Science Seminars

9/15/2011 – Enceladus and its Subsurface Ocean

Speaker: Sascha Kempf, LASP
Date: Thursday, Sep 15, 2011
Time: 4pm
Location: LSTB

Seminar Abstract:

Saturn’s ice moon Enceladus turned out to be one of the most intriguing bodies in the solar system. Data returned by several instruments on the Cassini spacecraft provide compelling evidence that this moon is unusually active and is capable of maintaining a pronounced ice volcanism. In particular, measurements of the spatial distribution of the plume particles recorded by Cassini’s dust detector CDA provided the first evidence for a local source of ice grains in the moon’s south polar terrain.Data returned by the neutral gas spectrometer INMS, the UV camera UVIS, and images by the Cassini camera lead to the surprising conclusion that the plume particles are expelled more slowly than the water vapour from the moon’s interior although the grains were expected to be tightly bound to the gas flow within the vents. By assuming that the grains’ motion is strongly affected by collisions withthe vents’ walls, a model proposed by Schmidt et al. matches all plume data available so far. The most important conclusion of this model is that the temperature at the bottom of the cracks must be 260K or higher, suggesting the possibility of a subsurface water reservoir. The discovery of a ring particle population rich on sodium salts, which can arise only if the plume particles are formed from liquid water, strongly supports the existence of a large liquid water reservoir in contact with Enceladus’ rockycore. Composition data obtained during a close Enceladus flyby in 2008 revealed that 99% of the ejected solid material are sodium-rich slow particles, while Saturn’s E ring is dominantly replenished with fast sodium-poor dust grains.