Thursday, 21 November 2013

Superjovian Planets

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. 

1 comment:

Sean M. Brooks said...

Hi, Paul!

And we both know Poul Anderson's novel VIRGIN PLANET has a roughly Earth sized moon of a super jovian which was terrestroid and became the home of stranded colonists from Earth.