Jet Propulsion Laboratory

On June 30, 2004, the Cassini spacecraft entered orbit around Saturn to begin the first in-depth, up-close study of the ringed planet and its domain. As expected, the Saturn System has provided an incredible wealth of opportunities for exploration and discovery. With its initial four-year tour of the Saturn system complete, the spacecraft is conducting an extended mission called the Cassini Equinox Mission.

"We're looking at a string of remarkable discoveries -- about Saturn's magnificent rings, its amazing moons, its dynamic magnetosphere and about Titan's surface and atmosphere," says Dr. Linda Spilker, deputy project scientist. "Some of the mission highlights so far include discovering that Titan has Earth-like processes and that the small moon Enceladus has a hot-spot at its southern pole, jets on the surface that spew out ice crystals and evidence of liquid water beneath its surface."

Cassini's observations of Saturn's largest moon, Titan, have given scientists a glimpse of what Earth might have been like before life evolved. They now believe Titan possesses many parallels to Earth, including lakes, rivers, channels, dunes, rain, snow, clouds, mountains and possibly volcanoes.

The spray of icy particles from the surface jets collectively forms a towering plume three times taller than the width of Enceladus. It is now thought that the plume feeds particles into Saturn's most expansive ring, the E ring. Already in the extended mission, the spacecraft has come as close as 25 kilometers (15 miles) from the moon's surface.

The extraordinary results from the Cassini spacecraft and the European Space Agency's Huygens probe, which plunged through Titan's dense, smoggy atmosphere to its surface, have generated hundreds of scientific articles and been the subject of special issues of the world’s most important scientific journals.

The first four years of the Cassini-Huygens saga brought a new dimension of understanding of the complex and diverse Saturn system. The two year Cassini Equinox Mission is expected to be just as exciting. During the extended mission the spacecraft will make 60 additional orbits of Saturn, including 26 flybys of Titan, seven of Enceladus, and one each of Dione, Rhea and Helene. Investigations of Saturn's rings, the planet itself and new places within Saturn's magnetosphere await.

Why the "Cassini Equinox Mission?"

Just as on Earth, equinox is a time of change in the Saturn system. An alien spacecraft dispatched to Earth could gain much greater insight into our planet’s workings by observing seasonal changes in the atmosphere, oceans and land, and the situation is similar at Saturn. With a healthy spacecraft and a powerful suite of instruments, Cassini scientists will monitor the changing seasons on Titan and Saturn and observe unique ring events, like shadows cast by rippling waves in the rings, during the 2009 equinox passage of the sun through the plane of the rings.

Science Objectives

The Cassini Equinox Mission is guided by a basic set of science goals that address major scientific questions about the planet, its magnetosphere and rings, Titan and the other icy moons. These objectives are listed in each of the following sections devoted to those topics. Some of the objectives relate to monitoring for seasonal changes in the Saturn System; others are related to new questions spawned by Cassini’s investigations during its first four years at Saturn.

A separate team of scientists plans the observation and measurements for each of the spacecraft's 12 instruments and then analyzes the returned data. Each team is headed by a team leader or a principal investigator. Hundreds scientists from the US, Europe, and across the globe participate in this international mission of exploration and discovery. See Cassini Orbiter Instruments for more.