Europa's Ocean Contains Enough Oxygen to Support Life

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, 1-202-328-2010 x116.

October 8, 2009

Contacts:
Sanjay S. Limaye
DPS Press Officer
+1 608-262-9541


Prof. Richard Greenberg
University of Arizona

+1 520-904-9457 (cell, through Oct. 9)
+1 520-621-6940 (office)

VERTICAL TRANSPORT THROUGH EUROPA'S CRUST:
IMPLICATIONS FOR OXIDANT DELIVERY AND HABITABILITY

The global ocean on Jupiter's moon Europa contains about twice the
liquid water of all the Earth's oceans combined. New research suggests
that there may be plenty of oxygen available in that ocean to support
life, a hundred times more oxygen than previously estimated.

The chances for life there have been uncertain, because Europa's ocean
lies beneath several miles of ice, which separates it from the
production of oxygen at the surface by energetic charged particles
(similar to cosmic rays). Without oxygen, life could conceivably exist
at hot springs in the ocean floor using exotic metabolic chemistries,
based on sulfur or the production of methane. However, it is not
certain whether the ocean floor actually would provide the conditions
for such life.

Therefore a key question has been whether enough oxygen reaches the
ocean to support the oxygen-based metabolic process that is most
familiar to us. An answer comes from considering the young age of
Europa's surface. Its geology and the paucity of impact craters
suggests that the top of the ice is continually reformed such that the
current surface is only about 50 million years old, roughly 1% of the
age of the solar system.

Richard Greenberg of the University of Arizona has considered three
generic resurfacing processes: gradually laying fresh material on the
surface - opening cracks which fill with fresh ice from below - and
disrupting patches of surface in place and replacing them with fresh
material. Using estimates for the production of oxidizers at the
surface, he finds that the delivery rate into the ocean is so fast
that the oxygen concentration could exceed that of the Earth's oceans
in only a few million years. Greenberg presents his findings tomorrow
at the 41st meeting of the American Astronomical Society's Division
for Planetary Sciences now under way in Fajardo, Puerto Rico
(http://dps.aas.org/press).

Greenberg says that the concentrations of oxygen would be great enough
to support not only microorganisms, but also "macrofauna", that is,
more complex animal-like organisms which have greater oxygen demands.
The continual supply of oxygen could support roughly 3 billion
kilograms of macrofauna, assuming similar oxygen demands to
terrestrial fish.

The good news for the question of the origin of life is that there
would be a delay of a couple of billion years before the first surface
oxygen reached the ocean. Without that delay, the first pre-biotic
chemistry and the first primitive organic structures would be
disrupted by oxidation. Oxidation is a hazard unless organisms have
evolved protection from its damaging effects. A similar delay in the
production of oxygen on Earth was probably essential for allowing life
to get started here.

Richard Greenberg is the author of the recent book "Unmasking Europa:
The Search for Life on Jupiter's Ocean Moon", which offers a
comprehensive picture of Europa for the general reader.