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Revisiting the Rare Earth Hypothesis: Insights on Life Beyond Our Planet

This paper reexamines the Rare Earth hypothesis, originally posited by Ward and Brownlee, through a critical lens. It explores why Earth might be a rare haven for complex life, considering factors like the Moon's presence, Jupiter's role, magnetosphere effects, and the implications of plate tectonics and water availability. The study delves into the historical events that shaped life on Earth and acknowledges the potential for simple life to be common, while complex, technological civilizations remain exceedingly rare. It also addresses the ongoing search for habitable exoplanets and the practical challenges of interstellar communication.

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Revisiting the Rare Earth Hypothesis: Insights on Life Beyond Our Planet

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  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.

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