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 °C and at 0.01 millibars it has virtually no
atmosphere.
Advertisement
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 spring.
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.