Saturn moon caught stealing particles from one of the planet's
rings
Stealing is a crime on Earth, but on Saturn, apparently it is
routine. The Cassini spacecraft has witnessed Saturn's moon
Prometheus snatching particles from one of Saturn's rings.
This potato-shaped moon is also believed to be responsible for
kinks within Saturn's thin F ring, a contorted, narrow ring flanked
by two small moons, Prometheus and Pandora. The thievery and
the detailed behavior of kinks were observed for the first time
ever in images taken by the Cassini spacecraft.
In an image taken on October 29, Prometheus is seen stealing
particles from the F ring while connected to the ringlets by a
faint streak of material. A movie sequence of the ring, taken on
October 28, captures in freeze-frame motion the zigzagging kinks
and knots, some of which are almost certainly caused by
Prometheus.
The kinks look like "hiccups" traveling around the ring.
Consisting of 44 frames taken three minutes apart, the sequence
represents almost two hours, or about one-eighth of the orbital
period of F ring particles around the planet.
Cassini was on a flight path that took the spacecraft away from
the planet and farther south, so that the rings appear to tilt
upward. The top portion of the F ring is closer to the spacecraft,
while the bottom portion is farther away and curves around the far
side of Saturn.
Scientists are not sure exactly how Prometheus is interacting
with the F ring here, but they have speculated that the moon might
be gravitationally pulling material away from the ring. Scientists
speculate that the ring particles may end up in a slightly
different orbit from the one they were in prior to getting a "kick"
from the moon. These kicks occur at specific locations in the rings
and can actually cause large waves or knots to form. In
the still image, gaps in the diffuse inner strands are seen. All
these features appear to be due to the influence of Prometheus in
ways that are not fully understood.
Saturn's moon Prometheus is following in the footsteps of the
legendary Titan for which it is named. In Greek mythology,
Prometheus stole fire from the gods and gave it to the mortals.
Scientists will use what they learn about Prometheus' interaction
with the F ring to understand the gravitational exchanges between
moons and rings, which give rise to so much of the structure that
is observed in Saturn's rings.