image by Bart Declercq, Haaltert, Belgium

Janssen is a peculiar crater. It is large and made up of multiple craters so we can't easily interpret its shape and history. But with a diameter of about 200 km it is about the size of small impact basins. In fact, Hartmann and Kuiper, in their 1962 basin discovery paper considered that Janssen might be an ancient basin. This piece of a larger mosaic by Bart gives the evidence for the possibility - do you see it? The major diagnostic feature of basins is indicated by their full name: multi-ring impact basins. To the left of Janssen's rim is the arc of a low ridge, is this an outer basin rim? Unfortunately, this ridge is not detected around other sides of Janssen. So is this all that is left of a perhaps partial outer basin ring, or is it not a ring at all, but merely a random ridge? I don't know.

Chuck Wood

Technical Details
Sept 19, 2008, 2h50m UT. C9.25 @ F/20 + DMK31AF @ 30 fps + Astronomik red filter

Related Links
R√ľkl plates 67 & 68
Bart's website


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