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.
3 comments:
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.
Sean
"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."
Really?
IINM it was a reasonable belief, but the objects in that size range thought to exist, eg: the one that inspired Mesklin, turned out to not exist.
"Probably more than half the stars are double or triple..." (p. 86)
Apparently since Anderson wrote that, it was found that most *large* stars are double or triple, but stars from the sun size on down are more likely to be single. The difficulty of detecting red dwarfs skewed the statistics.
Whether planets orbiting red dwarfs can be habitable, is a major question affecting how common life is in the universe.
Kaor, Jim!
And that reminds me of how I read of Anderson declining to have IS THERE LIFE ON OTHER WORLDS? republished in the 1980's or '90's because there were so many advances in astronomy since 1963 that the book was outdated. Any revision of IS THERE... would need to be so drastic that it would be better to write a completely new book on the topics it discussed. And I wish Anderson had done that!
But, as long as such caveats are kept in mind, IS THERE LIFE ON OTHER WORLDS? is very much worth reading.
Anderson's book can be supplemented by reading other works in the same field: CONTACT WITH ALIEN CIVILIZATIONS (2010), by Michael A.G. Michaud; or INTELLIGENT LIFE IN THE UNIVERSE? (2005), by Brother Guy Consolmagno, SJ.
Ad astra! Sean
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