Two hundred and fifteen years ago today (August 28), Sir William Herschel discovered Saturn’s moon Enceladus (499 kilometers, 310 miles across). A mission goal for Cassini is to determine the composition of moons like Enceladus.
Along with most of the other 33 satellites, Enceladus appears to have an icy crust. Condensed ices give the moons very high albedo (reflection coefficients) but are mottled with darker regions that may be rich in organic chemicals like methane or ammonia.
These building blocks for primitive biochemistry may offer insight into how a similar, but much warmer environment on Earth, might have given rise to primordial life.
Cassini will conduct its four-year orbital mission, circling Saturn 77 times and cruising by more than 50 close encounters (and another dozen or so more-distant encounters) with the planet’s moons.
In all, Cassini will aim its instruments at 8 of Saturn’s 33 known moons. Cassini has already discovered a few that were unknown from ground observation and an earlier Voyager flyby.
Titan will get the lion’s share of attention: 45 close flybys are planned for the giant moon. Titan will also be the target of the Huygens probe, which will be released by Cassini on Christmas day (Christmas eve in the U.S.) for descent through Titan’s atmosphere 3 weeks later.
Titan is of particular interest to scientists because, like Earth, it has an atmosphere that contains nitrogen and organic molecules such as methane. Some scientists speculate that Titan’s chemistry may offer a snapshot of what Earth’s chemistry was like before life took hold.
After Cassini releases the Huygens probe, it will spend about 10 exploring several of Saturn’s icy satellites. Cassini will make close flybys of Enceladus, Hyperion, Dione and Rhea during this grand lunar tour.
