Oceans of the Solar System - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 237

those of science—for instance to act as escort to Sweden's Queen
Christina on her visit to Rome when she wanted to convert to Catholi-
cism. A brief romance seemingly flowered between the two on the
journey, to add to the storybook brio of Cassini's life. Invited to France
to advise on Paris's new observatory, he immediately became a favour-
ite of Louis XIV, the Sun King, and stayed there. Unperturbed (and
unmoved by further grumbles from Cassini's Italian colleagues), the
Pope carried on paying his Bologna salary. In his life, Cassini unrav-
elled the structure of snowflakes, found that the speed of light was
finite, discovered a gap in Saturn's rings (and as we have seen, discov-
ered Mars's icecaps), and measured the size of France, ingeniously
exploiting Galileo's discovery of Jupiter's moons as a measure. The
last of these did not overly please the Sun King, as France turned out
to be about a fifth narrower than previously thought. Poor recom-
pense, he said, for treating his astronomers so well.
On Christmas Day 2004, the spacecraft Cassini released the Euro-
pean Space Agency's Huygens space probe 146 on its journey to the
surface of Titan, the largest of Saturn's moons. Huygens entered
the atmosphere of Titan on 14 January 2005. The saucer-shaped probe
gently descended with the help of a parachute through a dense Titan
atmosphere composed of nitrogen, methane, and small amounts of
argon—this atmosphere is so cold that it contains no water vapour.
Indeed, Titan's atmosphere is locked in a primitive state, with a
composition perhaps similar to that of the early Earth. On Earth,
though, where water vapour is active, carbon compounds in the
atmosphere are rapidly oxidized to carbon dioxide. Not so on Titan.
At mid-altitude in Titan's atmosphere (above 200 kilometres from
the surface of the moon) Huygens encountered a thick smog where
photochemical reactions produce an organic rain of methane together
with nitrogen-containing aerosols. These fall steadily on to the sur-
face of the moon, creating a strange landscape of rivers and lakes,