“Enceladus is almost
certainly habitable –
we just don’t know
whether it’s inhabited”
David Rothery, The Open UniversityJonathan Lunine, a planetary scientist at
Cornell University. Spurred on by the
discovery of Enceladus’ water plumes, the
spacecraft operators designed a sequence of
f lybys that would take Cassini deeper and
deeper into the plumes.
“We now have an inventory of organic
molecules,” says Lunine. “It is not a
complete list but it is enough to be able to
say, yes we have carbon-bearing molecules
inside Enceladus.” This could be a
significant discovery, because on Earth,
life-giving DNA is built using carbon-
bearing molecules.
On 28 October 2015, Cassini plunged to
its closest f lyby yet, just 48km above the icy
surface and hopefully steering through the
densest part of the geysers. Planetary
scientists are now eagerly analysing the
results. They are on the look out for
molecules of hydrogen, because if this gas is
present in the water jets, theory suggests that
it must becoming from where hot water is
reacting with rocks on the ocean f loor.Finding the molecule has implications
for life. “Hydrogen can feed an organic
pathway. A microbe could bond hydrogen
onto carbon and get an energy kick out of
it,” says Rothery. This is how microbes
called methanogens survive on Earth.
Of course, finding the chemicalingredients for such life does not guarantee
that it is there. Nevertheless, this wealth of
new information is edging Enceladus ahead
of Europa in terms of where planetary
scientists think that life might be found.
“I’m inclined to boost Enceladus higher
than Europa now,” says Rothery, “It’s
almost certainly habitable – we just don’t
know whether it’s inhabited.”
For now, there are no further plans to
send anything back to the Saturn-
Enceladus system. Once the Cassini
mission ends, however, and planetary
scientists start to really digest the new
information, the chances are that a follow-
on astrobiology-oriented mission
will begin to gather support.