NASA orbiter spots strange 'hidden' red bands on Saturn moon

Thursday, July 30, 2015, 1:36 PM - NASA's Cassini spacecraft recently captured images of Saturn's small moon, Tethys, revealing strange, mysterious red bands on the surface.

Saturn's moons are strange and wonderful worlds, and NASA's Cassini orbiter has presented us with a multitude of unparalleled images of these satellites as they orbit the ringed planet.

The spacecraft's cameras are equipped to capture images from a wide range of the spectrum of light. By combining images taken with red, green and blue filters, the mission team has produced spectacular colour views of the planet and its moons, revealing their appearance if we were actually there, looking at them with our own eyes.

Other filters have given the scientists a much broader look at these objects, though, and they get even more strange and wonderful with each image.

In the case of Tethys - Saturn's 5th largest moon, shown to the right - these "naked eye" images simply reveal a cratered, fairly uniformly-gray surface, where the 400-km wide Odysseus crater is likely the only feature that really captures the attention.

Draw in more of the spectrum of light, though - infrared and ultraviolet - and "hidden" colours jump out. This has revealed a yellowish cast to portions of the moon, which transitions to nearly pure white in other regions.

According to the Cassini team, the white comes from ice particles freshly deposited on the leading hemisphere of the moon as it sweeps through Saturn's diffuse E-ring, while the yellow is due to Saturn's radiation belt bombarding the trailing hemisphere and causing chemical reactions with the surface ice.

The Inner Saturn System. Credit: NASA/JPL-Caltech

In the most recent close-up views of the moon, though, strange red bands - hidden from the human eye but showing up quite vividly when infrared and ultraviolet light are included - are giving the team a bit of a mystery to solve.

Closeup of Tethys' surface, combining clear, infrared, green and ultraviolet filtered images. Credit: NASA/JPL-Caltech

According to NASA:

A few of the red arcs can be seen faintly in observations made earlier in the Cassini mission, which has been in orbit at Saturn since 2004. But the color images for this observation, obtained in April 2015, are the first to show large northern areas of Tethys under the illumination and viewing conditions necessary to see the arcs clearly. As the Saturn system moved into its northern hemisphere summer over the past few years, northern latitudes have become increasingly well illuminated. As a result, the arcs have become clearly visible 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."

Cutting across both plain and crater alike, the bands likely formed more recently than the surrounding surface features, but according to the Cassini team, the origin of these bands is unknown.

Furthermore, the only other object in the Saturn system that apparently also shows red-tinged features is Dione, Tethys' neighboring moon. Elsewhere in the solar system, red shows up on the surfaces of Jupiter's moon Europa (perhaps as a result of the mixture of salts and sulfur compounds), and was spotted at the north pole of Pluto's moon, Charon (possibly due to some of Pluto's methane and nitrogen atmosphere being deposited there).

While it is possible that these red bands are more common on Tethys than we realize, and they are simply covered over fairly quickly by ice deposited on the surface, closer, higher-resolution images scheduled for later this year may tell us more.

"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 NASA's Jet Propulsion Laboratory.

Source: NASA