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Tycho (lunar crater)

Tycho is a prominent lunar impact crater located in the southern lunar highlands, named after Tycho Brahe. To the south is Street crater; to the east Pictet, and to the north-northeast is Sasserides crater. The surface around Tycho is replete with craters of various differing radii, many overlapping still older craters. Some of the smaller craters are secondary craters formed from larger chunks of ejecta from Tycho.

Tycho is a (relatively) very young crater, with an estimated age of 108 million years (Ma), based on analysis of samples of the crater rays recovered during the Apollo 17 mission. This age suggests that the impactor may have been a member of the Baptistina family of asteroids, but as the composition of the impactor is unknown this is currently conjecture. However, simulation studies give a 70% probability that the crater was created by a fragment from the same break-up that created asteroid 298 Baptistina.^[1] A larger asteroid from the same family may have been the impactor responsible for creating Chicxulub CrateronEarth 65 Ma ago, and causing the extinction of the dinosaurs.

The crater is sharply defined and free of the wear that affects older craters. The interior has a high albedo that is prominent when the sun is overhead, and the crater is surrounded by a distinctive ray system forming long spokes that reach as long as 1,500 kilometers. Sections of these rays can be observed even when Tycho is only illuminated by earthlight.

The ramparts beyond the rim have a lower albedo than the interior for a distance of over a hundred kilometers, and are free of the ray markings that lie beyond. This darker rim may have been formed from minerals excavated during the impact.

Its inner wall is slumped and terraced, sloping down to a rough but nearly flat floor exhibiting small, knobby domes. The floor displays signs of past volcanism, most likely from rock melt caused by the impact. Detailed photographs of the floor show that it is covered in a criss-crossing array of cracks and small hills. The central peaks rise 1.6 kilometers above the floor, and a lesser peak stands just to the northeast of the primary massif.

Infrared observations of the lunar surface during an eclipse have demonstrated that Tycho cools at a slower rate than other parts of the surface, making the crater a "hot spot". This effect is caused by the difference in materials that cover the crater.

The rim of this crater was chosen as the target of the Surveyor 7 mission. The robotic spacecraft safely touched down north of the crater in January 1968. The craft performed chemical measurements of the surface, finding a composition different from the maria. From this one of the main components of the highlands was theorized to be anorthosite, an aluminium-rich mineral. The crater was also imaged in great detail by the Orbiter V.

From the 1950s through the 1990s, NASA aerodynamicist Dean Chapman and others advanced the "lunar origin" theory of tektites. Chapman used complex orbital computer models and extensive wind tunnel tests to support the theory that the so-called Australasian tektites originated from the Rosse ejecta ray of Tycho. Until the Rosse ray is sampled, a lunar origin for these tektites cannot be ruled out.

This crater was drawn on lunar maps as early as 1645, when Antonius Maria Schyrleus de Rheita depicted the bright ray system.

Satellite craters

By convention these features are identified on Lunar maps by placing the letter on the side of the crater mid-point that is closest to Tycho crater.

Origin

An article published in Astronomy Magazine [1] says that the asteroid that created Tycho probably originated from a large asteroid collision event, believed to have occurred 160 million years ago in the asteroid belt, that resulted in the formation of the asteroid known as 298 Baptistina which is only the largest of a family of asteroids called the Baptistina family. The article says that the asteroid that created Tycho is probably a member of this group along with the asteroid that caused the extinction of the dinosuars at the K-T boundary.

Fictional references

Tycho crater was the location of the Tycho Magnetic Anomaly (TMA-1), and subsequent excavation of an alien monolith, in the seminal science-fiction film and book 2001: A Space OdysseybyArthur C. Clarke. One of the Clavius Base scientists made the prophetic assessment that the monolith "appears to have been deliberately buried."

It also serves as the location of "Tycho City" in Star Trek: First Contact; a lunar metropolis by the 24th century.

InRobert A. Heinlein's book, The Moon Is a Harsh Mistress, Tycho crater is the location of the lunar habitat "Tycho Under".

Gallery

• 
  March 2007 lunar eclipse. The advancing shadow of Earth brings out detail on the lunar surface. The huge ray system emanating from Tycho is shown as the dominant feature on the southern hemisphere.

See also

• Tycho Brahe (crater) (on Mars)

References

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