Free Astronomy Magazine January-February 2021

38 JANUARY-FEBRUARY 2021 ASTRO PUBLISHING A n annotated VIMS RGB colour image showing the nine dune and plain im- pact craters on Titan from the recent study of crater composition and evo- lution. The yellow sections indicate the crater floors and the red sections are the ejecta blankets. Menrva is the largest crater, and Selk will be visited by NASA’s Dragonfly mission in 2034. [Solomonidou et al. (2020); background map: Le Mouélic et al. (2019)] while higher emissivity indicates an organic-rich layer. The VIMS data can be used to look at the thin ‘veil’ that covers the surface. Using VIMS to study the surface of Titan requires an under- standing of the methane absorption and haze in the at- mosphere, which was provided by the Huygens data and the use of a radia- tive transfer code. The team then used a new mixing model to study the chemi- cal composition of the crater floors and ejecta blankets (i.e. material thrown out of the crater area during the impact). The results showed that the dune craters and the plain craters have two dif- ferent types of composition. The plain craters have a mix of organics and are enriched with water ice, whereas the dune craters have mainly organic material and no wa- ter ice. Both types of craters have S inlap is thought to be the youngest crater on Titan. The RADAR image of Sinlap is shown in (a), the VIMS image in (b), and the two are combined in (c) with yellow areas selecting the crater floor and white areas the ejecta blanket. The data from these areas were used in a recent study of crater composition and evolution on Titan. [Solomonidou et al. (2020)]