Skylog: Brilliant Illuminations

Cassini Returning Enceladus Gravity Data

A steady radio link to NASA's Deep Space Network on Earth enabled Cassini's scientists to use the radio science instrument to measure the variations in the gravitational pull of Enceladus. Analyzing the wiggles will help scientists understand whether an ocean, pond or great lake lies under the famous "tiger stripe" fractures that spew water vapor and organic particles from the south polar region.

This flyby featured a high-priority RSS gravity experiment to look for mass anomalies associated with the Enceladus plume. The flyby segment began with an RSS observation of a Saturn-solar occultation, both ingress and egress, which was followed by gravity observations that continued as Cassini traveled under the south pole through the plume. These back-to-back observations required almost 30 hours of continuous Deep Space Network support provided sequentially by all three complexes. These observations will be used to look for anomalies indicating the presence or absence of mass concentrations at the south polar region of Enceladus, which may in turn provide insight into the source material for the plume.

The gravity measurement was a key test for two different hypotheses about the interior of Enceladus. One theory is that a global ocean exists beneath a thin ice crust. Another argues that there's a diapir - upward intrusion of a rock mass into overlying rock - underneath the active south polar terrain that is the source of the moon's plume. After passing Enceladus, RSS continued to monitor the spacecraft trajectory as a baseline for comparison with the flyby results.

The Magnetosphere and Plasma Science (MAPS) instruments collected data as the spacecraft passed through the plume, the Magnetospheric Imaging Instrument and the other fields and particles instruments investigated the electron environment around Enceladus, and sought to measure local gradients in the magnetic and electric fields, and in electron beams moving towards Enceladus. The Radio and Plasma Wave Science (RPWS)  instrument searched for evidence of local ionization in the plumes, and measured plasma waves and other interactions of Enceladus with its magnetic environment. RPWS also determined the amount and size of dust particles from vents contributing to the plume.