NASA
scientists think they might have a lead on where to find Saturn's missing moons: near rings
recently discovered by the Cassini spacecraft.
In
mid-September, the sun was poised behind Saturn, providing Cassini
scientists with an unprecedented imaging opportunity.
Under the
cover of the planet's shadow, the entire ring system became visible, and
never-before-seen microscopic particles began to appear.
The
spacecraft discovered a single, faint new ring at the orbits of two moonlets, Janus and Epimetheus. A second,
narrow ring that overlies the orbit of the tiny moon Pallene
was found a week later. A third and fourth ring are visible in the Cassini Division, the big gap in Saturn's main ring system.
Scientists
suspect a moon might be lurking near one of the new rings.
"Just like
the old maxim that says where there's smoke, there's fire, at Saturn, where
there's a new ring, there's bound to be a moon," said Jeff Cuzzi,
a Cassini scientist at NASA's Ames Research
Center.
Saturn's
smallest moons have weak gravity and cannot retain any loose material on their
surfaces. When these moons are struck by rapidly moving interplanetary
meteoroids, this loose material is blasted off their surfaces and into Saturn
orbit, creating diffuse rings along the moon's orbital path.
Collisions
among several moonlets, or boulder-sized rubble, might also lead to debris
trails. For instance, Saturn's G ring doesn't seem to have any single moon
large enough to see ─ it might have formed from a recent breakup of a
moon.
"We are hot
on the trail of these possible elusive moonlets," said Joe Burn, Cassini imaging scientist at Cornell University.
"Finding the moons and learning about their interactions with the rings will
help us understand how the moons formed and perhaps how the Saturn system
formed."
The Cassini spacecraft was also able to take advantage of the
unusual viewing alignment to note distinct color differences in the rings.
These differences could indicate variations in compositions and in
microscopic particles in the rings. They could also imply the particles are
being sorted by size.
"The main
rings show a neutral color, while the C ring is reddish, and the D and E rings
are quite blue," said Phil Nicholson, another Cassini
scientist at Cornell. "We don't quite understand if these variations are due to
differences in particle size or composition, but it's nice to be surprised
every once in awhile."
advertisement
