WWW.ASTRONOMY.COM 53refilled a number of times over the
course of Titan’s history. That story is
told in the layers of sediment, not only
on the coastline, but also on the seaf loor.
It may be prudent to do some surface
exploration of the seas with a boat first,
something akin to the HMS Challenger
expedition of 1872 to 1876. As part of the
world’s first global oceanographic expe-
dition, the Challenger crew sampled the
seaf loor by lowering a simple weight
with a hole in the bottom before winch-
ing it back up. A Titan boat could
explore the depths in similar fashion.
But are these underwater explorers our
best option for exploring the seas of
other worlds like Titan?
“If you’re asking me, ‘Is a submarine
cool?’, the answer’s definitely yes,”
Lorenz says. “Are the seas worth explor-
ing? Definitely, yes. Is a submarine
the next logical step in Titan explora-
tion? I’m not so sure. It’s a whole new
world, and there are an awful lot of
unknowns. Maybe a sub is a step or two
away.”
Titan is a wonderfully alien world, but
when it comes to the search for life, the
majority of astrobiologists have their eyesset on other targets. Stone puts it this
way: “The possibility of life on Europa
and Enceladus is pretty good; it’s non-
zero. Life acts like a battery. It needs elec-
tron donors, it needs electron receptors,
it needs water, and it needs carbon.
Those four constituents are likely to exist
on Europa and Enceladus. Both are good
targets. There are other ocean worlds out
there, but by far and away, Europa is the
one to cut our teeth on.”
Stone points out that a Europa f lyby
mission — NASA’s Europa Clipper — is
fully in motion and set for launch some-
time between 2022 and 2025. Further-
more, a proposed lightweight companion
craft, named the Europa Lander, is cur-
rently accepting instrument proposals.
So, although researchers would love to
explore the seas of Titan, Europa will
likely be the first world to have its water
appraised. Either way, the pieces seem to
be falling into place for a voyage to the
bottom of an alien sea.“The possibility of life on Europa and
Enceladus is pretty good; it’s non-zero.
Life acts like a battery.”
A robotic
submarine explores
the depths of
Kraken Mare, the
largest body of
water on Saturn’s
largest moon,
Titan. Using radar,
such a sub could
map the seafloor
of Titan, perhaps
uncovering
life-supporting
hydrothermal vents
like those found
at the bottom of
Earth’s oceans.
NASA GLENN RESEARCH CENTERFrequent Astronomy contributor Michael
Carroll featured planetary submarines in his
latest scientific novel, Europa’s Lost Expedition
(Springer, 2017).