Into the abyss

Sometimes it's good to just let go. In science this can mean taking a deep breath and getting wildly speculative - knowing that sometimes, just sometimes, wild speculation can be correct. I was asked a question yesterday about life in gas giant planets. This is far removed from the kind of humdrum stuff we deal with for terrestrial type planets, and definitely speculative, but like all good speculation it forces us to think hard about the details. It's not a new idea; in 1976 two formidable scientists, Sagan & Salpeter presented a serious look at the possibilities in their paper 'Particles, environments, and possible ecologies in the Jovian atmosphere'. The paper is wild, they even get into classification of hypothetical Jovian organisms, from 'sinkers', to 'floaters' and 'hunters' and the reproductive traits of said beasties. They got away with publishing this in a respectable journal by doing some more mundane stuff too, on the possible growth rate of particulate matter in Jupiter's atmosphere.

Many fascinating issues are raised. Since that work we now, thanks to the Galileo probe, have a much better - although still hugely incomplete - understanding of the chemistry of Jupiter's upper atmosphere. There is a pretty wide range of organic molecules, plus water (although less than we might have expected), and many are seen in abundances that indicate they have been pulled up from much deeper down in great convective updrafts. It's a somewhat messy environment. Wind speeds are huge compared to a terrestrial environment - persistent at a few hundred miles an hour - and there appear to be 10 planet encircling jet streams. Nonetheless, at depths where the pressure is about 10 times that here on Earth the temperature is in the regime that we ourselves bask in, and it's awfully tempting to think about what might be going on down there.

Is there any way to know if there is an abyssal biosphere on Jupiter without taking a dive to see? Life can certainly alter its environment, its metabolic processes can completely alter local chemical equilibria. Perhaps we could look for signs of chemical activity in the great upwelling clouds at Jupiter's surface, a natural dredging system. It'd be tough though - we first need to understand what the 'sterile' chemical equilibrium is of a planet like Jupiter, and we're not there yet. But suppose we do sort this out, then another intriguing and wildly speculative idea raises its head. We have got quite good at detecting molecules like water and methane in certain gas giant exoplanets, even noticing when the expected chemical equilibrium is not there (in Nature this week - planet GJ 436b may have a methane deficiency). Perhaps one day we might be so good at doing this that we could begin to search for signs of a deep, floaty, biosphere....