X-Message-Number: 3310
Date: Thu, 20 Oct 1994 18:04:52 -0400 (EDT)
Subject: SCI.CRYONICS Life on Ice

Date sent:  20-OCT-1994 18:02:23 

Life on Ice

The Possibility of Life on Europa and Enceladus

Craig Levin

                           I: Introduction

     The search for extra-terrestrial life has been one of the major
driving forces of planetology. Many of planetology's major figures,
from Sir William Herschel, to Percival Lowell, even up to Carl Sagan,
have believed in a plurality of worlds. Yet, despite the optimism of
all the searchers, not one of the terrestrial planets have been found
to harbor life, save our own planet Earth.

     Yet the possibilities for life elsewhere in our Solar System have
been poorly explored. In the sixties, Carl Sagan postulated the
existence of life under and among Jupiter's clouds. Unfortunately, the
proposal seemed to lack merit when it came time to design Galileo's
atmospheric probe. However, it is not Jupiter, nor is it any of the
other Jovian planets that I believe to be the abode of fellow
creatures, but instead, two of the icemoons I wrote about in my March
1990 article in the EJASA entitled "Ice Moons of the Jovian Worlds":
Enceladus and Europa.

     In this article I will first describe what life need in order to
get started on a world. Next, I will desribe the conditions on Europa
and Enceladus in both the past and present. Finally, I will compare
the five described conditions, and thereby discover if, indeed,
Enceladus and Europa are harbors for life, or dead lumps of ices.

                 II: Conditions for the Birth of Life

     Life is a delicate thing, yet it arose on Earth under conditions
that might seem harsh to us here nearly three billion years after the
fact.  Earth's atmosphere was nothing then like it is now. Instead of
the familiar oxygen and nitrogen that we all breathe, Earth's
atmosphere was mainly composed of steam, carbon di-oxide, methane, and
ammonia.  Thanks to experiments made in 1953 by Stanley Miller, it has
been shown that if these chemicals are exposed to electric sparks or
ultra-violet light, most of the known amino acids and some of the
simpler proteins will form. In 1936, A.I. Oparin found that these
amino acids and protein would form globules in water. These he
believed were the progenitors of protozoa, the lowest forms of life.
Thus life was started on Earth. But what about the main
subjects-Enceladus and Europa?

           III: Primeval Conditions on Europa and Enceladus

     It has been shown that Jupiter and Saturn are both warmer now
than can be accounted for by solar radiation. It seems to be the
general consensus that this heat is the remnant of the original energy
that was the result of the respective planet's collapse into a dense
ball of rock, metal, and liquid metal hydrogen. If the heat is enough
to show up signifigantly now, what must it have been like four or five
billion yers ago? Terence Dickinson claims: "Near the origin of the
solar system [sic] Jupiter was more like a miniature sun than a
planet, shedding enough heat that... would have allowed [Europa's]
surface to be covered in an ocean..."{1} I am including Saturn in this
as well, in light of its similar size and composition.  During this
time, there also were other processes that could have given Enceladus
and Europa open oceans for the Sun to shine on: heat of accretion and
heat of differentiation could have had melted the crusts of both
moons.  Meteorite impacts could have opened pits in their icy crusts.
However, do the moons have organic material for the Sun's ultra-violet
rays to shine on?

     Let us look at the composition of the typical ice moon. In this
"typical" ice moon, we find, in addition to some rock and metal, water
ice, dry ice, and frozen ammonia and methane. Despite their frozen
state today, at the time, if water was in liquid form then, most, if
not all of the chemicals listed above were also in liquid or vapor
form. Plus, with the exposure of these vapors and liquids to the young
Sun's more energetic ultra-violet rays, life's components would have
formed on the far-off surfaces of Enceladus and Europa. But what of
the present day? How could protozoa formed then somehow survive to the

            IV: Present Conditions on Europa and Enceladus

     Protozoa on Earth seem to tolerate many different environments,
but one thing seems clear. All life needs water, and all life needs an
energy source, be it sunlight or plants or geothermal energy. Do the
present conditions on Europa and Enceladus give these conditions to
the hypothetical protozoa?

     I say yes. There is a good chance that both Europa and Enceladus
have liquid water under their ice crusts. The heat generated by tidal
interactions between Io, Europa and Jupiter, according to Lucchita and
Soderblom, was enough to melt the ice under the crust of Europa.
Enceladus has been observed to send out plumes of water by Voyager II.
So we can assume that at least there is water to sustain subterranean
life on the two moons. But is there an energy source? Considering that
most estimates of the thickness of Europa's crust, and it seems to be
the warmer of the two moons, being both larger and less cratered, lie
around a figure of twenty-five miles, I think one can rule out
sunlight as a source of energy. But geothermal energy on such active
moons is quite possible, to say the least. It has certainly been shown
on Earth that geothermal heat sources can sustain life.

                               V: Life?

     Let us compare the five conditions described above. For life's
founding, we need ammonia, methane, carbon di-oxide, steam, and either
lightning or ultra-violet rays. Europa and Enceladus had, and still
have, the chemicals necessary.  If one considers likely the scenario I
have described above for the Saturn and Jupiter, then ultra-violet
light was present as well.  Life had a good chance of starting.  For
life's continuance, we need an energy source and liquid water.  Due to
their tidal interactions with their neighbors, Enceladus and Europa
have liquid water and geothermal energy. This leads me to belive that
our first aliens are to be found as Europans and Enceladians, fellow
members of the Solar system of which we ourselves are a part.

{1} Terence Dickinson, _The Universe and Beyond_ (Camden East: Camden
House Publishing, Ltd., 1986), p. 54

                          List of References

Baugher, Joseph F.. _The Space-Age Solar System_. New York: John
Wiley and Sons, Inc., 1988.

Briggs, G.A. and F.W. Taylor. _The Cambridge Photographic Atlas of the
Planets_. New York: Cambridge University Press, 1988.

Dickinson, Terence. _The Universe and Beyond_. Camden East:
Camden House Publishing, Ltd., 1986.

Hartmann, William K.. _The Grand Tour_. Toronto: Saunders of
Toronto, Inc., 1981.

Hartmann, William K.. _Out of the Cradle_. New York:
Workman Publishing Company, Inc., 1984.

Morrison, David, ed. _Satellites of Jupiter_. Tucson: The
University of Arizona Press, 1982.


To Arthur Clarke, for inspiring in me the idea of life on Europa and
Enceladus from his book _2010_, and to John Novak, who helped find and
patch some holes of the first draft.


Craig Levin began to get involved in astronomy when, in second grade,
he received H.A. Rey's "Find the Constellations" as a birthday
present.  As a high school junior, he had his first article published
in the now-defunct Small Scope Observers' Association's newsletter,
and by his senior year in high school was helping to establish the
"Astronomical Newsletter", a now-defunct magazine based in Atlanta.
At present, he is a physics major at Bradley University who intends to 
turn his first love, planetology, into his profession.


Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=3310