Jupiter's moon Europa is flowing with a buried liquid water
ocean that contains much more oxygen than previously thought – enough to
possibly support life, scientists say.
There is no solid evidence of life for anywhere besides
Earth, but Europa has long been considered a good place to look for biological
activity.
Europa's ocean lies beneath several
miles of ice, so scientists wondered whether it has much oxygen, which is thought
to be created at the surface by interaction with energetic charged particles
from the sun. Scientists think oxygen is probably necessary for life's
metabolic processes, unless some creatures use exotic chemistry involving
sulfur or methane.
The global
ocean on Europa contains about twice the liquid water of all the Earth's
oceans combined. The new research suggests that there may be a hundred times
more oxygen than previously estimated.
To probe how much oxygen might lie in
the ocean, Richard Greenberg of the University of Arizona studied Europa's
surface, which appears to be only about 50 million years old - roughly 1
percent of the age of the solar system - and continually reforming.
He considered three possible 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 oxygen at the surface,
Greenberg found that the delivery rate into the ocean is likely so fast that
the oxygen concentration could exceed that of the Earth's oceans in only a few
million years.
These concentrations of oxygen could be great enough to
support not only microorganisms, but also larger animals that have greater
oxygen demands, Greenberg said.
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, or rusting. 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.
Greenberg will present his findings Friday at the 41st
meeting of the American Astronomical Society's Division for Planetary Sciences
in Fajardo, Puerto Rico.
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