WWW.ASTRONOMY.COM 29Saturn. The valiant explorer’s immolation
is pre-planned. Flight engineers will con-
trol the spacecraft so it will not accidentally
make landfall on Enceladus or Titan,
moons that present promising sites for exo-
biology. Enceladus’ icy crust, festooned
with gossamer curtains of water geysers,
hides a global ocean of brine, a potential
biome to be protected. Titan’s environment
may harbor prebiotic conditions similar to
those found on primordial Earth.
A new path
Those moons were still largely unknown
quantities before Cassini’s multiple-
encounter mission, says Cassini Imaging
Team Lead Carolyn Porco. “Titan was one
of our major mission targets. Remember
what we didn’t know, even after the
Voyager f lybys. The Voyager cameras’ spec-
tral capabilities basically cut out at exactly
the place in the electromagnetic spectrum
where you could start seeing down to the
surface of Titan. All we saw was fog.”
Now that Cassini has peered through
that veil, she says, “It’s been so enjoyable to
find things that look so Earth-like. The
dune fields that cover the whole equatorial
and mid-latitudes are remarkable. Titan is
so geographically and geologically com-
plex, very like the Earth in that respect,
and also unlike it at the same time.”
Larger than Mercury, Titan supplies
gravity that has been an important tool
throughout Cassini’s reconnaissance. “It
has been the body that provided us with
the means to tweak the Cassini trajectory
around; otherwise it would have required aprohibitive amount of fuel. All the major
changes to the orbit were done with f lybys
of Titan. Programmatically, it’s been criti-
cal,” Porco says.
Titan’s gravity also provided mission
planners with a way to direct the f light
path of the craft inward last November,
enabling Cassini to skim the rings at closer
range than at any other time in the nearly
two-decade mission.
Titan is not the first body to assist in
Cassini’s f light path. In fact, “gravitational
assists” bracket Cassini’s journey. The bus-
sized spacecraft’s arduous seven-year jour-
ney from Earth culminated July 1, 2004, as
Cassini rocketed into orbit around the lord
of the rings. That transit from Earth to
Saturn included four planetary flybys: two
with Venus (in April 1998 and June 1999),