JPL: Cassini Finishes Sleigh Ride by Icy Moons

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JPL: Cassini Finishes Sleigh Ride by Icy Moons

Post by bystander » Wed Dec 22, 2010 3:12 am

Cassini Finishes Sleigh Ride by Icy Moons
NASA JPL | Cassini Solstice Mission | 21 Dec 2010
On the heels of a successful close flyby of Saturn's moon Enceladus, NASA's Cassini spacecraft is returning images of Enceladus and the nearby moon Dione.
Several pictures show Enceladus backlit, with the dark outline of the moon crowned by glowing jets from the south polar region. The images show several separate jets, or sets of jets, emanating from the fissures known as "tiger stripes." Scientists will use the images to pinpoint the jet source locations on the surface and learn more about their shape and variability.

The Enceladus flyby took Cassini within about 48 kilometers (30 miles) of the moon's northern hemisphere. Cassini's fields and particles instruments worked on searching for particles that may form a tenuous atmosphere around Enceladus. They also hope to learn whether those particles may be similar to the faint oxygen- and carbon-dioxide atmosphere detected recently around Rhea, another Saturnian moon. The scientists were particularly interested in the Enceladus environment away from the jets emanating from the south polar region. Scientists also hope this flyby will help them understand the rate of micrometeoroid bombardment in the Saturn system and get at the age of Saturn's main rings.

This flyby of Enceladus, the 13th in Cassini's mission, took a similar path to the last Enceladus flyby on Nov. 30.

About eight hours before the Enceladus flyby, Cassini also swung past Dione at a distance of about 100,000 kilometers (62,000 miles). During that flyby, the spacecraft snapped clear, intriguing images of the bright, fractured region known as the "wispy terrain." These features are tectonic ridges and faults formed by geologic activity on the moon sometime in the past. Scientists will now be able to measure the depth and extent of them more accurately.

Enceladus Rev 142 Raw Preview
Mimas wanders in to view
Planetary Society Blog | Emily Lakdawalla | 21 Dec 2010
Enceladus and Mimas

As Cassini approached for its close flyby of Enceladus on December 20, 2010, it caught Mimas passing through the field of view. The Sun was nearly in front of Cassini so both moons are lit only as very skinny crescents; the lighting highlights Enceladus' plumes, and shines off of tiny particles in the E ring, which provides a lighter backdrop to the dark night sides of both moons. Mimas and Enceladus are actually very similar in size, but Enceladus was much closer to Cassini when the photo was taken.

Credit: NASA/JPL/SSI/Emily Lakdawalla
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Re: JPL: Cassini Finishes Sleigh Ride by Icy Moons

Post by neufer » Wed Dec 22, 2010 3:24 am

bystander wrote:Cassini Finishes Sleigh Ride by Icy Moons
NASA JPL | Cassini Solstice Mission | 21 Dec 2010

Mimas wanders in to view
Planetary Society Blog | Emily Lakdawalla | 21 Dec 2010
Enceladus and Mimas

As Cassini approached for its close flyby of Enceladus on December 20, 2010, it caught Mimas passing through the field of view. The Sun was nearly in front of Cassini so both moons are lit only as very skinny crescents; the lighting highlights Enceladus' plumes, and shines off of tiny particles in the E ring, which provides a lighter backdrop to the dark night sides of both moons. Mimas and Enceladus are actually very similar in size, but Enceladus was much closer to Cassini when the photo was taken.

Credit: NASA/JPL/SSI/Emily Lakdawalla
[img3="This graph was created in June 2007 using all asteroids with "well-determined" orbits (specifically, 156929 numbered asteroids)."]http://ssd.jpl.nasa.gov/images/ast_histo.png[/img3]
What I find most interesting (and useful to remember)
are the number of neighboring bodies near a 5:2 resonance:
  • Enceladus & A Ring orbital periods are in a ratio of ~5:2

    Mimas & B Ring orbital periods are in a ratio of ~5:2

    -----------------------------------------------------------------------------------
    Saturn & Jupiter orbital periods are in a ratio of ~77:31
    or just (154/155)ths shy of a narrow 5:2 'Kirkwood gap' resonance.

    Jupiter & Ceres orbital periods are in a ratio of ~47:19
    or just (94/95)ths shy of a narrow 5:2 'Kirkwood gap' resonance.

    Ceres & Mars orbital periods are in a ratio of ~22:9
    or just (44/45)ths shy a narrow 5:2 'Kirkwood gap' resonance.


    Venus & Mercury orbital periods are in a ratio of ~23:9
    or just (46/45)ths past a narrow 5:2 'Kirkwood gap' resonance.

    -----------------------------------------------------------------------------------
Is the predominance of 5:2 resonances (corresponding to ~ 54.3% orbital ratios)
between neighboring bodies responsible, in part, for the Titius-Bode approximation?
Art Neuendorffer

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