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The “Rare Earth” Hypothesis
Revisited
Joe Gale
The Hebrew University of Jerusalem
ILASOL December 2012
(Springer Verlag – 2000)
Ward and Brownlee – their main
contentions - and critique
Why Rare?
Presence of :
- Moon
- Jupiter
- Magnetosphere
- Plate tectonics
- Water
- 2/3 of star systems are double or triple.
Planet orbits (hence climates would be erratic)
Special Events in History of Complex Life:
e.g. Cambrian “explosion”.
Demise of Dinosaurs
allowing dominance of
mammals.
Simple life possible, Complex life
Extremely unlikely
Why Not!
- not necessarily unique
- protective effect exaggerated
“
“
“
- probably not unique or necessary
- probably common
- even one third of all stars is a
huge number.
- no reason to think that such
events would not occur
- number of planets in “nearby”
regions of galaxy is enormous
Venus
Mercury – may have ice at poles
See Oded Avraham, ILASOL 2012
Ancient life??
Atmosphere of
Venus
Subsurface oceans
Complex Life??
Planet Earth
- to same scale
Methane / Ethane
on surface. Possible
subsurface liquid water.
Possible Life “Niches” in the extraterrestrial Solar System
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)
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
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?!).
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.
The Science Fiction Dream
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!).
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.