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Cassini spots unusual red arcs on surface of Tethys

Red Streaks across the surface of Tethys NASA JPL Caltech Space Science Institute 2 photo posted on SpaceFlight Insider - Copy

Unusual arc-shaped, reddish streaks cut across the surface of Saturn’s ice-rich moon Tethys in this enhanced color mosaic. The red streaks are narrow, curved lines on the moon’s surface, only a few miles (or kilometers) wide but several hundred miles (or kilometers) long. Image and CaptionCredit: NASA / JPL-Caltech / Space Science Institute

NASA’s Jet Propulsion Laboratory, located at the California Institute of Technology, recently released color-enhanced images sent by the Cassini Spacecraft. They show mysterious reddish streaks on the surface of Saturn’s icy moon Tethys. The unusual red streaks are narrow, curved arcs a few miles wide and several hundred miles long. 

The enhanced color images, taken using a composite of clear, green, infrared, and ultraviolet spectral filters, highlight subtle and unusual color differences on the moon’s surface.

Tethys was discovered and named in 1684 by Giovanni Domenico Cassini, the Cassini spacecraft’s namesake. It has the lowest density of any moon in the Solar System and is made primarily of water ice with just a small fraction of rock.

NASA Cassini space image of Saturn's moon Tethy's Image Credit NASA JPL Caltech posted on SpaceFlight Insider

Cassini has been exploring Saturn and its many moons since arriving at the gas giant in 2004. Image Credit: NASA / JPL-Caltech / Space Science Institute

A few red streaks were first observed on its surface during a previous flyby made by Cassini but were too faint to make out. In recent years, as Saturn has moved into its northern hemisphere summer, the area where these streaks were observed have become better illuminated. As a result, in April of 2015, Cassini was able to send back clear images of red streaks for the first time.

“The red arcs really popped out when we saw the new images,” said Cassini participating scientist Paul Schenk of the Lunar and Planetary Institute in Houston. “It’s surprising how extensive these features are.”

Cassini scientist have been unable to determine the origin of the mysterious red streaks on its surface. Some possible explanations for the streaks theorize that they are a result of outgassing from inside the moon, that the reddish material may be exposed ice with chemical impurities, or that the streaks may be associated with fractures on the moon’s surface that may be out of the resolution of the available images.

“The red arcs must be geologically young because they cut across older features like impact craters, but we don’t know their age in years,” said Paul Helfenstein, a Cassini imaging scientist at Cornell University, Ithaca, New York, who helped plan the observations. “If the stain is only a thin, colored veneer on the icy soil, exposure to the space environment at Tethys’ surface might erase them on relatively short time scales.”

Though reddish features can also be observed on the surface of Jupiter’s moon Europa, they remain rare in the Saturnian system. With the exception being a few small craters on the surface of another of Saturn’s moons – Dione.

Follow-up observations of the features are currently being planned for later this year, this time at a higher resolution.

“After 11 years in orbit, Cassini continues to make surprising discoveries,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “We are planning an even closer look at one of the Tethys red arcs in November to see if we can tease out the source and composition of these unusual markings.”

The Cassini-Huygens mission is a joint project of NASA, the European Space Agency (ESA), and the Italian Space Agency. The mission is managed by NASA’s Jet Propulsion Laboratory (JPL) out of the California Institute of Technology. The spacecraft was launched atop a Titan IVB/Centaur on October 15, 1997, and reached SOI (Saturn Orbit Insertion) in June of 2004. Since then, the spacecraft has spent 11 years in orbit around Saturn studying the planet, its rings, and its moons.


College student and long time space enthusiast, Jose has been a constant visitor to Cape Canaveral since he moved to central Florida. He joined the SFI team in the hopes of becoming more involved in the coverage of spaceflight and space exploration.

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More outstanding work from JPL and the Cassini team!

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