Cassini Spacecraft Shows Saturnian Moon Tethys as Icy Float Amid Rings

Summary: Cassini spacecraft shows Saturnian moon Tethys as an icy float amid rings in an image released Monday, Feb. 8, by NASA.

"Ices and Shadows" image of Tethys as icy float in Saturnian system; image obtained Monday, Nov. 23, 2015, by Cassini spacecraft; image addition date 2016-02-08; image credit NASA/JPL-Caltech/Space Science Institute: "PIA18355 Ices and Shadows," May be used for any purpose without prior permission, via NASA JPL Photojournal

An image released by the National Aeronautics and Space Administration (NASA) Monday, Feb. 8, 2016, via the Cassini spacecraft shows Saturnian moon Tethys as an icy float amid the gas giant planet’s prominent ring system.

“Saturn’s moon Tethys appears to float between two sets of rings in this view from NASA’s Cassini spacecraft, but it’s just a trick of geometry,” states the image’s accompanying news release. “The rings, which are seen nearly edge-on, are the dark bands above Tethys, while their curving shadows paint the planet at the bottom of the image.”

The image comes from NASA’s growing archive of visual captures of the Solar System’s second largest planet by the Cassini spacecraft. The unmanned spacecraft’s wide-angle camera is credited with taking the unusual portrait of Tethys in visible light Monday, Nov. 23, 2015, at a distance of approximately 40,000 miles (65,000 kilometers). The image scales 2.4 miles (4 kilometers) per pixel. North is up in this view of Saturnian moon Tethys.

Tethys numbers among 53 natural satellites and nine provisional moons in the Saturnian system. The surface of heavily cratered Tethys is composed mainly of water ice, also the main material in Saturn’s vast ring system.

Tethys (pronounced TEE-this or TEH-this) has a diameter of 660 miles (1,062 kilometers). The Odysseus impact basin stands out in Cassini’s image as the bright, large circle on the top right portion of the Saturnian moon. The gigantic impact basin measures a diameter of 280 miles (450 kilometers). Cassini mission scientists suggest that the composition or structure of the terrain uncovered by the impact may account for the basin’s distinctive brightness. As Saturn’s second most illuminated moon, Tethys presents a bright, neutral surface.

As with many of the Solar System’s moons, Saturnian moon Tethys maintains one face toward its host planet and keeps the other face pointed away. The anti-Saturn face appears as Tethys’s right side in Cassini’s “Ices and Shadows” portrait of Tethys.

"Crescent Tethys and Rings" image, taken by Cassini's wide-angle camera Tuesday, Aug. 18, 2015, at a distance of 184,000 miles (296,000 kilometers); reflected light from Saturn's rings dimly illuminates the planet's northern hemisphere (upper left); image addition date 2015-12-07; image credit NASA/JPL-Caltech/Space Science Institute: "PIA18348 Crescent Tethys and Rings," May be used for any purpose without prior permission, via NASA JPL Photojournal

A Cassini image released Tuesday, Dec. 8, 2015, by NASA reveals a rare view of Tethys as a bright crescent, with its anti-Saturn face shrouding most of the Saturnian moon’s surface. The image was taken in visible light Aug. 18, 2015, by Cassini's wide-angle camera. Cassini was distanced approximately 184,000 miles (296,000 kilometers) from Tethys.

The companion news release describes the image, “Crescent Tethys and Rings,” as a snapshot of Tethys as “an elegant crescent” that is “dwarfed by the scale of Saturn and its rings.” The image captures a unique view of Tethys. "Views like this are impossible from Earth, where we only see Saturn's moons as (more or less) fully illuminated disks," editor Tony Greicius explains.

Gravity is responsible for Tethys’s spherical shape. Tethys is sized sufficiently for its own gravity to mold the Saturnian moon into a sphere by overcoming the material strength of its composite materials.

A Cassini image, "Janus and Tethys," released Tuesday, Jan. 19, 2016, by NASA contrasts Tethys with small Saturnian Janus. The image was taken in visible green light Oct. 27, 2015, by Cassini's narrow-angle camera. Cassini was distanced approximately 593,000 miles (955,000 kilometers) from Janus and 810,000 miles (1.3 million kilometers) from Tethys.

With a diameter of 111 miles (179 kilometers), heavily cratered Janus measures about one-sixth of Tethys’s width. Janus’s irregular shape derives from its lacking enough massiveness for sphere formation by gravity.

The Cassini spacecraft has been demystifying the Saturnian system since the unmanned spacecraft’s arrival June 30, 2004, at the sixth planet from the sun. In June 2008 Cassini began the Cassini Equinox Mission as its first mission extension. Since September 2010, Cassini has been involved in its second mission extension, known as the Cassini Solstice Mission.

