[meteorite-list] The (Long) Weekend Warrior: Nine Moons, 62 Hours (Cassini)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 19 Oct 2010 15:23:54 -0700 (PDT)
Message-ID: <201010192223.o9JMNss6018264_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-341

The (Long) Weekend Warrior: Nine Moons, 62 Hours
Jet Propulsion Laboratory
October 19, 2010

Taking a long-weekend road trip, NASA's Cassini spacecraft successfully
glided near nine Saturnian moons, sending back a stream of raw images as
mementos of its adrenaline-fueled expedition. The spacecraft sent back
particularly intriguing images of the moons Dione and Rhea.

The Dione and Rhea pictures are the highest-resolution views yet of
parts of their surfaces. The views of the southern part of Dione's
leading hemisphere (the part of the moon that faces forward in its orbit
around Saturn) and the equatorial region of Rhea's leading hemisphere
are more detailed than the last time we saw these terrains with NASA's
Voyager spacecraft in the early 1980s.

Of the five big icy moons of Saturn, Dione and Rhea are often considered
a pair because they orbit close to each other, are darker than the
others, and exhibit similar patterns of light reflecting off them. These
new images, however, highlight the differences between these sister moons.

Both images show similar geographic regions on each satellite. However,
scientists can identify differences in geological histories of the two
bodies from differences in the numbers and sizes of visible craters on
their surfaces. The number and size of craters on a body's surface help
indicate the age of that surface - the more craters there are and the
larger they are, the older the surface is.

Rhea, for example, shows ancient, intense bombardments throughout this
region. However, the same region of Dione is divided into distinct areas
that exhibit variations in the number and size of preserved craters. In
particular, while parts of Dione are heavily cratered like Rhea, there
are other areas covered by relatively smooth plains. Those areas have
many small craters, but few large impact scars, which indicates that
they are geologically younger than the heavily cratered areas. The
smooth plains must have been resurfaced at some point in Dione's past --
an event that seems to be missing from Rhea's geological history on this
side of the moon.

Images of the moon Mimas, captured just before it went into shadow
behind Saturn, will be compared to thermal maps made earlier this year
that showed an unexpected "Pac-Man" heat pattern. (See for more details.
<http://www.jpl.nasa.gov/news/news.cfm?release=2010-103>)

Cassini also caught a picture of the tiny, 4-kilometer-wide
(3-mile-wide) moon Pallene, in front of the planet Saturn, which is more
than 120,000 kilometers (75,000 miles) wide at its equator.

Cassini's elliptical orbital pattern around Saturn means it can target
moons for flybys about once or twice a month. The flybys on this
particular Cassini road trip were "non-targeted" flybys, meaning
navigators did not refine Cassini's path to fly over particular points
on each moon.

Cassini's long weekend started on Thursday, Oct. 14, at 5:07 p.m. UTC
(9:07 a.m. PDT), when it passed by Saturn's largest moon Titan at an
altitude of 172,368 kilometers (107,104 miles) above the surface. Then
came a whirlwind 21 hours in which Cassini flew by Polydeuces at 116,526
kilometers (72,406 miles), Mimas at 69,950 kilometers (43,465 miles),
Pallene at 36,118 kilometers (22,443 miles), Telesto at 48,455
kilometers (30,109 miles), Methone at 105,868 kilometers (65,783 miles),
Aegaeon at 96,754 kilometers (60,120 miles) and Dione at 31,710
kilometers (19,704 miles). Cassini's last visit -- Rhea at 38,752
kilometers (24,079 miles) ??? took place at 6:47 a.m. UTC on Oct. 17
(10:47 p.m. PDT on Oct. 16).

Scientists decided in advance which observations they wanted to make
while the spacecraft was cruising past all the moons. They chose to
obtain images of Titan, Mimas, Pallene, Dione and Rhea. They also
obtained thermal scans of Mimas, Dione and Rhea.

For more raw images, visit: http://saturn.jpl.nasa.gov/photos/raw/ .

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. The Jet Propulsion
Laboratory manages the project for NASA's Science Mission Directorate in
Washington. The Cassini orbiter was designed, developed and assembled at
JPL. The imaging operations center is based at the Space Science
Institute in Boulder, Colo.

More Cassini information is available, at t http://www.nasa.gov/cassini
<http://www.nasa.gov/cassini>and http://saturn.jpl.nasa.gov.

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui.c.cook at jpl.nasa.gov

2010-341
Received on Tue 19 Oct 2010 06:23:54 PM PDT