Newsgroups: sci.space.science
Subject: Re: Jupiter and Europa: Life and Water...
From: Henry Spencer <henry@zoo.toronto.edu>
Date: Sat, 14 Jun 1997 03:24:10 GMT

In article <01bc75e1$bc0707c0$03d4f5cf@nexus-6>,
Mystery Girl <mystery@sentex.net> wrote:
>I thought the newest evidence showed Jupiter to contain MUCH less water
>than expected - almost none...

The spot where the Galileo probe went down had very little water vapor.
However, it is now clear that the probe had the bad luck to hit a highly
atypical part of Jupiter's atmosphere.  It's a great pity that Galileo
wasn't a paired mission like the Vikings and Voyagers; as it is, people
will be arguing for a long time about how to relate the Galileo probe data
to the *average* Jovian conditions.

Can you get such large differences in composition out of mere atmospheric
circulation?  You bet your booties you can.  If you sampled Earth's
tropical stratosphere, you'd think Earth couldn't have much water either.
The tropical stratosphere has *several orders of magnitude* less water
than the troposphere only a few kilometers below it... even though the
average air motion there is upward!  (The secret is that the tropopause,
which separates the two, is awesomely cold -- the graph of air temperature
versus altitude absolutely falls off a cliff as you hit the top of the
troposphere, especially in the tropics -- and all repeat *all* of the
water vapor which gets carried upward freezes out and falls away before
reaching the stratosphere.)

>better bet for finding life would be under the ice crust of Europa if there
>happens to be liquid water down there and the equivalent of the underwater
>geothermal vents ("black smokers") that are the basis of chemosynthetic
>food chains here on Earth...

There's another interesting and perhaps relevant fact that you left out.
The molecular biologists have been redrawing the family tree of Earth life
in recent years; if you want to know how closely related two organisms
are, genetic sequencing is a much more reliable way of finding out than
traditional methods based on superficial similarities.  And if you look
for modern organisms closest to the root of the tree -- the ones most
similar to the ancestors of all Earthly life -- what you find are the
heat-loving microorganisms, many of them with anaerobic chemical-based
metabolisms, like the ones found in the geothermal vents...
--
Committees do harm merely by existing.             |       Henry Spencer
                           -- Freeman Dyson        |   henry@zoo.toronto.edu