Cassini’s scheduled flyby of largest Saturnian moon Titan Tuesday, Nov. 29, 2016, Cassini serves as gateway to F-Ring orbits and to Cassini’s Grand Finale mission phase in 2017.

The Cassini mission is a cooperative project of the European Space Agency (ESA), the Italian Space Agency (Agenzia Spaziale Italiana ASI) and NASA. The Pasadena, California-based Jet Propulsion Laboratory, a division of the California Institute of Technology, manages the Cassini mission for NASA’s Science Mission Directorate, headquartered in Washington, D.C.

Janus (right) and Tethys (left) epitomize main difference of shape that distinguishes small from large moons; image taken Tuesday, Oct. 27, 2015, by Cassini spacecraft's narrow angle camera; image addition date 2016-01-18; image credit NASA/JPL-Caltech/Space Science Institute: "PIA18353: Janus and Tethys," May be used for any purpose without prior permission, via NASA JPL Photojournal

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

"Ices and Shadows" image of Tethys as icy float in Saturnian system; image obtained Monday, Nov. 23, 2015, by Cassini spacecraft; image addition date 2016-02-08; image credit NASA/JPL-Caltech/Space Science Institute: "PIA18355 Ices and Shadows," May be used for any purpose without prior permission, via NASA JPL Photojournal @ https://photojournal.jpl.nasa.gov/catalog/PIA18355;
"Ices and Shadows," NASA image article, Feb. 8, 2016, Generally not subject to copyright in the United States, via NASA @ https://www.nasa.gov/image-article/ices-shadows/; "Ices and Shadows," NASA image article, Feb. 8, 2016, Generally not subject to copyright in the United States, via NASA @ http://www.nasa.gov/image-feature/jpl/pia18355/ices-and-shadows

"Crescent Tethys and Rings" image, taken by Cassini's wide-angle camera Tuesday, Aug. 18, 2015, at a distance of 184,000 miles (296,000 kilometers); reflected light from Saturn's rings dimly illuminates the planet's northern hemisphere (upper left); image addition date 2015-12-07; image credit NASA/JPL-Caltech/Space Science Institute: "PIA18348 Crescent Tethys and Rings," May be used for any purpose without prior permission, via NASA JPL Photojournal @ https://photojournal.jpl.nasa.gov/catalog/PIA18348;
"Crescent Tethys and Rings," NASA image article, Dec. 8, 2015, Generally not subject to copyright in the United States, via NASA @ http://www.nasa.gov/image-feature/jpl/pia18348/crescent-tethys-and-rings

Janus (right) and Tethys (left) epitomize main difference of shape that distinguishes small from large moons; image taken Tuesday, Oct. 27, 2015, by Cassini spacecraft's narrow angle camera; image addition date 2016-01-18; image credit NASA/JPL-Caltech/Space Science Institute: "PIA18353: Janus and Tethys," May be used for any purpose without prior permission, via NASA JPL Photojournal @ https://photojournal.jpl.nasa.gov/catalog/PIA18353;
"Janus and Tethys," NASA image article, Jan. 19, 2016, Generally not subject to copyright in the United States, via NASA @ http://www.nasa.gov/image-feature/jpl/pia18353/janus-and-tethys

For further information:

"Cassini-Huygens." NASA Jet Propulsion Laboratory > Missions > Mission to Saturn.
Available @ http://www.jpl.nasa.gov/missions/details.php?id=5866

GeoBeats News. "Saturn Towers Over Its Moon In Striking NASA Image." YouTube. Jan. 16, 2016.
Available @ http://www.youtube.com/watch?v=-Mhrh9QjEcQ

Greicius, Tony, ed. "Bright Basin on Tethys." NASA Jet Propulsion Laboratory. July 27, 2015.
Available @ http://www.nasa.gov/jpl/pia18329/bright-basin-on-tethys

Greicius, Tony, ed. "Janus and Tethys." NASA. Jan. 19, 2016.
Available @ http://www.nasa.gov/image-feature/jpl/pia18353/janus-and-tethys

Marriner, Derdriu. "Cassini Flyby of Saturn Moons Zooms in on Puzzling Red Streaked Tethys." Earth and Space News. Wednesday, Dec. 16, 2015.
Available @ https://earth-and-space-news.blogspot.com/2015/12/cassini-flyby-of-saturn-moons-zooms-in.html

NASA Jet Propulsion Laboratory. "Cassini - The Grand Finale." NASA Jet Propulsion Laboratory Cassini: Mission to Saturn > downloadable items.
Available @ http://saturn.jpl.nasa.gov/files/Cassini_Grand_Finale_Fact_Sheet_508.pdf