Cassini Flyby of Saturn Moons Zooms in on Puzzling Red Streaked Tethys

Summary: The 2015 Cassini flyby of Saturn moons reveals puzzling images of red streaked Tethys, LPI's Paul Schenk says Dec. 15 at AGU's annual fall meeting.

Unusual red streaks arc across pitted surface of Saturn's ice-rich Tethys moon, as revealed by enhanced color mosaic of Cassini Flyby's imaging observations of Tethys' northern areas, April 2015: NASA/JPL-Caltech/Space Science Institute, Public Domain, via NASA Jet Propulsion Laboratory

On Tuesday, Dec. 15, at the American Geophysical Union’s annual meeting in San Francisco, Lunar and Planetary Institute staff scientist Paul Schenk says Saturn’s red streaked Tethys moon baffles scientists, who are studying images captured by Cassini’s Saturn Flyby in April and November 2015.

Three prominent sets of red arcs blaze across the cratered terrain of Tethys’s northern latitudes. Five to 10 parallel lines, known geologically as lineations, make up each set. The curvilinear markings are narrow, with widths of only a few kilometers, but are lengthy, logging distances of 50 to 250 kilometers (31 to 155 miles) or more.

Tethys’s heavily cratered terrain does not deflect the red lines. In the northwestern hemisphere, arcs undauntedly plumb the 10 kilometer (6.2 mile) depths of the floor of the Odysseus basin. After spanning the 400 kilometer (almost 250 miles) diameter of Tethys’s largest impact crater, the lines continue their mysterious trail.

Apart from faint discolorations and small dark spots in the vicinity, no obvious landforms appear to be associated with the telltale streaks. Cassini’s current resolution reveals about 25 small dark spots with diameters of 200 to 800 meters (656 to 2,625 feet). The spots present low reflectivity, known as albedo, and their sharp boundaries do not exhibit the raised rims associated with impact origin. Fifteen, or about 60 percent, of the spots are located at the bottom of small craters.

Particles from Saturn’s E ring, the planet’s second outermost ring, generally accumulate on the ring’s orbiting moons. Infalling E ring particles contribute a bluish tint to Tethys’s equator. The visibility of the dark spots and of the red arcs, free from dusty smudgings, seems to indicate their recent activeness.

Paul Schenk’s AGU abstract states: “The coloration, global pattern and collocated dark spots are consistent with recent/active alteration of the surface, given that E-ring accumulation is expected to remove intrinsic color signatures in a geologically short time period.”

Tethys’s mysterious red arcs stand out as fairly rare in Saturn’s clutch of 62 known moons and also as unusual in the solar system. A few reddish small craters on Dione serve as the only other instance of reddish tinted lunar features. Elsewhere in the solar system, only Europa, one of Jupiter’s 63 known moons, yields a crisscross of lines as red-tinted landforms.

The 2015 images of Tethys (TEE-thiss) are clearer than 2004’s images because of increasing illumination of the ice-rich moon’s northern latitudes with the Saturn system’s passage into its northern hemisphere summer.

Although Tethys’s surface displays a fairly uniform natural color, Cassini’s images use clear, green, infrared and ultraviolet spectral filters to highlight color nuances at wavelengths invisible to human eyes. Alteration of the lunar surface by high-energy particles from Tethys’s host planet’s magnetosphere account for yellowish tones. The change in Tethys’s appearance that is detected in enhanced-color views results from chemical modification of the moon’s surface by the bombardment of Saturn’s high-energy particles.

The clear image of red streaked Tethys captured April 11, 2015, by Cassini covers an area of 490 by 415 kilometers (305 by 258 miles), at 30 degrees north latitude, 187 degrees west longitude. The original resolution is about 700 meters (2,300 feet) per pixel.

Cassini’s Flyby images confirm the puzzle of red streaked Tethys.

“It’s clearly painted on the surface in some way that we do not as yet understand,” says Paul Schenk. “We basically have a little mystery.”

True polar wander (TPW) or non-synchronous rotation (NSR)?: James Tuttle Keane @jtuttlekeane via Twitter Dec. 15, 2015

Acknowledgment

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

Image credits:

Tethys’s red streaks: NASA/JPL-Caltech/Space Science Institute, Public Domain, via NASA Jet Propulsion Laboratory @ http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA19637

True polar wander (TPW) or non-synchronous rotation (NSR)?: James Tuttle Keane‏ @jtuttlekeane via Twitter Dec. 15, 2015, @ https://twitter.com/jtuttlekeane/status/676819566131937280

For further information:

Drake, Nadia. "The Curious Case of the Blood-Stained Moon." National Geographic Phenomena > No Place Like Home. Dec. 15, 2015.
Available @ http://phenomena.nationalgeographic.com/2015/12/15/the-curious-case-of-the-blood-stained-moon/

GeoBeats News. "Icy Moon Of Saturn Has Mysterious Red Arcs On Its Surface." YouTube. July 30, 2015.
Available @ http://www.youtube.com/watch?v=QpBv9yc-B0Q

James Tuttle Keane‏ @jtuttlekeane. "The 'bloody streaks' on Tethys are symmetric about tidal axis- suggesting TPW or NSR? (P21B-02 Paul Schenk) #AGU15." Twitter. Dec. 15, 2015.
Available @ https://twitter.com/jtuttlekeane/status/676819566131937280

"Red Arcs on Tethys." NASA Jet Propulsion Laboratory California Institute of Technology > Images. July 29, 2015.
Available @ http://www.jpl.nasa.gov/spaceimages/details.php?id=PIA19637

Schenk, Paul. "P21B-02:"'Blood Stains' on Tethys: Evidence for Recent Activity?" AGU Abstract.
Available @ https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/67320