The moon of Saturn Dione has strange stripes

The researchers suggest that the long straight parallel lines on the surface of the satellite could be excrement from the rings of Saturn, one of the moons or a comet passing by.

Dione sits in the center and above the rings of Saturn in this image of the Cassini spacecraft. The largest moon of Saturn, Titan, hides in the background, Pandora is on the right of the rings and Pan is the smallest point on the left.
NASA / JPL-Caltech / Institute for Space Science

The moons of Saturn are a hodgepodge of misfits. Iapetus looks like the death star of Star wars. Tiny Pan looks like a cosmic empanada. And now, something seems to be engraving strangely straight lines on the icy surface of Dione.

The lines – or linear virgae, to use the proposed technical term – to extend over hundreds of kilometers and yet less than 5 kilometers wide. They are all parallel to the equator and reside only at the lowest latitudes. They are brighter than anything around them and seem to be placed on existing elements such as ridges and craters, which means they have been set up quite recently. And we do not know yet how they got there.

"We do not really know how to get such straight lines," says Emily Martin (National Museum of Air and Space), co-author of an upcoming article describing the score obtained at the surface Letters of geophysical research. "Linear virgins do not really look like anything we see in the solar system."

This Cassini image shows some of the linear virgins (marked by green arrows) that cross the surface of Dione.
NASA / JPL-Caltech / Institute of Space Science / E.S. Martin and D.A. Patthoff, 2018

Moons are not foreign to distinctive surface markings. The moon of Saturn Enceladus has its famous tiger stripes, wavy ridges through which water gushes from an underground ocean. Neptune's Newt moon has dark streaks, probably marked by plume deposits. Debris lines move craters away throughout the solar system. Even our moon has festooned hollows carved by rocks that run down the hills.

Martin and co-author Alex Patthoff (Planetary Science Institute) have examined all these scenarios and others for Dione, but none seems to work. Dione's lines are too long, too broad, too light or too strangely placed.

The position parallel to the equator suggests that the most likely culprit is something that was already in the same plane as Dione's orbit and then gently rained on the surface.

This leaves only a few options. The material of the rings of Saturn could well be sprinkled, although it is not known which mechanism would drive it from the rings towards Dione. There may be a transfer of material from the Helene or Polydeuces satellites, the moons that share Dione's orbit. Or maybe the lines are debris from a comet that just passed.

"If we can find linear viruses elsewhere in the Saturn system, we can learn a little more about the sources of materials that can cover the surface of these moons," says Patthoff. "We do not have the ability to get more images yet, but we can explore all the image archives we have of Cassini."

Reference:

E. S. Martin and D. A. Patthoff. "Linear mysterious features through the moon of Saturn, Dione." Letters of geophysical research. October 15, 2018.