How are the rings of planets formed and what are they made out of?
Asked by: Claas Behrens
The rings around planets like Jupiter and Saturn
(yes Jupiter has rings!) are made up of bits of
ice and rock.
They form when asteroids,comets, or any other
large objects pass too close to the planet and are
torn apart by the planet's gravity. There is a
point around the planets called the Roche Limit.
This is the point where gravity will tear apart
an incoming object, and prevent the particles
from re-accreting back into a larger object.
Essentially, rings are just thousands of tiny
moonlets that orbit a planet and don't clump back
into larger objects.
Answered by: Mike Perkins, Physics/Astronomy Major, Penn State
A planet is believed to form when the mutual gravitational attraction of debris orbiting a
star accumulates into a growing mass. Some of the coalescing material orbiting a
protoplanet can do the same thing, forming the planet's satellites, or 'moons'. (Some
smaller satellites, though, are believed to be just 'captured', already formed, asteroids.)
There is a problem, however, if the debris orbiting a planet orbits too closely. Because
gravitational force varies with distance, the different accelerations between two points
at different distances from a massive object create a tidal force that has a stretching
effect on nearby objects. This force from the Sun and Moon creates tides on opposite
sides of the Earth, for example. When the tidal force is large enough, it overcomes the
gravitational forces trying to bring individual particles together. Within a given distance
from a planet, called its 'Roche Limit', tidal forces prevent debris from aggregating into
Planetary rings, then, consist of millions of separate small rock and ice particles, each
maintaining their own orbit around the host planet. From a distance, these small orbiting
particles only APPEAR to be a continuous, solid ring.
Answered by: Paul Walorski, B.A., Part-time Physics Instructor
'I never worry about the future. It comes soon enough.'