Tiny Peaks
images from Clementine at USGS Map-A-Planet
My first scientific paper was on central peaks of lunar craters, and I haven’t lost my fascination with them yet. Studies of terrestrial impact craters demonstrate that central peaks are rebounds of deep target rocks. Rocks from a depth beneath the surface of roughly 1/10th a crater’s diameter are exposed in peaks. Thus, the central mountains on the floor of 93 km wide Copernicus are thought to come from about 6-10 km below the surface. When I originally studied peaks I used photographs from Kuiper’s 1960 Photographic Lunar Atlas. I discovered that peaks are rare in craters smaller than 10-15 km in diameter and become progressively more common in larger craters. I repeated this study in 1978 using Lunar Orbiter images and found that nearly all fresh craters larger than 35 km have central peaks but fewer than 4% of craters smaller than 5 km have peaks. The newer Clementine data with the high Sun imaging of much of the Moon suggests that central peaks may be more common in small craters than I thought in 1968 and in 1978. The 15 km wide farside crater Glauber has a perfect bright dot of a peak on its flat floor. So does the like-sized Dunthorne, and the floor of 17 km wide Maury is crowded with five rounded hills. At a crater diameter of 15 km, peaks are not completely rare but are less uncommon than I thought. The USGS Map-A-Planet site has been down the last couple of days so I can’t check Clementine, but it will be worthwhile to look for peaks in smaller craters.
Chuck Wood
Related Links:
My original article on central peaks was in the Communications of the Lunar and Planetary Lab and is not on line.
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Chuck: yesterday I have reported the problem with the MAP-A-PLANET server to the webmaster, but it is still unavailable.
Comment by Paolo Amoroso — August 22, 2007 @ 3:43 am
Paolo -I reported it too - they have a server failure and hope to get it back up soon. I’ve realized that I use it nearly every day.
Chuck
Comment by chuckwood — August 22, 2007 @ 6:42 am
Paolo, there’s always the book THE CLEMENTINE ATLAS OF THE MOON by Ben Bussey and Paul Spudis!
And… this atlas shows the grid of the 144 LAC-charts!
I like this atlas very much.
Thanks B.Bussey and P.Spudis!
Danny Caes.
Public Observatory of Ghent - Belgium.
Comment by caligula — August 22, 2007 @ 6:45 am
Thanks Danny, but I can’t submit chunks of the Clementine Atlas to the LPOD Photo Gallery
Comment by Paolo Amoroso — August 22, 2007 @ 9:10 am
But then what’s so different between two craters of the same size that one forms a peak and the other one not?
Hans
(yet another Belgian)
Comment by hansvi — August 22, 2007 @ 12:34 pm
Peaks are produced by the rebound of target rocks that have been compressed by the energy of impact. During the impact and rebound the rock acts almost like jello and the central part that has been depressed most springs up to make the peak. It isn’t clear to me if there are tiny peaks in small craters that we don’t see with our normal images. Or if there is a threshold energy (corresponding to a certain crater diameter) where the peaks suddenly form. I think in the 5-15 km diamter range we are near the energy level when peaks form so that small differences in local characteristics may promote or retarn peak formation. And there is the complication of rocks and their weaknesses and strengths that influence what happens too.
Comment by chuckwood — August 22, 2007 @ 12:46 pm