April 6, 2013

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Streamlined Islands

image by Mike Wirths, Baja California, Mexico

Like most excellent images this one has all sorts of distractions, rilles, little ejecta-covered domes, kipukas (google it), and the odd, polygonally-shaped craters Kepler, Encke and Kunowsky. And of course, rubbly deposits of Imbrium ejecta are pretty much where ever lava isn't. But lets focus in on the hills due west (left) of Kepler. We've discussed before how the 750 m linear ridge (Kepler Kappa) west of Kepler appears to have blocked ejecta, which is both to the north and south of the ridge. But it is clear that Kappa, the three short linear hills to its north, the slightly bigger hill to their west and then the more massive hill, Kepler Pi, casting a shadow towards the terminator, are all that is left of the rim of a 55 km wide impact crater. What seems astonishing is that most of the rim of the crater is completely missing, but somehow isolated peaks rising 750 m (Kappa) and 550 m (Pi) above the mare are preserved. All of these peaks are elongated radial to the center of the Imbrium Basin, and the parts of the crater rim that were perpendicular to Imbrium are gone. So this is just like the area between Hyginus and Serenitatis, where many crater walls are reduced to Imbrium radial ridges. Presumably a mega-hurricane of Imbrium ejecta came roiling across the surface, smashing away topography blocking its path, and leaving only streamlined islands pointing towards the source of destruction. I wonder where the eroded away rim rocks were deposited, or were they leaked along the surface as the ejecta plume slowed down. You really wouldn't want to be anywhere near here 3.8 billion years ago.

Chuck Wood

Technical Details
Starmaster 18" (Zambuto optics), ASI120MM camera, 2.5X's powermate barlow, R/IR filter, Firecapture, and PS CS, topaz infocus

Related Links
Rükl plate 30
21st Century Atlas chart 22.
Mike's Baja Skies B&B

Yesterday's LPOD: Don't Give Me Any of Your Lip

Tomorrow's LPOD: Death Moonrise


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