Taurus–Littrow

Labeled aerial photo of the Taurus-Littrow valley.

Astronaut Harrison Schmitt is seen next to a large boulder in the Taurus Littrow valley on the Apollo 17 mission in 1972. The South massif is visible to the right.

Taurus-Littrow is a lunar valley located on the Lunar near side at the coordinates 20.0°N 31.0°E / 20.0; 31.0 that served as the landing site for the American Apollo 17 mission, the last manned mission to the Moon to date.

The valley is located on the southeastern edge of Mare Serenitatis along a ring of mountains formed between 3.8 and 3.9 billion years ago when a large object impacted the Moon, forming Mare Serenitatis and pushing rock outward and upward. Taurus-Littrow is located in the Taurus mountain range and south of Littrow crater, features after which the valley received its name. The valley was named by the crew of Apollo 17, and was subsequently adopted by the IAU in 1973.

Geology

The Taurus-Littrow valley is geologically diverse in that during its formation, lavas welled upward from the Moon's interior. As a result of this, rock and soil samples from the area that were collected by astronauts Eugene Cernan and Harrison Schmitt gave insight to the natural history and geologic timeline of the Moon.

Somewhere between 100 and 200 million years after the Serenitatis basin and Taurus-Littrow formed, the lavas that began to seep through the lunar crust began to flood the low-lying areas. These lava flows were often accompanied by fire fountains that blanketed the surrounding area with tiny glass beads. These beads were sometimes colored orange, explaining the orange soil discovered by the Apollo 17 astronauts. Most of these beads, however, where darkly colored, resulting in the dark appearance of the Serenitatis basin from Earth.

The valley itself is elongated along an axis that points toward the center of Mare Serenitatis. Large massifs are located on either side of the valley, called the North and South Massifs, respective to their geographic location in relation to each other. The height of these massifs give the valley a depth greater than that of the Grand Canyon in the United States. Along the South Massif lies Bear Mountain, named after a mountain of the same name near Harrison Schmitt's hometown of Silver City, New Mexico. The sculptured hills and East massif make up the east edge of the valley. To the west, a scarp cuts across the valley floor and rises about 2 kilometers above it. The North and South massifs funnel into the main outlet of the valley into Mare Serenitatis, partially blocked by Family mountain.

Evidence from the Apollo 17 mission shows that the massifs surrounding the valley are composed primarily of feldspar-rich breccia and that basalt underlies the valley floor, a result of the lava flows during the valley's history. Seismic studies suggest that the basalt below the valley floor is about 1400 meters thick. Above the layer of subfloor basalt lies a deposit of unconsolidated material of various compositions ranging from volcanic material to impact-formed regolith. The valley floor's unusually low albedo is a direct result of the volcanic material and glass beads located there. The deeper craters on the valley floor act as 'natural drill holes' and allowed the astronauts to sample the subfloor basalt. These basalt samples are composed primarily of plagioclase, but also contain amounts of clinopyroxene and other minerals.

The unconsolidated regolith layer on the valley floor has a thickness of about 14 meters and contains ejecta from many impacts, most notably the Tycho impact that occurred between 15-20 and 70-95 million years ago. This enabled samples to be retrieved from this impact without having to visit the crater itself. Projectiles from the same impact could have been responsible for the formation of several craters located on the valley floor, creating further opportunities for sampling Tycho ejecta.

Landing site selection

As Apollo 17 was the final lunar mission of the Apollo program, several scientific objectives were identified and several sites previously considered were given consideration again. Taurus-Littrow was one of several potential landing sites considered for Apollo 17 along with Tycho crater, Copernicus crater, Tsiolkovskiy crater on the far side, and others. All but Taurus-Littrow were eventually eliminated for scientific and operational reasons. A landing at Tycho was thought to be too dangerous because of the rough terrain found there, a landing on the far side in Tsiolkovskiy would add the expense of communications satellites necessary to maintain contact between the crew and ground control during surface operations, and a landing in Copernicus was regarded as low priority.

Taurus-Littrow was eventually selected with the objectives of sampling ancient highland material and young volcanic material in the same landing site. The Taurus-Littrow site offered both of these in the form of highland material in the Tycho ejecta sampled and the prospect that some of the craters in the area could be volcanic vents.

External links

Area map