A new study shows how unique populations of craters on two of Saturn's moons could help show how old the satellites are. Dr. Sierra Ferguson used data from NASA's Cassini mission to survey elliptical craters on Tethys and Dione.
We want to answer the bigger question of how old these moons are. Ferguson and his colleagues mapped elliptical craters on the moon's surface to determine their size, direction and location.
Circular craters can be formed from many different impact conditions. elliptical craters are useful in determining an object's age because they are rare and form from slow and shallow impacts.
She said that by measuring the direction these craters point, we can get an idea of what the impactors that made these craters look like.
Ferguson was not expecting to find a pattern among the elliptical craters, but she eventually noticed a trend along the equator of Dione. The elliptical craters were oriented in an east/west pattern, while the directions were more random near the moon's poles.
She thought the pattern was representative of two different impactor populations. One group was responsible for the creation of the elliptical craters at the equator, while another group may be more representative of the regular background population of impactors.
The elliptical craters on Tethys are similar to the impactor population on Neptune's moon, but curiously matches estimates for the impactor population that appears to be present on Neptune's moon. Ferguson's results show the importance of considering impactors when looking at the age of objects in the system.
She said it was amazing to see the patterns.
The equatorial craters could have been formed from independent disks of debris around each moon, or a single disk that affected both moons.
The Tethys could be billions of years old. The age estimate is dependent on how much material was available to impact the surface. We will need more data, but this research shows us a lot. It can show us what the formation conditions were like. There was a chaotic system with materials hitting the satellites every which way, or there was a neat and orderly system.
Ferguson wants to compare her data from the moons of the ice giant with that of the other one. One of the flagship missions recommended by the Planetary Science Decadal Survey is to go to Uranus and its moons.
Ferguson said that this was the first step towards a new perspective on the cratering history of the moons.
The study is in a journal.
More information: Sierra N. Ferguson et al, A unique Saturnian impactor population from elliptical craters, Earth and Planetary Science Letters (2022). DOI: 10.1016/j.epsl.2022.117652 Journal information: Earth and Planetary Science Letters
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