You will find
What makes Europa pink?
Does Europa's rosy glow betray a flourishing colony of
THE red tinge of Europa, one of Jupiter's moons, could
be caused by frozen bits of bacteria. Their presence
would also help explain Europa's mysterious infrared
signal. Europa is mostly frozen water, but it absorbs
infrared radiation differently to how normal ice does.
Researchers think this is because something is binding
the water molecules together. Salts of magnesium
sulphate frozen within the ice, for example, would
make the molecules vibrate at different frequencies.
But no one has managed to come up with the perfect mix
of salts to explain all of Europa's spectrum.
Astrogeophysicist Brad Dalton wondered if something
else was bound up with the water molecules. "Just on a
lark, I asked a colleague of mine at Yellowstone if he
had any IR spectra of extremophile bacteria," he says,
and he was shocked by how well they matched Europa's
mysterious spectrum. Then he analysed three kinds of
bacteria under the same sort of conditions as Europa:
its temperature is about -170 íC and at 0.01 millibars
it has virtually no atmosphere.
Preliminary results show that all three species, the
ordinary gut bacteria Escherichia coli, and
extremophiles Deinococcus radiodurans and Sulfolobus
shibatae, are just as good at explaining Europa's IR
spectrum as the salts. However Dalton says the two
species that thrive under extreme conditions are
obviously more likely candidates for life on the icy
moon. They also happen to be pink and brown, which
would help explain the red patches on the moon's face.
Bacteria couldn't survive on Europa's surface, but
there might be liquid water inside Europa's icy crust
capable of supporting life. "They could be blasted out
to the surface in some kind of eruption and flash
frozen," says Dalton. He plans to present his results
at the Lunar and Planetary Science conference next
Glenn Teeter from the Pacific Northwest National
Laboratory in Washington state says bacteria aren't
the simplest explanation for Europa's spectrum. "It
does strike me as a bit far fetched," he says. But it
can't be ruled out until we go there to see.
Best, Jeff Davis
"Everything's hard till you know how to do it."
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