STORMY WEATHER
Clouds of ammonia
and ice in Saturn’s
atmosphere produce
huge electrical storms
that rage for weeks
or months. Early in its
mission, Cassini started
to detect lightning on
Saturn using its radio
instruments, but recently
the probe released the
first-ever movie of
lightning on another
planet, showing a 190-
mile-long flash from a
10-month storm in 2009.
YOUTHFUL COMPANIONS
Saturn’s rings consist of water-ice particles—
typically ranging in size from a few inches to
many feet—that continually gather into clumps
and drift apart again. The particles’ incredible
brightness makes some astronomers suspect
that the rings are much younger than the planet:
If they were old, they would have been darkened
by accumulated carbon from meteoroid impacts.
In 2017 the Cassini probe will plunge between the
planet and its innermost ring, which should reveal
much about the rings’ age and composition.
Much like the ancient holiday of Saturnalia, when Roman
masters swapped roles with servants, the recent buzz surround-ing Saturn has mainly focused not on the giant planet but on its
satellites. And with good reason: The largest of those moons,
3,200-mile-wide Titan, has an atmosphere that may be similar
to that of our own planet in its younger days, and Enceladus, a
300-mile-wide ball, has a geologically active surface. Another
Saturnian satellite, two-faced Iapetus, puzzles astronomers with
one bright hemisphere and one that is as black as coal. But
recent images from the Cassini spacecraft, whose mission has
just been extended to 2017, are putting Saturn itself back in the
spotlight, giving us new information about the planet’s powerful weather patterns and the structure of its glorious rings. The
major rings are designated A, B, and C (running inward from
the outermost ring). LAURIE RICH SALERNO
INVISIBLE RING
The Cassini Division—a
dark swath between
Saturn’s broad A and B
rings—looks empty, but
it is actually a separate
ring, just one with fewer
particles. NASA’s Voyager
discovered this hidden
material, and the Cassini
probe shows previously
unseen ringlets and gaps
within it. The cause of
some of those gaps is
not evident; in January,
a group of astronomers
proposed that they result
from the gravitational pull
of particles in the giant,
nearby B ring.
