Tethys is one of the medium-sized moons of Saturn, discovered by well-known astronomer G.D. Cassini in 1684. Now, astronomers have discovered highly-unusual red arcs spreading across the surface of this frozen satellite.
The red streaks on Tethys are hundreds of miles in length, but only a few miles across. They were first spotted in enhanced-color images from the Cassini craft. These images were compiled from observations taken in ultraviolet and infrared light, in addition to unaltered visible light and using a green filter. This combination brings out subtle color differences that would remain unseen by the unaided human eye.
Tethys is titled in honor of the mythical Titan of the same name.
"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," Paul Helfenstein from Cornell University, a Cassini imaging scientist who assisted in the planning of this mission, said.
The Cassini observatory also imaged a bright basin on Tethys like never before, nearly simultaneously with the discovery of the mysterious bright red arcs.
Tethys has the lowest density of all known satellites in the Solar System — less than that of water. This unusual property is also the case for its parent world. Many astronomers like to say that if one could find a bathtub large enough and filled it with water, Saturn would float.
Tethys has been explored previously by several other spacecraft. Before Cassini arrived at the system in 2004, the moon was visited by Pioneer 11 in 1979, Voyager 1 in 1980 and Voyager 2 the following year. However, Cassini is the first spacecraft to orbit around the second-largest planet in our solar system.
Odysseus, a brightly-colored massive impact crater, was imaged by Cassini like never before due to the multi-wavelength imaging technique. This basin measures 280 miles across a moon with a diameter of just around 660 miles. The impact that formed Odysseus likely played a vital role in the formation of the geologically-fascinating satellite. A new photo of the crater was taken by Cassini from a distance of 186,000 miles.
The Cassini mission is drawing to a close, as the spacecraft has spent a decade exploring Saturn and its attendant satellites. As part of a daring maneuver, mission planners will soon direct the vehicle to race through the space between Saturn's rings and the outskirts of the planetary atmosphere.
"After 11 years in orbit, Cassini continues to make surprising discoveries. 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," said Linda Spilker, Cassini project scientist at Jet Propulsion Laboratory.
