April 20, 2005

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Almost Classic Crater


Image Credit: Ralf Vandebergh

Almost Classic Crater

Eudoxus is a somewhat unusual impact crater. It has most of the attributes of a complex crater - its is larger than 35 km, has terraced walls, and a relatively flat, partially smooth floor. What it lacks that fresh complex craters have is a significant central peak. Eudoxus has a cluster of small hills, like the nest of a small, untidy bird. Remember this. This image beautifully captures the glacies of Eudoxus. Glacies is a 19th century term for the often abruptly bounded mound that surrounds the crater like a fat tire on a bicycle rim. The glacies is made up of material moved both upward and downward by the crater-forming impact. Impacts act like point source explosions within the lunar crust. The explosion (actually a rarefraction wave) pushes up the crust around the rim of the crater, and this mound is added to by nearly vertically launched ejecta that falls back down around the crater. Studies of terrestrial impact craters suggest that the uplift and fallback each account for about 50% of a crater’s rim height. Finally, do you recognize the rubbly background of Eudoxus? It is small hills and mountains ejected during the formation of the Imbrium basin. I speculate, getting back to the question of Eudoxus’ piddly peaks, that the crater’s formation on the thick layer of Imbrium ejecta debris caused the rebound energy that normally forms central peaks to be dissipated by the rubble. Are there other scrawny central peaks in basin ejecta? Look at nearby Aristoteles.

Chuck Wood

Technical Details:
2004/09/04. 10 inch Newtonian reflector + Philips ToUcam PCVC740k; 1/25 sec. exp.@ 0.19 arcsecond per pixel.

Related Links:
Rukl Plate 13
Lunar Orbiter IV View

Yesterday's LPOD: Before and After

Tomorrow's LPOD: Half a Crater Shadowed

Author & Editor:
Charles A. Wood



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