Far side of the Moon
[13] The two hemispheres of the Moon have dramatically different appearances, with the near side covered in multiple, large maria (Latin for 'seas', since the earliest astronomers incorrectly thought that these plains were seas of lunar water).
One commonly accepted explanation for this difference is related to a higher concentration of heat-producing elements on the near-side hemisphere, as has been demonstrated by geochemical maps obtained from the Lunar Prospector gamma-ray spectrometer.
[15] In this model, the impact led to an accretionary pile rather than a crater, contributing a hemispheric layer of extent and thickness that may be consistent with the dimensions of the far side highlands.
"[16] Newer research suggests that heat from Earth at the time when the Moon was formed is the reason the near side has fewer impact craters.
The lunar crust consists primarily of plagioclases formed when aluminium and calcium condensed and combined with silicates in the mantle.
The Moon's highest and lowest points, along with its tallest mountains measured from base to peak, are all located on the far side.
Librations periodically allowed limited glimpses of features near the lunar limb on the far side, but only up to 59% of the total surface of the Moon.
[19] These features were seen from a low angle, hindering useful observation (it proved difficult to distinguish a crater from a mountain range).
[20] On 7 October 1959, the Soviet probe Luna 3 took the first photographs of the lunar far side, eighteen of them resolvable,[21][20] covering one-third of the surface invisible from the Earth.
[25] In 1961, the first globe (1:13600000 scale)[26] containing lunar features invisible from the Earth was released in the USSR, based on images from Luna 3.
[27] On 20 July 1965, another Soviet probe, Zond 3, transmitted 25 pictures of very good quality of the lunar far side,[28] with much better resolution than those from Luna 3.
In particular, they revealed chains of craters, hundreds of kilometers in length,[22] but, unexpectedly, no mare plains like those visible from Earth with the naked eye.
This caused some controversy, though the Soviet Academy of Sciences selected many non-Soviet names, including Jules Verne, Marie Curie and Thomas Edison.
[34] The first truly comprehensive and detailed mapping survey of the far side was undertaken by the American uncrewed Lunar Orbiter program launched by NASA from 1966 to 1967.
Spacecraft passing behind the Moon were out of direct radio communication with the Earth, and had to wait until the orbit allowed transmission.
[35] It has since been used for communications between the Chang'e 4 lander and Yutu 2 rover that have successfully landed in early 2019 on the lunar far side and ground stations on the Earth.
In February 2020, Chinese astronomers reported, for the first time, a high-resolution image of a lunar ejecta sequence, as well as direct analysis of its internal architecture.
[39][40] CNSA launched Chang'e 6 on 3 May 2024, which conducted the first lunar sample return from Apollo Basin on the far side of the Moon.
Small, bowl-shaped craters provide a natural formation for a stationary telescope similar to Arecibo in Puerto Rico.
One of the NASA missions to the Moon under study would send a sample-return lander to the South Pole–Aitken basin, the location of a major impact event that created a formation nearly 2,400 km (1,500 mi) across.
The force of this impact has created a deep penetration into the lunar surface, and a sample returned from this site could be analyzed for information concerning the interior of the Moon.
