[meteorite-list] Cassini Probe Spies Spokes in Saturn's Rings

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Sep 15 12:28:25 2005
Message-ID: <200509151627.j8FGRFU06375_at_zagami.jpl.nasa.gov>

http://space.com/scienceastronomy/050915_cassini_spokes.html

Cassini Probe Spies Spokes in Saturn's Rings
By Tariq Malik
space.com
15 September 2005

The Cassini spacecraft orbiting Saturn has finally spotted spokes
cutting across the planet's rings, a phenomenon astronomers have long
hoped their plucky orbiter might find.

While flying past the dark side of Saturn's B ring, Cassini's camera eye
photographed the spokes - which appear as radial markings - in a series
of three images taken over about 27 minutes. The find is a gem of sorts
for mission imaging scientists, who have been hunting for the ring
spokes since Cassini arrived at Saturn.

"We've been on the lookout for them since February, 2004," said Carolyn
Porco, Cassini imaging team leader at the Space Science Institute in
Boulder, CO, of the spokes in an e-mail interview. "Spokes are one of
those Saturn-system phenomena that we are keenly interested in
understanding."

Saturn's odd ring spokes were first discovered during NASA's Voyager
mission, which swung passed the planet in the 1980s, and later observed
by astronomers using the Hubble Space Telescope.

But spokes were noticeably absent
<http://www.space.com/scienceastronomy/cassini_saturn_040227.html> when
Cassini made its final approach toward Saturn in February 2004, and are
a prime target for astronomers because their role and formation within
the planet's rings are not fully understood.

"These are among the things we hope to learn," said Porco, who
participated in the Voyager mission as well. "[The spokes] are
obviously related to a host of processes - and may point to some important
effects in understanding the magnetic field and the planet's
magnetosphere, and how these systems interact with the rings and
atmosphere."

Porco and her imaging team did not initially expect to observe ring
spokes until about 2007, when certain models predicted spoke formation
and visibility.

"Well, in some sense we should have expected, if the recent models are
correct, to see them on the dark side where the photoelectron abundance
is low," Porco said of the spokes. "So, I was surprised to see them. But
once they showed up, I realized we should have expected them there all
along."

While the images were released on Sept. 13, Cassini actually
photographed the ring spokes on Sept. 5, 2005, using clear filters and
its wide-angle camera from a distance of about 198,000 miles (318,000
kilometers) from Saturn. The spokes themselves are fairly faint, and are
about 60 miles (100 kilometers) wide and 2,200 miles (3,500 kilometers)
long, researchers said.

Unlike Voyager or Hubble, Cassini is in a unique position to study ring
spoke phenomena at Saturn, Porco said.

"Remember, Voyager was just a flyby, Cassini is in orbit," Porco said,
adding that Cassini is a vastly superior observation platform when
compared to Voyager. "We have the opportunity for monitoring them and
their behavior, their comings and goings, how they evolve, when they
appear and disappear."

By observing the spokes on the dark side of Saturn's rings, Cassini
recreated a bit of space exploration history. Its predecessor, Voyager,
also first observed the ring spoke phenomena while photographing the
unilluminated side of the Saturn's rings.

"It felt like the old days, when we first saw the spokes," Porco said.
"They are one weird phenomena and it was a joy to see them
again - especially since we hadn't seen them yet and were eager to know
why."
Received on Thu 15 Sep 2005 12:27:14 PM PDT