Were Carl Sagan and Edwin Salpeter right? In 1976 they suggested that the warm layers of Jupiter’s hydrogen/helium outer layers of gas could be home to huge living “…gas-filled balloons…”, sinkers, and hunters. Is there enough methan there to act as a carbon source? Isn’t it a bit windy up there? Where is life going to get a foothold . . .er . . . balloon hold to get started?
Where the atmosphere is at a comfortable room temperature, there is a pressure ten times higher than Earth’s at sea level, and the radiation is horrendous. The better news is that there are hydrocarbons beneath the ammonia clouds. However, there is so little water that any life would likely be based on something else.
Solvents are to be expected in order to allow the self-organization of huge molecules that can do the energetic reactions needed to power life, even the kind of simple life that started it all on Earth—the algae. (Recently, it has been discovered that we are built under the direction of ancient genes we inherited from the algae. Nature has a way of “not fixin’ what ain’t broke.”)
The problems with Jupiter are its horrendous forces. We’ve mentioned too much atmospheric pressure, radiation, and too little water. Add to that the fact that the planet is rotating at a nasty speed of 110 meters per second. It puts out hurricanes like the Great Red Spot, which is so large it could swallow several Earths. Its lovely zones and belts move in opposite directions, adding to its nasty history.
The planet’s history is simply implausible as a life startup, with its rapid transition from extreme cold in a vacuum to extreme heat in high pressure. It provided a habitat with no place to land and collect its hydrocarbon bits into something we could call life. Other chemical possibilities are not promising.
Considering other gas giants in our solar system—Saturn isn’t much better that Jupiter, but Neptune and Uranus offer a bit more hope with their larger concentration of methane (providing a nice blue look). Ammonia and water form a distinct smoggy layer, but the small quantities of water and oxygen are probably the game changers there.
Energy sources on all of our gas giants are available. They include solar radiation and heat at various altitudes, high pressure, and the kinetic energy of the high winds, which blow at higher speeds than our cyclones in the upper atmospheres.
There may be more hope for gas giants in other solar systems. We are finding out there “. . . chemical precursors for biomolecules. . . “ (See Cosmic Biology by Irwin and Schulz-Makuch. www.abebooks.com/book-search/title/cosmic-biology/free-shipping/page-1/) Also, there are comfortable temperatures and pressures formacromolecular biology , in addition to enough water to get life going.
Of course life may be nothing like the life we know, for many of the gas giants of exoplanets are very different from ours. Some are much larger or too close to their suns, but some may be closer to planets in habitable zones so that panspermia becomes an option. Meanwhile, it looks as if the more interesting possibilities for life could be out there and not on the gas giants here.