Ever since
the Cassini spacecraft began taking pictures of Saturn and its moons last
February, scientists have had plenty of work on their plates.
Last week several new images and data from the mission were published
in the journal Science.
Among
the findings is the detection of molecular oxygen around Saturn's A ring.
( The ring system
begins from the inside out in this order: D, C, B, A, F, G, E.)
Molecular
oxygen forms when two oxygen atoms bond together. It is rarely seen beyond
Earth, where it is created continuously as a byproduct of photosynthesis in
plants.
On Saturn,
where there is no plant life, molecular oxygen must be formed in a different
way -- through a chemical reaction between the Sun's radiation and the icy
particles that comprise Saturn's rings, scientists said.
Scientists
studying radiation in the rings of Saturn also found evidence of oxygen. Doug
Hamilton of the University of Maryland said the main radiation belts in the
rings are comprised mostly of oxygen and water.
"That
is most likely the result of the bombardment of the planet's rings and icy
moons by the radiation trapped in Saturn's magnetic field," Hamilton said.
Molecular
oxygen has also been found above the icy Galilean moons of Jupiter.
Working
in coordination with Hamilton's group, a group of scientists at the Applied
Physics Laboratory at Johns Hopkins University found an unexpected radiation
belt in the D ring. And they learned that the radiation belts of Saturn are
more intense on the night-side of the planet.
Invisible
moon?
Images
of the narrow Keeler gap in Saturn's A ring offer circumstantial evidence
of an unseen moon.
The Keeler
gap is narrow, only 26 miles (42 kilometers) wide. Several faint discontinuities, or spikes, in
the outer edge of the gap have been discovered and are similar to spikes seen
in the core of the inner F ring, which is home to the moon Prometheus.
Based
on the similarity to the features caused by Prometheus in the F ring, it is
likely that the newly discovered features are the product of the passage of
a yet-unseen moonlet on an eccentric orbit within the Keeler gap.
The tiny moon would have a diameter of only a few miles. It was first
reported last November.
New
ring phenomena
An assortment
of new ring phenomena was observed on the dark side of Saturn's rings immediately
after Cassini entered orbit. The new ring variations may be evidence of the
clumping and aggregation of ring particles, most likely caused by gravitational
effects of Saturn or other bodies.
Closer
looks at gravitational disturbances in the rings could lead to the discovery
of new ring-bound moons.
As the
particles comprising the rings orbit Saturn they pass through what are called
Pan wakes, wavy features seen in the outer edges of the A ring. They
are the result of the tiny moon's gravitational pull on the particles in this
ring.
As the
particles orbit through the Pan wakes, they are forced closer together than
normal and create a ropy appearance. Similar ropy features seen in other regions
of the rings could be evidence of hidden moons.
New
rings
Also,
several new faint rings have been spotted in new images from Cassini.
Many of these are in various gaps between other, larger rings and may
indicate the presence of tiny moons, either coincident with the ring or close
by. [NASA has a summary here.]
One ring,
which was reported earlier, lies in the same orbit as the small moon Atlas.
Porous
moons
Other
new data from the inner rings has yielded more reliable approximations of
the masses of two of Saturn's ring-bound moons, Atlas and Pan.
The research
implies the moons are very porous - similar to moons orbiting just outside
Saturn's rings. The low densities suggest
that all the inner moons and satellites were smaller bits and pieces that
were gravitationally pulled together; basically orbiting rubble piles.
Trojan
moon
Late last
year it was reported that researchers had found a new moon orbiting Saturn,
but recent findings suggest that it is instead a "Trojan moon."
Trojan
moons are companions to larger moons. In
this case, the 3-mile-wide (5-kilometer) Polydeuces orbits Saturn in lockstep
with the larger moon Dione.
More
to come
The deluge
of images and data from Cassini will continue for the next three-plus years.
Early in March, the orbiter will swing past Enceladus, whose surface
is relatively young - 100 million years or so - and has many interesting features.
The ice
that coats it is especially clean, and gives the moon the highest albedo,
a measure of light reflectivity, of any body in the solar system.
Enceladus has an albedo greater than 90 percent, whereas the Earth
and its moon have albedos of 38 percent and 12 percent, respectively.
advertisement
