Cassini Mission Overview

Cassini completed its initial four-year mission to explore the Saturn System in June 2008. Now, the healthy spacecraft is working overtime on the Cassini Equinox Mission, seeking answer to new questions raised in Cassini’s first years at Saturn.

The mission’s extension, through September 2010, is named for the Saturnian equinox, which occurs in August 2009 when the sun will shine directly on the equator and then begin to illuminate the northern hemisphere and the rings’ northern face. Cassini will observe seasonal changes brought by the changing sun angle on Saturn, the rings and moons, which were illuminated from the south during the mission’s first four years.

Many repeat visits are planned for Cassini at the moons Titan and Enceladus – both important targets of the Equinox Mission.

Enceladus

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 it 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 lifeforms might evolve. Questions surrounding Enceladus’ “astrobiological potential” are at the heart of many investigations being conducted in the Equinox Mission.

Titan

Cassini catapulted our knowledge of giant, haze-enshrouded Titan into a whole new realm. During the primary mission 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-driven 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 in the act of changing. The spacecraft will look for signs of seasonal climate changes such as storms, flooding, or changes in lake levels, as well as evidence of volcanic activity.

Saturn

The shifting of sunlight from south to north on Saturn is already causing visible changes in the atmosphere. The seasonal variations in temperature, winds, and cloud patterns are expected to bring additional changes to the atmosphere in the Equinox phase of Cassini’s mission.

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. During the Equinox Mission, the changing sun angle on the rings presents a prime opportunity to look for more activity, structure and small moons within this ever-changing formation of ice and dust around Saturn.

Icy Moons

Cassini is revisiting many of Saturn’s icy moons in the Equiniox Mission. Iapetus shows signs of having frozen into an odd shape fairly early in its history. Why does it have a monumental, mountainous bulge around its equator? One side is black and one side is white: Is Iapetus itself somehow creating its two-toned face or is some other process responsible, such as material from other moons?

Cassini found what appear to be rings around the moon Rhea. Dione and Tethys showed signs of possible activity. The Equinox Mission includes return visits to each.

Magnetic Environment

Cassini’s continued journey carries it throughout the huge sphere of magnetic activity that surrounds Saturn. A major discovery has been 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 causing changes in the rotation of the magnetic field itself. The Equinox mission will study these phenomena in unexplored areas of the magnetosphere and probe the links to Enceladus in addition to connections with other moons.