocks being impacted off one planet and arriving on the other (so called ‘ballistic panspermia’). Since microbial life exists on Earth, some of it would have been transported throughout geological history to Mars. It’s quite possible that Mars seeded Earth as well, maybe even initially. Perhaps we are the Martians! And of course, it’s probable that both Mars and Earth were seeded from another outside source. That, IMHO, settles that.
Further readings:
DiGregorio, Barry E. & Levin, Gilbert V. & Straat, Patricia Ann; Mars: The Living Planet; Frog, Ltd., Berkeley , California
Goldsmith, Donald; The Hunt for Life on Mars; Dutton , New York
Sawyer, Kathy; The Rock from Mars: A Detective Story on Two Planets; Random House, New York
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