A new image released by NASAís Jet Propulsion Laboratory shows an incredible new surface feature discovered on Saturnís icy moon of Tethys: enormous, red arcs that span most of the moonís northern hemisphere. Theyíre strikingly obvious, even from space, and scientists involved with the Cassini probe which took the pictures have no clear idea of what they are, or what causes them. There are ideas, of course, but for now the red streaks of Tethys are one of our solar systemís most galling mysteries.
Cassini first took detailed pictures of the arcs in April, surveying the moon now that its northern half has moved into its summer phase and is thus bright enough for real investigation. It took a variety of pictures at different wavelengths, then combined them in the false-color image embedded below. The arcs really are red, and they really do stand out from the color of the surface around them, but the harsh red-grey distinction has been intensified to make the arcs easier to see.
NASA will use Cassini to take more detailed readings of the Tethys surface in November, which should grant more insight into the nature of these enormous features. Until then, scientists can only speculate ó and speculate they have!
Red like this is somewhat unusual in the Saturn system. Itís indicative of a number of possible chemicals ó none of them known to be abundant in the area. Itís possible that they are the result of contamination of ice, but the question remains: contaminated with what, exactly? And is that contamination streaked across the surface like this? Geographically young surfaces, like Jupiterís Europa sometimes display this sort of red coloration, but the streaked pattern is still mysterious.
One possible explanation is outgassing, in which a moon (or asteroid, or comet) squirts enormous volumes of gas out of a heated, pressurized interior. Tethys is going into its summer, as mentioned, and it could be that these arcs will be gone in short order ó a form of surface contamination that marks the passing of Tethynian (?) seasons. Itís been theorized that these streaks were noticed when illumination of the surface made them visible, but perhaps they werenít visible before because they simply didnít exist without that extra solar heat to create them.
Tethys, zoomed out, and without the color correction. Credit: NASA/JPL
There are other ideas, however. The resolution of these pictures still leaves a lot to the imagination, as every pixel in the above image stands in for an area about 2,300 feet (700 meters) across. Itís possible that the red material is coming from below the surface, via fractures that are too small to be detected at that level of detail.
Interestingly, the same color-enhancement process that makes the red streaks more visible has also tinted the left section of the image a yellowy color. Thatís because the radiation from Saturnís magnetosphere is constantly slamming into this particular hemisphere of the moon, modifying it chemically. This wouldnít be visible to the naked eye, but with color filtering in place we see that Tethys has actually be planet-burned by its proximity to a gas giant.
Edited by Night Hunter, 07 August 2015 - 06:51 PM.