September 25, 2004

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Trough and Pancake



Image Credit: Paolo Lazzarotti

Trough and Pancake

Here is another wonderful image of the Cauchy fault, rilles, domes and crater, to complement the previous low sun view of the western end of this interesting area. This very high resolution image is remarkable for being relatively high sun and yet showing beautifully the low relief domes. Cauchy Tau is clearlyl seen to have slightly irregular topography, like a well behaved version of the Arago domes. Tau has been determined to be 149 m high, based on photometry. The surprise is the flattened look of Cauchy Omega. With its perfectly centered pit, Omega had always before looked to me like a typical hemispherical shield, but now we see it is a pancake. Because it is covered by a high resolution lunar contour map (61D2S), Dick Pike was able to determine that Omega is 6.90 km wide and 116 m high, with a summit pit 1.775 km wide and 231 m deep. Enlarging the image reveals that Omega has a rim nearly all the way around its flat top - in fact, it looks like a miniature version of Wargentin. This tiny rim does not show up in the excellent Apollo 8 oblique view. A lower, smaller, and pitted dome is just visible between Omega and Tau (dashed in mouseover) and a classical hemispherical pitted dome (white circle in mouseover) is north of Tau; both of these domes are also visible on the Apollo 8 image. If you want to wildly over-interpret the image you might say that two more possible low domes or mare swells are are between Tau and a hill in the SW corner of the image. No speculation is required to see the delicate rille at the base of the Cauchy Fault. I first observed this in about 1971 with a 16" Cassegrain telescope - it is rarely observed or imaged. Finally, this remarkable image also shows that the Cauchy Rille appears V-shaped at its ends, but has a broad floor in its middle. Actually, the Lunar Orbiter IV image shows the rille to be flat-floored at the ends too, so the V-shape is not real, but an appearance caused by rille's narrowness. Its a pretty standard little trough.

Chuck Wood

Technical Details:
Sept 3, 2004, Planewton DL-232 (9.5") Newtonian, Lumenera LU075M camera + R+IR filters passing only light at 550-1000 nm); 400/4450 frames @1/30 exposure.

Related Links:
Photometric Studies of Two Domes, A.S. Rifaat, Icarus 7, p. 267-273; 1967.

Yesterday's LPOD: Tranquil Sunshine

Tomorrow's LPOD: Astonishing Megadome

Author & Editor:
Charles A. Wood


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