Deslandres - previously informally called Hellplain - is a fascinating, but often overlooked feature. With a diameter of 234 km (slightly bigger than Clavius at 225 km), Deslandres is one of the larger craters on the nearside. This low Sun image by Italian amateur Cristian Fattinnanza well shows some perplexing features. First, the single arrow with a short tail points to a portion of an arcuate boundary. I can see bits and pieces of other features that suggest an inner ring with a rough diameter of 70 km. Is Deslandres a two ring impact basin, like Compton on the farside? If so, the inner ring is quite small - normally basin inner rings are about 50% of the main ring diameter - or 110 km for Deslandres. Hmm... Also notice the seven arrowheads that mark the edges of a broad rille-like trough. I had never previously noticed this feature, which is about 110 km long and 10 km wide. It is unusual for a rille to be in pure highlands terrain such as this. It is approximately radial to the Imbrium basin but it does not look like a secondary crater chain. Hmm... Finally, observe that many crater floors in this area are rough, containing numerous small impact craters and some small hills. But Regiomontanus, Walter and Stofler (click to see larger image) have smooth floors. I am fascinated by this smoothness and notice it everywhere. Look at Walter W and the circular smooth patch to its west on the floor of Deslandres. And look at Orontius F (on the larger image). All of these smooth patches are considerably younger than other nearby crater floor material. I doubt they are basin ejecta - are they non-mare volcanism?
Hmm... A thought-provoking image, Cristian - thanks!
Related Links:
More about Deslandres (PDF)
Technical Details:
25 cm Newtonian telescope with a Vesta webcam, April 28, 2004.
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