One of the major missions that MSSL is involved in is Cassini-Huygens: a NASA/ESA/ASI mission to Saturn and its moons. After almost 4 years looping arund the planet and gathering a immensely valuable set of data, it’s been announced that the mission will be extended to 2010. Some of the mission’s highlights so far include the landing of the European Huygens probe on the surface of Titan, Saturn’s largest moon, the discovery of geysers of water vapour and ice grains emanating from the moon Enceladus’s south pole, an atmosphere surrounding Saturn’s rings, and the possible detection of a disk of debris or rings around the second-largest moon, Rhea.
MSSL’s contribution is the Cassini Plasma Spectrometer’s Electron Spectrometer, or CAPS-ELS. This instrument senses the electrons in Cassini’s vicinity, helping build up our understanding of Saturn’s magnetosphere – a huge bubble of charged gas that surrounds the planet, and how it interacts with the planet’s moons and rings.
Titan’s upper atmosphere from Cassini (NASA/JPL/SSI)
ELS is also telling us some very unexpected things: a major surprise of the mission has been at Titan. During several flybys of this moon, ELS has recorded very strange signatures. The only particles that fit these signatures aren’t electrons at all, but negative ions. The vast majority of atoms and molecules in Titan’s upper atmosphere have a positive electrical charge, but ELS has shown that there are lots of negative ions there too, providing a key piece of information for understanding the complex chemistry that goes on there.
Cassini’s mission extension, beginning on July 1, will include 21 Titan flybys, 7 Enceladus flybys, and several flybys of other moons including Mimas, Tethys, Dione, Rhea, and tiny Helene. The Planetary Society have compiled a handy list of key events during the prime and extended missions.
Some of the biggest results to come from Cassini so far include many unexpected discoveries, coming from instruments that weren’t designed to observe what they’ve found: as well as ELS’s discovery of negative ions, Enceladus’s south polar plume was first sensed by the magnetometer, and Rhea’s suspected ring system wasn’t found by a camera, but by the suite of magnetospheric instruments. The chances are high that there will be more surprises in store over the coming two years…
