Notable Surface Features

Prominent and noteworthy features of the lunar surface range from prominent craters such as Copernicus and Tycho to sites important in humanity's brave history of lunar exploration such as Taurus-Littrow and Hadley Rille.

Copernicus is one of the most prominent craters on the Moon. It constitutes a classic example of a relatively young, well-preserved lunar impact crater. Located at 10° N, 20° W, near the southern rim of the Imbrium Basin (Mare Imbrium) impact structure, Copernicus measures 93 km (58 miles) in diameter and is a source of radial bright rays, light-coloured streaks on the lunar surface formed of material ejected by the impact. Photographs of the crater taken from spacecraft above the Moon show terraced slumps on the crater walls that resemble giant stairs leading to the floor, 3.8 km (2.4 miles) below the rim crest. Peaked mountains rise from the centre of the crater to a height of 800 metres (2,600 feet); they probably were formed as a result of a rebound of deep-seated rocks at the site of impact. Lunar scientists estimated that Copernicus was created less than one billion years ago.

The Fra Mauro crater appears to be heavily eroded. It was named for a 15th-century Italian monk and mapmaker. About 80 km (50 miles) in diameter, Fra Mauro lies at about 6° S, 17° W, in the Nubium Basin (Mare Nubium) impact structure. The name is also applied to the extensive surrounding region, called the Fra Mauro Formation, which lunar scientists interpret to be material ejected from the impact that formed the giant Imbrium Basin (Mare Imbrium) to the north—the largest impact basin (mare) on the Moon's near side.

A broad, shallow valley within the formation about 50 km (30 miles) north of Fra Mauro crater served as the site of the Apollo 14 manned lunar landing in February 1971. On two separate Moon walks, Apollo astronauts Alan Shepard and Edgar Mitchell collected samples of what was believed to be ejected rock; in later radiometric analysis on Earth, this material was found to have been thermally shocked about 3.9 billion years ago, presumably by the cataclysmic event that created Imbrium.

Hadley Rille is a typical sinuous rille. The feature was a primary site of exploration for the Apollo 15 lunar-landing mission. Named for the 18th-century English inventor John Hadley, the rille is located at approximately 26° N, 3° E, at the southeastern edge of the great lava-filled Imbrium Basin (Mare Imbrium) impact feature. The steep-walled valley, about 1.5 km (0.9 mile) wide and 400 metres (1,300 feet) deep, winds for more than 100 km (60 miles) across the plains of Palus Putredinis along the foot of the Apennine mountain range, a part of the Imbrium Basin's upthrown ramparts.

The rille is easily visible with a telescope from Earth under the right lighting conditions (low-angle morning or evening illumination at the site) and with good seeing (a state of low turbulence in Earth's atmosphere that allows sharp telescopic images). In July 1971 Apollo 15 astronauts drove their rover to the brink of the curving canyon and photographed possible layering in its eroded walls suggestive of stratified lava beds. Because all lunar features are covered by impact debris and no mission has yet visited the interior subsurface of a rille, the true origin of Hadley Rille and other sinuous rilles remains to be elucidated.

The Taurus-Littrow Valley region on the Moon was selected as the landing site of the Apollo 17 manned lunar mission. Located at 22° N, 31° E, it is named for the surrounding Taurus Mountains, a part of the ramparts of the Serenitatis Basin (Mare Serenitatis) impact structure, and for the nearby 30-km- (19-mile-) diameter crater Littrow.

The site was chosen because it had geologic features promising a varied collection of images, samples, and other data from both ancient highland and younger volcanic areas. In December 1972, after descending to the Moon, Apollo astronaut Eugene Cernan and geologist-astronaut Harrison Schmitt deployed their lunar rover and traveled for a total of 36 km (22 miles) on three separate excursions around the valley, retrieving samples that had come downslope from the nearby highlands and collecting specimens of the variegated, titanium-rich mare basalt rocks and soils filling the valley. They also collected samples of orange and black glass indicative of ancient volcanic "fire fountains" (eruptive gouts of lava) on the Moon.

Sample analyses conducted on Earth interpreted the highland rocks as parts of the material excavated by the enormous impact that created the Serenitatis Basin. Some rocks from the Taurus-Littrow site, which is crossed by one of the rays of material ejected from the impact that formed the comparatively young crater Tycho, suggested an age for the crater of about 100 million years. The complex geologic history of the Taurus-Littrow region makes it a prime target for future scientific landing and roving missions on the Moon.

Tycho is the most conspicuous impact crater on the Moon. It lies at the centre of the most extensive system of bright rays on the near side. The rays, which are light-coloured streaks formed of material

Apollo 17 geologist-astronaut Harrison Schmitt at the foot of a huge split boulder, December 13,1972, during the mission's third extravehicular exploration of the Taurus-Littrow Valley landing site. NASA

ejected from the impact, dominate the southern highlands and extend for more than 2,600 km (1,600 miles) across the Moon's surface.

Tycho, located at 43° S, 11° W, in the highlands south of the Nubium Basin (Mare Nubium) impact structure, measures 85 km (53 miles) in diameter and about 4 km (2.5 miles) deep. Laboratory analysis of samples returned in 1972 by

Apollo 17, whose landing site was crossed by one of Tycho's rays, suggests that the crater was formed about 100 million years ago. Because of its relatively young age, the crater retains hummocky rim deposits, terraced walls, and seemingly fresh pools of dark flowlike materials. Multispectral images from the lunar-orbiting robotic Clementine spacecraft in 1994 show that the composition of

Tycho's central peak differs from that of other parts of the crater, consistent with the idea that such features of craters result from a rebound of rocks originating at greater depths in the crust under the centre of the impact.

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