November 17, 2014
Ejecta Deposits
image by Jocelyn Serot, France
This is the splash zone for the Imbrium Basin impact. Not a literal splash of some pre-existing liquid, but a zone where solid and in some places fluidized rocky material, smashed and excavated during the impact, was deposited, some ballistically and some perhaps traveling across the surface as a hyper-hurricane surge. In looking at this area you can try to understand the nature of each deposit. First, there are some later, post-impact events to remove in your minds eye to avoid confusion. Philolaus, Fontenelle and other relatively fresh craters with continuous rims - especially all the small ones that cast shadows - are clearly later events: use your mind's version of PhotoShop to scrape them away. The other type of obvious post-Imbrium deposit is the patch of Mare Frigoris lavas at the bottom of Jocelyn's image. The fact that lava is there says that the area was already a depression, perhaps the north shore of Frigoris is part of the Imbrium Basin rim. The large, pre-existing craters nearest to Frigoris (Birmingham and the circular remnants between there and Philolaus) have heavily damaged rims and floors filled with rubbly debris - they were closer to ground zero and received the most battering. The darkish smooth material a third of the way from Fontenelle to Philolaus is probably a leak of mare lava, judging by its yellow color on the Clementine color ratio mosaic. The fact that most of the remnant craters are large suggests that the basin ejecta is thick enough, perhaps 2-3 km, to completely bury and hide smaller craters. At the distance of Pascal and Brianchon (upper left), pre-Imbrium craters retain their rims and depressed floors, but are shallowed by ejecta. Really, there is no place in this image that you'd want to be 3.8 b.y. ago when the Imbrium-forming asteroid hit - it probably wasn't safe on Earth, either.
Chuck Wood
Technical Details
16/09/2104, 5h51 CET. Celestron C11 @ F/D=20 (Barlow 2x), R filter, Basler acA1300-30-gm camera; processing Autostakkert2 + Registax 6
http://www.astrosurf.com/legalet/Bazar/Philolaus_C11_B16__2014-09-16_T_05-51-00-0984_R_AS_f300_g4_ap1649.png
Related Links
21st Century Atlas charts 19 & L8.
Yesterday's LPOD: An Image To End All Images (Almost)
Tomorrow's LPOD: Inconstant Star
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