(ORDO NEWS) — New research from the Southwestern Research Institute (SwRI), headquartered in San Antonio, Texas, describes how the unique populations of craters on two of Saturn’s moons could help determine the age of the moons and the conditions under which they formed.
Round craters are very common and can be formed as a result of a wide range of impact conditions. However, elliptical craters are less common and are formed by slow and shallow impacts, which makes them especially useful for determining the age of an object, since the shape and orientation also indicate the trajectory of the shock wave.
Dr. Sierra Ferguson, of SwRI, didn’t initially expect to find a pattern in the directions of the elliptical craters, but she eventually noticed a trend along the equator of Dione, one of Saturn’s minor moons.
There, the elliptical craters were overwhelmingly oriented in an east/west pattern, while closer to the lunar poles, the directions were more erratic.
“Initially, we interpreted this pattern as being representative of two different populations of impactors that created these craters,” she said.
“One group has been responsible for creating elliptical craters at the equator, while another, less concentrated population may be more representative of the normal background population of impactors around Saturn.”
Ferguson also mapped elliptical craters on Tethys, Saturn’s fifth largest moon, and found that this distribution of craters in size and frequency is unusual for solar-orbiting objects, but curiously, it matches estimates of the impactor population, which apparently present on Neptune’s moon, Triton.
Because this population is believed to be planetocentric, or pulled by the ice giant’s massive gravity, Ferguson’s results point to the importance of considering planetocentric impactors when studying the age of objects in the Saturnian system.
The scientist believes that the equatorial craters could have formed from independent disks of debris orbiting each moon, or perhaps from a single disk that affected both moons.
“Using Triton as a guide, Tethys could be billions of years old. This age estimate depends on how much material was available to impact the surface and when it was available,” Ferguson said.
“This study can give us an idea of what the conditions were for the formation of these moons. Was it a completely chaotic system in which materials hit the satellites from all directions, or was it a neat and orderly system.
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