An artist’s concept of the Cassini spacecraft flyby of Enceladus, Saturn’s small, geologically active moon

Credit: NASA/JPL

NASA's Saturn-orbiting Cassini spacecraft will be flying very close to Saturn's moon Enceladus, for a gravity experiment, designed to study the internal composition of Enceladus (504 km across). During its Enceladus flyby, scheduled on 28 April, intrepid Cassini will venture through the water-rich plume erupting from Enceladus's south polar region. At closest approach, Cassini will be about 100 km from Enceladus.

Scientists plan to apply a radio instrument aboard Cassini to measure the gravitational pull of Enceladus. By detecting the radio signals from Cassini, during the maneuver, scientists may probe the interior structure of Enceladus, and identify the nature of the source of the plume.

A Close-up image from the Cassini spacecraft, showing the plume of Enceladus
Credit: NASA/JPL/Space Science Institute

The cold plume, which consists of water vapor and organic particles, emanates from fractures, known as the tiger stripes, as they resemble the characteristic stripes of tigers. This type of volcanic activity is termed cryovolcanism, because the erupting material is cold. Cassini discovered the cryovolcanism on Enceladus in 2005. Scientists speculate that there could be an ocean of water, or a large salt lake, beneath the surface of Enceladus.

Enceladus is a small icy moon. It orbits Saturn every 1.37 days, or 32.9 hours, at an average distance of approximately 240,000 km. Like our Moon (3,476 km across), Enceladus keeps the same side turned to its parent planet. In Greek mythology, Enceladus was one of the Giants and a brother of Cronus (Saturn), the leader of the Titans. 
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency (ESA) and the Italian Space Agency (ASI). The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology (Caltech), manages the Cassini-Huygens mission for NASA.

Further Reading
The Cassini Mission Websites
http://www.nasa.gov/cassini
http://saturn.jpl.nasa.gov 

Aymen Mohamed Ibrahem
Senior Astronomy Specialist