Shaping Dione

Dione_TectonicsThis image of Saturn’s moon Dione shows a mixture of features: bright, linear features showing evidence of tectonic movant and impact craters. The tectonic features reveal that Dione has been heated and cooled since its formation, and scientists use those as clues to piece together the moon’s past. The impact craters are evidence of external debris striking the surface and tell about the environment in which the moon has existed over its history.

Image Credit: NASA

A Summer Solstice Approaches

saturn askewCassini images of Saturn are generally oriented so that Saturn appears north up, but the spacecraft views the planet from all sorts of angles. Here, Saturn seems to sit askew as the tiny moon Dione looks on from lower left. The terminator, which separates night from day, is also tilted because the planet is nearing its northern summer solstice. As a result, the planet’s northern pole is in sunlight all throughout Saturn’s day.

Image Credit: NASA

Saturn and Methane

Saturn and MethaneThis picture of Saturn was made by the Cassini spacecraft at wavelengths of light that are absorbed by methane. The darker areas are regions where light travels further into the atmosphere, passing through more methane before being reflected off of clouds. The deeper the light goes, the more of it gets absorbed by methane, and the darker that part of Saturn appears.

The small moon just below the rings on the right is Dione.

Image Credit: NASA

Dione and Enceladus

Dione_EnceladusAlthough Saturn’s moons Dione (in the foreground) and Enceladus are made of more or less the same stuff, Enceladus has a considerably higher reflectivity than Dione. Therefore, it appears brighter against the blackness of space.

Enceladus has a constant rain of ice grains from its south polar jets which cover its surface with a bright snow. Dione’s older, weathered surface has slowly gathered dust and radiation damage, darkening through a process known as “space weathering.”

Image Credit: NASA

Dione Close Up

Dione chasmsSome parts of the surface of Saturn’s moon Dione are covered by linear features, called chasmata, in dramatic contrast to the round impact craters that cover most moons. The bright network of fractures on Dione was seen in poor resolution Voyager images and was called “wispy terrain.” The actual nature of this terrain was unclear until Cassini photos showed we weren’t seeing something like surface deposits of frost but a pattern of bright icy cliffs among myriad fractures. This stress pattern may be related to Dione’s orbital evolution and the effect of tidal stresses over time.

Image Credit: NASA