John C. Mather
Senior Project Scientist: James Webb Space Telescope (JWST)
Nobel Prize: Physics (2006): Cosmic Microwave Background Anisotropy and Spectrum
Senior Scientist: NASA’s Goddard Space Flight Center
Author: The Very First Light (w/John Boslough, 2009, Basic Books)

How will humanity first discover ET Life?
Best guess: Biosignatures
2 key observations so far:
Life on Earth occurred very soon (hundreds of millions of years) 
after the oceans occurred, but our civilization took 3.5 billions of years longer
Earth-size temperate planets are very common, 10-20% of G, K, and M stars have them
Conclusion: Life is a thermodynamic imperative, not a rare coincidence. 
Atoms are programmed to self-organize. Look wherever there are or were oceans! 
There are many places to look.

Where to look and why?

Close by: Mars; farther away, large moons of Jupiter and Saturn; perhaps, Venus had an ocean long ago before climate change
Advantage: our robots can visit, analyze, bring home samples for microscopic analysis (cell remnants), chemical analysis (biomolecules), isotopic analysis (fractionation due to biological processes)
Odds good, 50%? If having an ocean is enough.
Time frame: several decades, unless we’re very lucky
Farther away: exoplanets with signs of molecules out of chemical equilibrium, a sign of photosynthesis: H2O, O2, O3, CO2, CH4, etc. Examine with telescopes and spectroscopy.
Disadvantage: possible false positives; difficult to build equipment
Odds good, 50%? But evidence might not be convincing.
Time frame: several decades, unless we’re very lucky. (JWST might see water, probably not oxygen)
Much much farther away: signs of intelligent life	
Disadvantage: why would they send us a signal? What else would we look for?
Advantage: why not just look?
Odds extremely low: space is large, our time is short so far, ”their” time may be short (for example: subject to Malthusian food supply limits)
Time frame: very very long, the needle is in a very big haystack

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