Copied from Poul Anderson Appreciation, 21 Nov 2013.
When Poul Anderson's There Life On Other Worlds?
(New York, 1963) was published, it was known that there were
extra-Solar planets sixteen times as massive as Jupiter. The size of
superjovians would vary from just sub-stellar to just super-Jovian.
Superjovians
that had formed either before or outside of metal-rich galactic regions
would be solid hydrogen with enormous hydrogen-helium atmospheres. If
superjovians, like the large Solar planets, rotate fast, then they are
flattened at the poles. Although massive, they might be no bigger than
Uranus because gravity should compress their cores, reducing even the
size of their atoms. They can be closer to their suns than Jupiter
because, if the latter were too close, then Solar heat would boil away
its hydrogen.
Hydrogen and helium would fatally dilute
any prebiological compounds, like methane or ammonia, in a superjovian
atmosphere. However, multiple star systems can contain superjovians
whose moons could be big enough to be terrestroid. Thus, although
terrestroid planets are unlikely either to form or to retain stable
orbits in a multiple system, terrestroid moons might, and since:
"Probably more than half the stars are double or triple..." (p. 86)
Anderson
argues that this capacity of superjovians to support terrrestroid moons
in multiple star systems significantly increases the likelihood of
life. I had known that terrestroid planets were unlikely to form or to
survive in multiple systems but not that terrestroid moons could do so.
Thus, this fact, highlighted by Anderson, is indeed significant.
Further, Hal Clement suggests fictionally in Mission Of Gravity that oil- or fat-based life might exist in liquid methane on superjovians.
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