[ExI] Life must be everywhere!

Anders Sandberg anders at aleph.se
Sun Apr 15 07:06:09 UTC 2012

It is worth considering how efficient different biospheres are at 
distributing potentially life-bearing ejecta.

The heavier the planet the more likely and energetic impacts are, but 
they tend to be more denaturating, have atmospheres slowing particles 
down and the escape velocity is higher. Small worlds like Europa might 
have frozen life in their ice crust that are easily chipped away by 
small impacts - and despite orbiting heavy Jupiter Europa is pretty high 
up in the solar s6ystem gravity well (see http://xkcd.com/681_large/ - 
much more trustworthy than Wikipedia :-) ) And of course, smaller worlds 
are likely to be more common too. Places like Ceres are also more likely 
to be hit than planets and moons in more upscale neighborhoods.

It would be fun to calculate this. Sounds like a good research paper, if 
it doesn't exist.

I suspect the emission rate varies by at least two orders of magnitude, 
perhaps much more. Once life spreads through a solar system in a 
panspermia model I suspect that the spore production becomes dominated 
by the most efficient emitter, no matter where life originated. So we 
should not obsess over whether Earth-originating spores can reach the 
stars, but rather whether Earth can seed Europa and Europa can seed the 

(And, remember, if panspermia turns out to be true, then the risk of the 
Great Filter being in our future goes up a lot! Panspermia is not good 
news for us. )

Anders Sandberg
Future of Humanity Institute
Oxford University

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