Feature | August 21, 2017

Nine Ways Cassini Matters: No. 5


Saturn's moon Iapetus. Saturn and Jupiter are unrivaled in our solar system for the sheer number of moons captured in their orbits.

Cassini revealed Saturn’s moons to be unique worlds with their own stories to tell.

Planet-size Titan and diminutive Enceladus stood out in Cassini’s in-depth survey of Saturn’s moons. But the mission showed that every moon in the Saturn system is a unique character with its own mysteries, and many of Saturn’s satellites are related in surprising ways.

This false-color view of Saturn's moon Hyperion reveals crisp details across the strange, tumbling moon's surface.

For example, Cassini data enabled scientists to confirm earlier suspicions that Phoebe is likely an object from the outer solar system beyond Neptune, captured by Saturn’s gravity long ago. Phoebe also turns out to be key to the two-toned appearance of the moon Iapetus: As Phoebe sheds its dark dust, it coats the leading side of Iapetus and causes ice to heat up and migrate to the moon’s opposite side.

Cassini also gave scientists a better understanding of why Hyperion looks like a giant sponge or wasp’s nest tumbling through space. Researchers determined that the moon’s density is so low that impacts tend to compress its surface rather than blasting it out, and the material that is launched into space tends to escape for good, thanks to Hyperion’s low gravity.

Cassini found that Enceladus is not only active, but that its geologic activity is creating Saturn’s E ring and spray-painting the surfaces of several of the other moons with its highly reflective ice particles.

The mission also followed up on a mystery from the early 1980s when NASA’s Voyager spacecraft flew by the Saturn system and saw bright wispy terrains on Dione. Cassini found that the features were in fact a vast network of canyons. Cassini also detected hints of a faint atmosphere that might have been outgassed from the moon’s interior.

And Cassini watched closely over many years how Prometheus interacts with Saturn’s F ring to create features like “streamers,” “plumes” and “drapes.”