SETI Re: Sagan: Life on Europa info


Robert Owen (rowen@technologist.com)
Tue, 28 Sep 1999 14:26:29 -0400


Larry Klaes wrote:

> >From: "Bruce Moomaw" <moomaw@jps.net>
> >To: "Icepick Europa Mailing List" <europa@klx.com>
> >Subject: Weekend update
> >Date: Mon, 27 Sep 1999 18:11:56 -0700
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> >Sender: owner-europa@klx.com
> >Reply-To: europa@klx.com
> >
> >
> > Now for the good news: The abstracts from this December's American
> >Geophysical Union meeting are available
> > http://submissions3.agu.org/PublicSearch/SearchAbstracts.asp ), and they
> >are full of fascinating stuff. For us, most of it is in Special Sessions
> >B10 (Deep Biospheres), B14 (Astrobiology) and P5 (Compositions of the
> >Surfaces of the Icy Galilean Satellites). The papers in the Deep Biospheres
> >session make it clear that biologists are now certain that there is a
> >downright thriving bacterial ecosystem at astonishing depths in the Earth --
> >and that they are increasingly optimistic about the implications of this for
> >present-day life on (or rather, in) both Mars and Europa. Stephen Clifford,
> >in "The Subsurface Hydrosphere of Mars", says: "The comparative isolation
> >and stability of this subpermafrost [region of subsurface liquid water]
> >makes it difficult to imagine how life, once established in this niche,
> >could become extinct." Several other writers say that the evidence
> >continues to grow that such deep subsurface microbes were among the earliest
> >forms of life to evolve on Earth, and maybe the very earliest -- which
> >presumably means that they would have been among the earliest to appear on
> >Mars. Jack D. Farmer, in "Exploring for Evidence of Martian Life in Polar
> >Ice Deposits", says that hot-spring activity may have spat some of these
> >microbes all the way up to the Martian surface, and that they may still be
> >very well preserved in some near-surface ground ice deposits in the polar
> >regions.
> > As for Europa, the most interesting papers are three in Session B14
> >and one in P5 (John F. Cooper's "Energetic Ion and Electron Irradiation of
> >the Icy Galilean Satellites:, which agrees with Chris Chyba's recent
> >Division of Planetary Sciences paper that "Downward transport of [chemicals
> >produced by Jupiter's radiation in Europa's surface ice], driven by tidal
> >stresses and thermal instabilities on timescales of 10 million to 1 billion
> >years, could deliver significant chemical energy and other astrobiological
> >resources to subsurface ocean environments.") The B14 papers are:
> > (1) Richard Greenberg's "Habitability of Europa's Crust", in which
> >he says that areas where liquid water from Europa's ocean has gushed to near
> >the surface, instead of carrying useful chemicals back down to the ocean,
> >may instead carry oceanic microbes up to necessary "oxidants which are
> >available only near the surface."
> > (2) Thomas M. McCollom's "The Potential for Biomass Production by
> >Autotrophic Methanogenesis at Hydrothermal Systems on Europa and the Early
> >Earth", in which he confirms that the maximum mass of Europan organisms that
> >could possibly be supported by the chemicals produced by seafloor
> >volcanic-vent activity is only 1/10,000 that of Earth's biosphere -- but
> >also says that methane production from such vents on Europa may be much
> >higher than that of Earth's vents, and that in fact "Under some plausible
> >conditions, the amount of energy available from methanogenesis may be
> >equivalent to that available from the largest energy source in terran
> >systems" -- namely, the oxidation of hydrogen sulfide by oxygen produced by
> >photosynthetic Earth plants and dissolved in our oceans. Since, on Earth,
> >the mass of bacteria produced around vents by the latter process is high
> >enough to support thriving colonies of large animals, it seems to me that he
> >is hinting that for the first time there is some chance that Europan vents
> >might -- just might -- be able to support multicelled Europan animals.
> > (3) William B. McKinnon's "On the Conditions Necessary for a
> >Thriving Chemoautotrophic Ecosystem on Europa", in which he gives reasons
> >for thinking that Europan "volcanism is plausible", and disagrees with Eric
> >Gaidos' recent piece in "Science" (which I described in a June "SpaceDaily"
> >piece) predicting that the rocks of Europa's mantle are so depleted in
> >oxygen that they spew forth no significant amount of carbon dioxide, sulfur
> >dioxide or elemental sulfur to provide Europan germs with an energy source.
> >(McKinnon points out that Io -- which is probably internally similar to
> >Europa in composition -- spews large amounts of sulfur dioxide and elemental
> >sulfur from its volcanoes, indicating that its interior is highly oxidized.)
> >And since McCollom's paper says that Gaidos is right in saying that Europa's
> >vents spew forth large amounts of methane instead, but says that he's wrong
> >in thinking that such vents could not support large amounts of microbes, we
> >may have a win-win situation in the question of whether volcanic vents on
> >Europa (assuming they exist in adequate numbers) do supply chemicals capable
> >of supporting fairly large amounts of microbes.
> >
> > Bruce Moomaw
> >
> >
> >==

=======================
Robert M. Owen
Director
The Orion Institute
57 W. Morgan Street
Brevard, NC 28712-3659 USA
=======================



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