NASA’s Cassini spacecraft has found two new, partial rings around Saturn that each accompany a small moon, shedding light on what determines whether a partial or complete ring forms with the moon.
The partial rings, called ring arcs, extend ahead of and behind the small Saturnian moons Anthe and Methone in their orbits.
Both Anthe and Methone orbit Saturn in locations called resonances, where the gravity of the nearby larger moon Mimas disturbs their orbits. Mimas provides a regular gravitational tug on each moon, which causes the moons to skip forward and backward within an arc-shaped region along their orbital paths, said Nick Cooper of Queen Mary, University of London an a member of the Cassini imaging team.
Scientists believe that the faint ring arcs likely consist of material knocked off the small moons by micrometeoroid impacts. The material doesn’t spread all the way around Saturn to form a complete ring because the interactions of the moons with Mimas confine the material to a narrow region along the moons’ orbits.