According to a new SwRI research, the distinct populations of craters on two of Saturn's moons might help determine the satellites' age and creation circumstances. SwRI postdoctoral researcher Dr. Sierra Ferguson surveyed elliptical craters on Saturn's moons Tethys and Dione using data from NASA's Cassini mission for this study, which was co-authored by SwRI Principal Scientist Dr. Alyssa Rhoden, Lead Scientist Dr. Michelle Kirchoff, and Lead Analyst Dr. Julien Salmon.
"Our research intends to provide an answer to the more general issue of how ancient these moons are. To answer this question, my colleagues and I measured the size, orientation, and placement of elliptical craters on the surfaces of these moons "Ferguson remarked.
Circular craters are quite common and can result from a variety of impacts. Elliptical craters, on the other hand, are more common and originate from slow, shallow impacts, making them particularly valuable in estimating an object's age because their shape and orientation also reveal the impactor's track.
"We can obtain a notion of what the impactors that generated these craters looked like in a dynamical sense and from which direction they may have impacted the surface by measuring the way these craters point," she added.
Ferguson didn't expect to uncover a pattern among the paths of the elliptical craters at first, but she did see one near Dione's equator, one of Saturn's minor moons. There, elliptical craters were primarily directed east/west, whereas orientations near the moon's poles were more random."At first, we thought this pattern represented two separate impactor populations causing these craters," she explained. "One group was responsible for the elliptical craters around the equator, while another, less concentrated population might be more reflective of Saturn's usual background population of impactors."
Ferguson also surveyed elliptical craters on Tethys, Saturn's fifth biggest moon, and discovered that a comparable size-frequency distribution of craters is rare for objects circling the Sun, but oddly fits predictions for the impactor population on Neptune's moon Triton. Ferguson's findings highlight the relevance of considering planetocentric impactors for determining the age of objects in the Saturnian system because that population is assumed to be planetocentric, or attracted in by the ice giant's tremendous gravity.
"Seeing these patterns was quite amazing," she remarked.
The equatorial craters, according to Ferguson, might have developed from separate disks of debris around each moon, or from a single disk that damaged both moons."Tethys might be billions of years old if we use Triton as a reference. This age estimate is based on the amount of material available and when it was accessible for striking the surface "Ferguson remarked. "Of course, we'll need more data to be certain, but this study tells us a lot. It can provide insight into the conditions under which these moons formed. Was this a system that was utterly chaotic, with things flying all over the place, or was it a well-organized system?"
Ferguson expects to be able to compare her Saturnian moon data to that of Uranus, another ice giant, in the future. While present evidence is unconvincing, a journey to Uranus and its moons is one of the flagship projects advocated by the Planetary Science Decadal Survey, which was published in April.
"This is the first step toward a fresh viewpoint on these moons' cratering history, genesis, and development," Ferguson said.
