NASA’s Cassini spacecraft successfully completed its second-closest encounter with Saturn’s icy moon Helene on June 18, 2011, beaming down raw images of the small moon.
At closest approach, Cassini flew within 4,330 miles (6,968 kilometers) of Helene’s surface. It was the second closest approach to Helene of the entire mission.
Appropriately named, Helene is one of four known Trojan moons, so called because it orbits at a Lagrange point.
A Lagrange point is a gravitationally stable position near two massive bodies, in this case Saturn and larger moon Dione. In fact, irregularly shaped ( about 36 by 32 by 30 kilometers) Helene orbits at Dione’s leading Lagrange point while brotherly ice moon Polydeuces follows at Dione’s trailing Lagrange point. The sharp stereo anaglyph was constructed from two Cassini images (N00172886, N00172892) captured during the recent close flyby. It shows part of the Saturn-facing hemisphere of Helene mottled with craters and gully-like features.
Image credit: NASA/JPL-Caltech/Space Science Institute