Gonna try to stay focused here at #SoCIA18 with "The Value of Astrobiology with or without Specimens" by Gonzalo Munevar. What can this discipline tell us, even if we never find ETlife?
Ex: Earth life favors left-handed amino acids, right-handed sugars. Are these accidents of evolution, or are there reasons? Why does DNA use only 4 bases? Why do proteins use 20 amino acids? All these would be addressed by even N=2 origins of life.
ETlife would have evolved under different history, geology, accidents (meteorite strikes etc), so alien road to complexity would be different from ours.
Well, if we fail to find organic evolution (despite expecting/predicting some), we may learn about our failed reasoning about origin of life. And pursuit of astrobiology is entwined with our understanding of extraterrestrial geologies.
Compare to ALH84001, that Martian meteorite found in 1984, where in 1996 David McKay at NASA claimed it had evidence of life (wormlike structures, globules of various hydrocarbons & sulfides). But other scientists disagreed.
One main reason why McKay's conclusions rejected: all of the compounds/structures could be produced by inorganic processes. Occam's Razor, let's not jump to the extraordinary conclusion (Martian life). Plus, the "wormlike structures" ~1/50 size of Earth bacteria.
However, there are counterarguments. Forex, the magnetite in the sample is extremely pure - on Earth only bacteria produce it so pure. Found bacterialike structures, typical bacterial food, typical bacteria excreta - all in close proximity. &more.
Controversy spurred interest in possibility of very small bacteria on Earth. And eventually located! In 2015 found ultra-small bacteria around the size of larger "Martian Wormlike Structures," and sequenced genome.
Primitive RNA bacteria could indeed be small enough to match those MWS. So at least one of our Rejection Criteria was wrong. Maybe we were too hasty... but more importantly, our rejection of Mars Life Data led to new discoveries on Earth!
That said, "Pooping Magnetite" is the name our new glam-punk band and/or interior design aesthetic.
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