Introduction
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 as well as an initial two-year extended mission called the Cassini Equinox Mission, the spacecraft is conducting a second extended mission called the Cassini Solstice 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, Cassini 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. The moon’s diameter is about 500 kilometers (around 300 miles) 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 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 first, two-year Cassini Equinox Mission brought continued excitement. During that extended mission the spacecraft made 60 additional orbits of Saturn, 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 also took place.
Why the "Cassini Solstice Mission?"
Cassini arrived just after Saturn's northern winter solstice, and this latest extension continues until a few months past northern summer solstice in May 2017. The northern summer solstice marks the beginning of summer in the northern hemisphere and winter in the southern hemisphere.
A complete seasonal period on Saturn has never been studied at this level of detail. The Solstice mission schedule calls for an additional 155 orbits around the planet, 54 flybys of Titan and 11 flybys of the icy moon Enceladus.
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. The situation is similar at Saturn. With a healthy spacecraft and a powerful suite of instruments, Cassini scientists will continue to monitor the changing seasons on Titan and Saturn.
Science Objectives
The Cassini Solstice 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 Scientists hope to learn answers to many questions that have developed during the course of the mission, including why Saturn seems to have an inconsistent rotation rate and how a probable subsurface ocean feeds the Enceladus' jets.
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.
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