Astronomical Society of Coonabarabran

Apollo 17 and the Taurus-Littrow Dark Mantling

by Harry Roberts

Apollo 17 was the last of the moon landings and unique in several ways. It was the only landing to include a planetary scientist as crew (geologist Harrison Schmitt). The landing was targeted to collect samples of paradoxical dark soils located between very high mountains that needed some fancy flying by pilot Gene Cernan. Evans in the command module would take some incredible images with the vehicle's cameras. The voyage was a huge success, and returned with 110 kg of samples collected during 21 hours of surface exploration, over a three day stay.

Geologically, the interest lay in the almost black soil, the Dark Mantling (DM) that covered part of the Taurus-Littrow area, and was thought to be of recent volcanic origin. A second area of interest was a huge landslide on the north side of the isolated mountain called South Massif (white arrow in Fig 1).

In a recent piece on crater Clerke we touched on the DM region, and on Sept. 18th fair seeing and lighting permitted a sketch of the A17 landing site and the formations that lured the astronauts there.

While the dark mantling is obvious enough, the landslide on the South Massif (SM in Fig 1) is more of a challenge for Earth-based 'scopes, being only 4 km square, and seeing conditions make a big difference. Look for a small spot of white that stands out against the dark background. The astronauts drove the "buggy" to the landslide about six km from the landing site (white cross on Fig 1), and collected samples of the bright material. Wood in "Modern Moon" tells us that when later analysed some of it proved to be 109 million years old, and dated from the Tycho impact, that occurred about 1500 km away! So long-range Tycho ejecta was responsible for the landslide.

On the opposite North Massif the astronauts imaged tracks on the steep slopes where a boulder had slowly slid downhill over millennia. Their photos showed how the slopes slowly degraded, or wasted, as material migrated downwards, leaving them bright and largely free of craters.

When analysed the DM material proved to be ancient and filled with glass "beads' that were interpreted as being "sprayed into the lunar sky from a nearby lava fountain" (Wood, P78). Where the DM material spreads across Mare Serenitatis it forms impressive cliffs as well as the unusual formation I've dubbed the "Fishes Mouth" (FM) just below Clerke.

Apart from the scientific interest of the DM site, the area is particularly beautiful in the eye-piece, with the large isolated massifs looking like jagged ice burgs floating in an inky sea. The A17 photo (Fig 2) shows South Massif in the distance with debris from fresh crater Camelot in the foreground.

Other features seen in Fig 1 are Mons Argaeus that projects into Mare Serenitatis a bit like the Barrenjoey headland. Like the two massifs it is probably about 2 km high. East (right) of the A17 landing site is Mons Vitruvius, also about 2 km high. Crater Fabbroni to the south roughly marks one edge of the DM material, while Clerke marks the northern extent.

Crater Littrow that gives its name to this area is about 20 km north (up, not shown) from the landing site, and the Taurus mountain range is over 100 km north. Littrow was Johann von L., 1781 - 1840, an Austrian astronomer. Giovanni Fabbroni, 1752 - 1822 was an Italian chemist, and Agnes Clerke has been covered in an earlier piece on the area.

Take a closer look and see if you can detect the landslide that drew the astronauts to this complex region.

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