The “Rare Earth” Hypothesis Revisited

1. The “Rare Earth” HypothesisRevisited Joe Gale The Hebrew University of Jerusalem ILASOL December 2012

2. (Springer Verlag – 2000)

3. Ward and Brownlee – their main contentions - and critique Why Rare?Why Not! Presence of : Moon - not necessarily unique Jupiter - protective effect exaggerated Magnetosphere - “ “ “ Plate tectonics - probably not unique or necessary Water - probably common 2/3 of star systems are double or triple. Planet orbits (hence climates would be erratic) - even one third of all stars is a huge number. Special Events in History of Complex Life: e.g. Cambrian “explosion”. - no reason to think that such Demise of Dinosaurs events would not occur allowing dominance of mammals. Simple life possible, Complex life - number of planets in “nearby” Extremely unlikely regions of galaxy is enormous

4. See Oded Avraham, ILASOL 2012 Mercury – may have ice at poles Venus Ancient life?? Subsurface oceans Complex Life?? Atmosphere of Venus Planet Earth - to same scale Methane / Ethane on surface. Possible subsurface liquid water. Possible Life “Niches” in the extraterrestrial Solar System

5. Kepler space Telescope(searching for extra-Solar System planets) - Launched 2009 - Studies – 145,000 “nearby” stars (~500 ly) - Detects eclipse of star by planet, when in line with Earth. - Alignment chance (Earth, planet, star) 1/215 Planets detected ( to Nov. ‘12) - 2,326 Of these: 207 Earth Size, 48 in Habitable Zones 2 orbiting Sun-like stars (Note: Earth based telescopes continue to discover planets by radial velocity perturbations of central star. e.g. an Earth size planet orbiting Alpha Centauri B.- about 3.5ly distant; a star with a surface temperature of ~5200 K) -

6. Radiation as a function of Black Body Temperature (Wien’s Law) Waveband of Oxygenic Photosynthesis Note: Sun’s surface temperature ~ 5,800oK Red Dwarf stars (about 70% of Milky Way galaxy) ~ 4000oK

7. Caveat emptor(beware before you buy) We are limited by Astrobiology’s working hypothesis: “Life elsewhere will be similar to that on Earth”. One example of problematics: Newly found planets orbiting Red Dwarf stars, in their Habitable Zones, will receive low quantum energy photon radiation which cannot drive earth-like photosynthesis! (So, no life?!). However, there may be non Earth-like photosynthesis, operating with low energy photons at wavelengths > 800nm (< 720 nm is required to split water molecule). (So, Non-Earthlike life may be supported?!).

8. Ernst Mayr’s argument against the chance of another Technological Civilization (from C.Sagan-E.Mayr debate. Updated-2012) (Today Archaea are added). i.e. just once in the 13.75 By universe.

9. The Science Fiction Dream

10. Can we send probes or spaceships to the newly found Earth-like planets, or communicate with any advanced civilization detected? Given: A planet orbiting a “nearby” Sun-like star, at a distance of 100 ly. A probe or space ship able to accelerate to an average speed of one tenth the speed of light. (Possible, but vastly faster than todays space probes/ships). Human lifetime ~ 100 y; a generation time of ~ 30 y. Then: Transit time to target – 1,000 years = 10 lifetimes or 30 generations. – not feasible - Signal (EMR) exchange with another civilization = 200 years (and they probably don’t speak English!). - Problems of energy would also prohibit transmission of signals to such distances. If there is another civilization capable of overcoming such problems: they would probably put us in a zoo (if we are so lucky!).

11. Conclusion – Ward and Brownlee were essentially correct – Earth is Rare! (probably) - Simple Life – may be common (but still unproven, except on Earth).- Complex life, certainly technological civilizations – probably extremely rare.Moreover:- Close-up study of extra Solar Systems having Life clement conditions, And/Or two way Communication with another Civilization – are not presently feasible.