RoI - Anaxagoras Crater

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Anaxagoras Crater

(Tier 1 Region of Interest for Constellation Program)

Official NASA Overview

source: NASA Cx-LROC Tier 1 Targets (PDF); see expanded details below

Scientific Rationale

Crater central peak

The central peak material of Anaxagoras is believed to consist of pure anorthosite, which, by definition, is a coarse-grained, mafic (MAgnesium + Iron FerrIC) igneous plutonic rock -- one that has formed at considerable depth within a planet or moon -- approaching 98% volume in plagioclase (a feldspar mineral). The anorthosite presence is believed to be a signature of differentiaton processes (its low density caused it to float to the top forming a thin crust) in a magma ocean that once encompassed the early-forming Moon. Recent reflectance spectral data obtained by the Japanese Kaguya/Selene spacecraft which launched three years ago (and subsequently crashed onto the lunar surface in June 2009), points to the possibility of a global layer of pure anorthositic rocks in the upper crust of the Moon. Signatures of the anorthosite deposits, composed of nearly 100% volume plagioclase, particularly showed up in areas of crater central peaks, walls, ejecta and basin rings, and is suggested as being ubiquitously present within the depth range from 3 km to at least 30 km in a global perspective. Whether this latter finding is the case or that the pure anorthorsitic signatures are due to discrete intusive bodies is still uncertain, however, further analyses around such regions are certain to provide a constraint on models of lunar magma ocean formation and formation of the Moon. - JohnMoore2

Impact process

Some of the central peak material of Anaxagoras overlies the south-western sector of its terraced crater walls. The impact processes involved caused material (anothorsite in this case) at depth in rebounding upwards to form the central peak; suggesting that its resultant asymmetric appearance may be due to collapse sideways of the material. Other influential mechanisms, like impactor direction or underlying rock material, may have played a role in the central peak's appearance, so Anaxagoras provides a unique region in which to better understand peak formation as a whole. - JohnMoore2


Left: Lunar Orbiter 4 LO-4140-H2 image from LPI.
Middle: Geological sketch map of Anaxagoras -- adapted from J. B. Murray's 1979 paper "Oscillating Peak Model of Basin and Crater Formation", page 296 (NB. Sketch has been orientated to suit side-images that have North up and West left).
Right: Geologic Map image (1978) from LPI. Click image for larger view

anaxagoras-small2.jpgClick image for larger view

Additional Information

LROC Links

  • Featured Image -- Exposed Fractured Bedrock in the Central Peak of the Anaxagoras Crater

LPOD Articles

Blue Dots, White Rocks, Stratigraphy of Brightness, North Polar Rays, Was Anaxagoras an Oblique Impact, Page One of a New Book, Color Me Anorthosite.

General Bibliography