To: dietz@cs.rochester.edu (Paul Dietz) Cc: Fcc: sent Subject: Life on Jupiter (was: Re: SETI) In-Reply-To: Your message of 19 Aug 88 11:41:57 PDT <1988Aug19.144157.9490@cs.rochester.edu> ------- [Someone:] Jupiter cannot be left out [from the list of planets that may harbor life]. At some altitudes, the atmosphere is much the same as Earth's. [Paul F. Dietz:] At high pressure and temperature, hydrogen reacts exothermically with organic compounds to form methane, ammonia and water. Vertical circulation in Jupiter's atmosphere carries any given parcel downward to great depth every few days or so. It is unlikely that life could have originated or could survive there. I would not bet on it either, but... Imagine a small semi-solid particle floating in Jupiter's atmosphere, on the ascending side of a convection cell, at the altitude where liquid Water condenses out. Imagine that the particle consists of a Cheese core surrounded by a Glue solution. (Please substitute your favorite substances for Water, Cheese, and Glue, and your favorite gas giant for Jupiter.) If the particle is too light, it will be lifted to cooler altitudes, gain more Water by condensation, and become heavier. Conversely, if the particle is too heavy, it will sink, get hotter, lose some Water by evaporation, and become lighter. Conceivably, a particle whose dry weight falls in some relatively broad range will be able to hover indefinitely at a more or less constant altitude. Of course, this assumes the circulation pattern is reasonably stable. Modest changes in the speed of rising air can be compensated for by the same mechanism: a stronger/weaker updraft will only shift the equilibrium point to higher/lower altitudes. Lateral drift may be a problem, but if the equilibrium altitude lies somewhat below the center of the convection cell, I believe that the horizontal component of the air flow will tend to push the particle towards the center of the rising column. Particles outside this range will eventually fall or be carried down to the very hot levels where the Cheese and Glue are vaporized. Even if particles of the right size are rare to begin with, they will be naturally selected for, and with time their numbers may grow by many orders of magnitude. The result would be a relatively stable cloud of relatively uniform particles, somewhere along the lower part of every rising column. I may be wrong, but I belive this is the same mechanism that creates the sharply defined, flat-bottomed cumulus clouds here on Earth. In our turbulent atmosphere, the convection cells change constantly, and therefore our cumulus clouds have lifetimes measured in hours. In contrast, Jupiter's convection cells last for hundreds of years (Thousands? Millions? Billions?). So, unless the convection cells are too turbulent on a small scale, it may be possible for a sizable population of Wet Sticky Cheese particles to survive indefinitely as cumulus-like clouds in Jupiter's atmosphere. If such particles survived long enough, perhaps life could spontaneously evolve on them. Natural selection would favor particles whose composition provides better altitude feedback, so certain "weird" droplets that _a priori_ would seem highly improbable may actually become quite common. Furthermore, any particle able to "reproduce" --- i.e., able to somehow promote the formation of similar particles --- would eventually dominate its cloud. Even if the Wet Sticky Cheese particles survive only for a few thousand years, we shouldn't rule out the possibility of life evolving on them. We still haven't got the foggiest idea of how long it took to go from Earth's primordial soup to something that could pass for life; and even if we did, there is no reason to believe that the answer would be in any way relevant to the situation on Jupiter. Even if life cannot evolve on such particles, it may still be able to survive there once it has ben seeded from the outside. (For example, microscopic lifeforms evolved on Europa could have been lifted by meteorite impacts and rained onto Jupiter's Cheese clouds.) The moral of the story is that Life may have more aces up its sleeve than we can imagine, and we shouldn't be too quick to dismiss planets as "too hostile". In my opinion, the tropical region of the Moon is the only solid place off the Earth where we there is persuasive scientific evidence for the lack of life. Everywhere else the question is still wide open. Jorge Stolfi @ DEC Systems Research Center stolfi@src.dec.com, ...!decwrl!stolfi DISCLAIMER: The above opinions are not the sort of stuff my employer, my teachers, my friends, or my mother would like to be associated with. One problem >In temperature and pressure yes, but the composition is radically >different. Jupiter's atmosphere is "reducing", consisting mostly of >hydrogen, water, methane, and ammonia. Earth's atmosphere is >"oxidizing", as we all know. > >Being reducing doesn't mean Jupiter's atmosphere cannot contain life; >on the contrary, it may be better for life than Earth's because the >poison gas oxygen is not present. At high pressure and temperature, hydrogen reacts exothermically with organic compounds to form methane, ammonia and water. Vertical circulation in Jupiter's atmosphere carries any given parcel downward to great depth every few days or so. It is unlikely that life could have originated or could survive there.