Radar data show that Enceladus geysers throw out water that turns into snow. Not only does the snow fall back on the surface of Enceladus, it also makes its way to its neighboring moons, Mimas and Tethys, making them more reflective. Researchers call this a "snow cannon".
The Cassini spacecraft carries a powerful radar designed to penetrate the thick, opaque atmosphere of Titan, Saturn's largest moon. But it was also pointed to other moons, including Mimas, Enceladus, and Tethys, in an attempt to measure their albedo and characterize their surfaces.
New results from a team of scientists working with Cassini's radar data say that some of the data has previously been misinterpreted and that some of Saturn's moons are much brighter than thought. These results, and a model developed to explain them, show that Enceladus is the source of the snow that falls on two of Saturn's other moons, increasing their reflective power.
These radar measurements were designed to measure the albedo of many moons on Saturn. Enceladus had the highest albedo and the hazy Titan had the lowest. Two of the other moons, Mimas and Tethys, also had high albedo. In terms of orbits, Mimas and Tethys are hiding Enceladus. So the three brightest moons were close to each other.
The results are in a poster presented at the EPSC-DPS 2019 Joint Meeting in Geneva by Dr. Alice Le Gall. The high albedo of the three moons Enceladus, Mimas and Tethys points to clear and pure water ice in the subsurface of the moons, as well as to the presence of "scattering structures" that are "particularly effective in returning scattering waves" . according to the poster.
Dr. Le Gall, of LATMOS-UVSQ, Paris, explained: “The ultra-bright radar signals we observe require a snow cover of at least a few tens of centimeters thick. However, the composition cannot explain the extremely bright levels recorded. Radar waves can penetrate transparent ice up to several meters and therefore have more potential to bounce off buried structures. The surfaces of the inner moons of Saturn should contain high-efficiency reflectors that preferably deflect the scattering radar waves to their source. "
But researchers still do not know what these structures are. Image Credit: NASA / JPL-Caltech / Space Science Institute. Enceladus has various surface characteristics and sub-roof characteristics related to the effects and thermal stress on its icy surface. There are peaks, ice blocks and areas with dense cracks. So far, there is no evidence that these characteristics can cause back scattering.
Ice forms of the earth can form other more exotic types of structures that could be responsible for reflectivity. Penitentes are thin, elongated blades of snow or ice that are closely aligned together and point to the sun. Suncups are open depressions on a snowy surface that are also highly reflective. But they need a lot of solar energy to form, and it's not clear if they get enough.
p. Le Gall and his colleagues have developed models that will allow them to test whether specific characteristics contribute to the high albedo or whether more random events cause it. Right fractures on the icy surfaces of these inner moons may cause it.