The mysterious world of Enceladus
NASA’s Cassini spacecraft has been exploring the mini solar system
surrounding the planet Saturn since its arrival in July 2004. The
Saturn system includes the familiar bright rings, a multitude of moons,
and Saturn’s magnetosphere, the vastly larger but invisible region of
space that is controlled by Saturn’s magnetic field.
The magnetosphere is populated and dynamically driven by hot plasma
(ionized gas) deriving from the satellites and ring particles that
reside within it. One of those satellites, Enceladus, appears to be
geologically active, and hence a dominant source not only of solid ring
material but also of magnetospheric plasma.
The first figure (courtesy of the Cassini imaging science team)
shows a color-coded image of icy dust particles emanating from the
south pole region of Enceladus, already recognized as a “geothermal hot
spot” based on other Cassini measurements during its close encounter
with Enceladus in July 2005. During that same encounter, the Cassini
Plasma Spectrometer (CAPS) found dramatic deviations from the otherwise
smooth rotational flow of magnetospheric plasma in a surrounding region
about 30 times larger than Enceladus.
The second figure shows the observed plasma velocities (in red)
compared to a theoretical model of the plasma flow (in blue) developed
recently at Rice. The data-model comparison suggests that Enceladus
expels nearly a ton/second of water vapor into the surrounding space,
exceeding previous estimates, and making Enceladus the engine that
powers the much larger magnetosphere of Saturn.
This work is reported in a paper by Duane Pontius and Tom Hill
submitted to the Journal of Geophysical Research. Pontius (Rice Ph.D.,
1987) is a professor at Birmingham Southern College who spent his Fall
2005 sabbatical at Rice collaborating with Hill (Rice Ph.D., 1973), now
a professor in the Rice Physics and Astronomy Department and a
co-investigator for the CAPS experiment. The principal investigator for
CAPS is David Young (Rice Ph.D., 1970) of the Southwest Research
Institute in San Antonio.