Copied from Poul Anderson Appreciation, 22 Nov 2013.
The
subjovian planets, Uranus and Neptune, are intermediate in mass between
jovians and hypothetical superterrestrials. Not large enough to retain
jovian quantities of hydrogen or helium, they instead have stone and
metal cores, atmospheric methane and probably also solid ammonia. If
such a planet received more solar heat, either in a closer orbit or from
a hotter sun, then it would lose even more hydrogen and helium,
retaining an atmosphere of hydrogen, methane, ammonia and inert gasses.
Poul Anderson argues in Is there Life On Other Worlds?
(New York, 1963) that on such a planet, i.e., a hot subjovian, organic
compounds should form and become more complex although the remaining
excess of hydrogen would prevent the formation of any cellular
chlorophyll plus which, if any oxygen were released, then it would
combine with the hydrogen to form water, thus circumventing an
Earth-like plant-animal system - although not necessarily preventing the
evolution of other kinds of complex organisms. In fact, Anderson argues
later in the book that hydrogen-breathers are possible and even
probable.
It is important to read this passage carefully because its conclusion:
"...subjovians at reasonably high temperatures seem very likely to be inhabited..." (p. 87)
- refers
not, as I initially thought, to Uranus or Neptune, but instead to
hypothetical hotter subjovians in other planetary systems.
A superterrestrial:
would have higher gravity, therefore a thicker atmosphere with a stronger greenhouse effect;
thus, would be like Venus if near its sun but cooler further out;
should
in the latter case have photosynthesis and an oxygen-nitrogen
atmosphere but with more concentrated pre-biological matter leading to
faster evolution, also air that would both burn and poison human beings;
but, if smaller, might have habitable mountaintops, like Anderson's Rustum or Niven's Plateau.
(A
week away with only one Anderson book means not less blogging but more
blogging about a single text. However, this one nonfiction work contains
a lot of concentrated information.)
With my granddaughter, who is of Jewish descent through her father, I have just watched Fiddler On The Roof which ends with Russian Jews about to embark for New York where Anderson's works were published...
And now planets intermediate in size between earth & Uranus/Neptune turn out to be the common sort or extra-solar planet
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