LROC: Pytheas

A lovely combination of layered mare basalt, granular flow, and talus. The top of the image is down-slope. LROC Narrow Angle Camera (NAC) observation M170694505L, orbit 10289, September 15, 2011; image field of view is 735 meters, pixel scale of 0.49 meters per pixel from 45.53 kilometers. See the much larger full sized LROC Featured Image HERE [NASA/GSFC/Arizona State University].

Sarah Braden
LROC News System

Inside the southern rim of the crater Pytheas (20.55°N, 20.6°W) is a great combination of layered mare basalt, granular flow, and talus. In the bottom left hand corner of the Featured Image you can see the details of erosion where granular material fell away from the rest of the surface near the rim. The high reflectance (bright) tendril of material flowed in a narrow band over the layers of lower reflectance (darker) mare basalt, then, after clearing the basalt layers, finally spread into a wide cone of talus. Talus cones are common on the Earth, with some stunning examples that may rival the Moon's beauty. On the Moon, talus deposits are created entirely by gravity, but on the Earth wind and water play a role in their formation.

A somewhat 'twisted' view of the larger slope context of the granular flows in the Featured Image from the LROC NAC frame. The apparent floor contact is, in fact, far from the crater's lowest elevations, on the opposite side of Pytheas [NASA/GSFC/Arizona State University].

A particularly detailed LROC Wide Angle Camera (WAC) monochrome (604 nm) 66 meter per pixel resolution image of Pytheas and Pytheas D directly to its north, the topography of its interior, and exterior ejecta blanket as well as albedo chevron, stitched from three sequential orbital viewing observations under an average 54.7° incidence angle from 46.8 kilometers, November 18 and 19, 2010 [NASA/GSFC/Arizona State University].

The same LROC WAC 604 nm mosaic at 50 percent (132 meter) of its original resolution offers a fuller view of the Pytheas chevron and other rays, apparently "downwind" from the Copernicus impact. The small crater to the west of Pytheas is Pytheas A. The inset shows elevation range of the Pytheas environs from LROC's versatile QuickMap [NASA/GSFC/Arizona State University].

Pytheas and the south-central Imbrium basin clearly had their topography and appearance affected by the relatively recent arrival of the Copernicus progenitor, 800 million years ago. LROC WAC 100m Global Mosaic overlaid upon LOLA digital elevation model (v.2) in the NASA ILIADS application [NASA/GSFC/Arizona State University].

Pytheas was a Greek geographer and explorer (circa 325 BC) from a Greek colony in what is now Marseilles, France. He is especially important to lunar geology since his report on Earth's ocean tides was probably the first to associate the tides with the phases of the Moon.

Explore the entire NAC frame, HERE.

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