Astronomy Picture of the Day

A Wave Maker Moon in Saturn's Rings

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A Wave Maker Moon in Saturn's Rings

What causes small waves in Saturn's rings?

Observations of rings bordering the
Keeler gap in
Saturn's rings showed unusual waves.

Such waves were first noticed last July and are
shown above in clear detail.

The picture is a digitally foreshortened
image mosaic taken earlier this month by the
robot Cassini spacecraft now orbiting

The rings, made of many
small particles, were somehow not orbiting Saturn in their usual manner.

Close inspection of the
image shows the reason - a small moon is orbiting in the Keeler gap.

The previously unknown moon is estimated
to span about seven kilometers and appears to have the same
brightness as nearby ring particles.

The gravity of the small moon likely perturbs the orbits of
ring particles that come near it,
causing them to shimmy back and forth after the moon passes.

Since inner particles orbit more quickly than outer particles,
only the leading particles of the inner rings and the
trailing particles of the outer rings show the wave effect.

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