Nearly eight months after Cassini entered into orbit around Saturn, the spacecraft has amassed quite a collection of images of the ringed planet and its moons. A suite of articles published in the current Science discusses observations made thus far in the mission. Highlights from this grand tour follow below.
A close flyby of Phoebe, Saturn's outermost moon, revealed an ancient, pockmarked surface. The many craters are thought to have resulted from collisions with smaller objects. Twenty-four of the largest ones have been deemed conspicuous enough to receive names from the International Astronomical Union. Images obtained using the Cassini Imaging Science Subsystem (ISS) also suggest that the tiny moon contains ice at shallow depths-perhaps just 300 to 500 meters below the darker surface material.
Saturn's rings have inspired wonder ever since Galileo first glimpsed them in 1610. Thanks to new observations, they are more alluring than ever. Images produced by the ISS have revealed new moons within the rings. They also indicate that diffuse rings populate gaps within the main rings. Up close and personal, the pictures even document the particle properties of the planet's lovely ornaments.
It might look serene from Earth, but Saturn is a tempestuous place. Astronomers have long known that winds in the ringed planet's equatorial region rage at speeds approaching 10 times that of Earth's jet stream. The new findings show that these gusts change with altitude, with wind speeds decreasing with height. Energy transferred by convection from Saturn's interior appears to be fueling the cloud-level winds. Cassini has also pinpointed the source of powerful electrostatic discharges first documented by the Voyager spacecraft flybys more than 24 years ago. Scientists attributed the earlier lightning observations to unseen storm activity in the planet's equatorial region. Fresh evidence reveals that they are indeed one and the same. Why Saturn's lightning is so much more intense than Earth's remains a mystery, however.