The orbiter and lander arrived in July 2004 like wide-eyed tourists at Saturn, the realm of mystery and rings. Shortly thereafter, in December 2004, Huygens departed the mother ship and made the first landing on an alien moon, touching down in the hydrocarbon slushes of Titan three weeks later.
Cassini was just settling in for a long stay, circling Saturn like a pesky interplanetary paparazzo.
A list of its greatest hits would include movies of the six-sided storm that hugs the planet’s north pole; detailed views of Saturn’s spidery golden rings, woven into warps, braids and knots by the gravity of tiny moonlets; the discovery of plumes that look like snow-making machines shooting from the surface of the moon Enceladus. Not to mention postcards of lakes and seas on Titan.
NASA, not shy about sharing its accomplishments, recently released a blizzard of numbers summarizing the mission: 4.9 billion miles traveled, 294 orbits of Saturn completed, 2.5 million commands executed, 635 gigabytes of science data collected, 453,048 images taken, 3,948 science papers published, 27 nations participating and two oceans discovered.
To which must be added: $2.5 billion to build and launch Cassini and Huygens, split between NASA, E.S.A. and the Italian Space Agency, and another $1.4 billion to run them for 20 years in flight.
Like great scientific endeavors, Cassini raised as many questions as it answered. What, for example, is going on in those oceans on Titan and Enceladus?
Titan, the only moon in the solar system to have a thick atmosphere — even thicker than the Earth’s — is now the only body in the universe known to have liquid on its surface. That liquid is not water, but methane and ethane — hydrocarbons. The air on Titan is almost pure nitrogen. In addition, there may be an ocean of water or some other liquid substance deep under the surface.
If you think that Life As We Don’t Quite Know It could be based on some liquid other than water — a possibility suggested by Steven Benner, a biochemist at the Foundation for Applied Molecular Evolution in Florida — Titan has the potential to be Exhibit Number One. In recent years, proposals have been floated to send balloons, boats and even a submarine to Titan to check out whatever chemistry might be going on in its frigid wastes.