Cassini completed its initial four-year mission to explore the Saturn System in June 2008 and the first extended mission, called the Cassini Equinox Mission, in September 2010. Now, the healthy spacecraft is seeking to make exciting new discoveries in a second extended mission called the Cassini Solstice Mission.
The mission’s extension, which goes through September 2017, is named for the Saturnian summer solstice occurring in May 2017. The northern summer solstice marks the beginning of summer in the northern hemisphere and winter in the southern hemisphere. Since Cassini arrived at Saturn just after the planet's northern winter solstice, the extension will allow for the first study of a complete seasonal period.
Cassini launched in October 1997 with the European Space Agency's Huygens probe. The probe was equipped with six instruments to study Titan, Saturn's largest moon. It landed on Titan's surface on Jan. 14, 2005, and returned spectacular results.
Meanwhile, Cassini's 12 instruments have returned a daily stream of data from Saturn's system since arriving at Saturn in 2004.
Among the most important targets of the mission are the moons Titan and Enceladus, as well as some of Saturn’s other icy moons. Towards the end of the mission, Cassini will make closer studies of the planet and its rings.
Small, icy Enceladus is of great scientific interest because it is surprisingly active. Cassini discovered an icy plume shooting from this moon, and subsequent observations have revealed the spray contains complex organic chemicals. Tidal heating is keeping Enceladus warm, and hotspots associated with the fountains have been pinpointed. With heat, organic chemicals and, potentially liquid water, Enceladus could be a place where primitive life forms might evolve. Questions surrounding Enceladus’s “astrobiological potential” are at the heart of many investigations being conducted in the Solstice Mission.
Cassini catapulted our knowledge of giant, haze-enshrouded Titan into a whole new realm. During the primary and extended missions Cassini investigated the structure and complex organic chemistry of Titan's thick, smog-filled atmosphere. On the frigid, alien surface, the spacecraft and its Huygens probe revealed vast methane lakes and widespread stretches of wind-sculpted hydrocarbon sand dunes. Cassini researchers also deduced the presence of an internal, liquid water-ammonia ocean.
Titan remains a top priority as scientists hope to catch the moon’s surface features in the act of changing. The spacecraft will look for signs of seasonal climate change such as storms, flooding, or changes in lake levels, as well as evidence of volcanic activity.
The spacecraft eventually will make repeated dives between Saturn and its rings to obtain in depth knowledge of the gas giant. During these close encounters, the spacecraft will study the internal structure of Saturn, its magnetic fluctuations, and the mass of the rings.
From a distance the rings look ordered and tidy. But up close, Cassini finds Saturn’s rings to be a complex place where small moons and ring particles jostle and collide, where waves and jets constantly form and dissipate.
Cassini is revisiting many of Saturn’s icy moons in the Solstice Mission. Over multiple flybys, Cassini will study the intriguing bright and dark surfaces of Dione and Rhea to compare their geological and cratering histories with those of other icy moons. Scientists will also study further the unique thermal features recently discovered on Mimas.
Cassini’s continued journey carries it throughout the huge sphere of magnetic activity that surrounds Saturn. One major discovery was that water ice jets from Enceladus play a major role in Saturn’s magnetosphere. Water from the jets loads up the magnetosphere, influencing radio and auroral activity, and even causes changes in the rotation of the magnetic field itself. The Solstice mission will study these phenomena in unexplored areas of the magnetosphere and probe for links to Enceladus in addition to connections with other moons.