THE SEARCH FOR LIFE ELSEWHERE

1. SAGAN AND THE SEARCH FOR LIFE ELSEWHERE

• -Carl's lifelong passion; Everything else was context. Sagan first paper
• -My personal association with Carl began in 1960--the very beginning.
• -Let's contrast views in 1960 to present
• -But first, "What controls distribution of life?"

  2. LIQUID WATER AND THE GOLDILOCKS PRINCIPLE

  3. VENUS?

• -1960, Liquid water still possible, but unlikely in view of high radio brightness.
• -Sagan thesis (1960) and other research pointed to "Unearthly" high surface temperatures.
• -Mariner 2 (1962) and Ground-based radio observations confirmed
• -Mariner 5 and Venera 4 (1967) proved conclusively.

  4. MARS?

• -1960, high expectations for simple plant life:
  • -Lowell's Legacy
  • -Coincidence of spin rate, obliquity, polar caps, and seasonal markings
  • -Sinton bands in 1956, 1960 -- Chlorophyll?
• -Mariner 4 (1965). Lunar-like surface, surface pressure ~0.5 % of Earth
• -Mariners 6/7 (1969) Solid Carbon Dioxide seasonal frost, not water; Liquid water not stable on Mars' surface! Sagan Dust Hypothesis for markings (1967)
• -Mariner 9 (1971-72) Ancient catastrophic flood channels; an aqueous past!
• -Life could have existed billions of years ago--Why not now? Sagan Papers
• -Viking 1,2 (1976-78) No organic material at all in soil; surface reacts chemically with Viking's aqueous reagents.
• -Mars' surface is self-sterilizing! Life cannot exist on surface.
• -No life or organic remnants possible on surface now or for long time in past.
• -Allen Hills meteorite issue (1996). Microbial life widespread within Earth's crust; Certainly possible at Mars billions of years ago. Why not now?
• -But very difficult to test that hypothesis.

  5. ELSEWHERE IN THIS SOLAR SYSTEM?

• -Giant Planets--no liquid water regimes. Sagan Jupiter speculations.
• -Satellites? In 1960 just spots on photographic plates.
  • Voyager 2 (1979) showed Titan far too cold for liquid water
  • Voyagers (1979), Galileo (1997) provide strong indirect evidence for liquid water ocean on Europa below surface ice layer.

  6. OTHER SOLAR SYSTEMS?

• -1960 view-- Planets are rare. The product of a chance passage of two stars was a common view
• -Therefore, life very rare...maybe even unique ...was also common view.
• -Earth, and its intelligent life, probably a scientific "miracle"
• -1962-1980. Human and spacecraft exploration of Moon and Terrestrial Planets show that Earth formed naturally from Solar System environment and dynamical state; nothing "miraculous". Life also seems to have arisen naturally from earth's setting. Thus, ancient microbial life, at least, may have formed elsewhere at an earlier epoch when environmental conditions were more hospitable, e.g. Mars.
• -Cautionary Note!! Still no plausible explanation of first step from "broth" to self-replicating organisms. Potential Paradigm Shift.
• -1992 on. Discovery of big planets orbiting other stars at unexpected locations. Planets are more common than had been anticipated by analogy with this solar system.
• -Cautionary Note!! This may be evidence that WE are the oddball, not the norm. Therefore, perhaps habitable planets are very rare after all.

  7. SETI--THE GREATEST SEARCH OF ALL

• -Fundamental question--"Are We Alone in Universe?" (Sagan and Shklovsky (1966)
• -Testable Hypothesis-- "There are technically advanced civilizations maintaining radio or other "beacons" for us to detect and initiate communication".
• -Observational Challenge: Where to point?, How strong a Signal?, What frequency?, What modulation? Thus, one must assume most of parameters and search some limited phase space.
• -Common Search Assumptions:
• -"magic" frequencies.
• -V. narrow CW or v. short pulse modulation.
• -Targetted vs. Sky Survey Approaches
• -Congressional Failure of Nerve (1981,1993)

  8. THE FUTURE: CARL SAGAN'S LEGACY

• -Complete search for habitable environments in this Solar System:
• -Subsurface of Mars and Europa.
• -Complete search for preserved evidence of ancient life on Mars.
• -Inventory planetary bodies orbiting nearby stars.
• -Identify Earth-like planets and search for spectral indicators of life.
• -Expand SETI to Earth orbit for submillimeter and shorter searches