What did Clementine and Lunar Prospector Tell Us About the Moon?
Lunar far side of the Moon, captured by Clementine.
Lunar near side of the Moon, captured by Clementine.
Generalized mineral map of the Moon; red is relative anorthite abundance, green represents olivine abundance, and blue shows total pyroxene abundance. The map is centered on the far side of the Moon highlighting the large-scale compositional unit associated with the South Pole-Aitken basic (SPA). Note the lack of olivine (green) in SPA, hinting that the SPA impact event did not excavate mantle material. Note also the large region of olivine basalts (green) in western Oceanus Procellarum (15°N, 55°W). The black regions indicate no compositional estimates avaiable.
Clementine: A New Beginning.
The Clementine spacecraft (right) orbited the Moon and collected science data for 10 weeks in the Spring of 1994. During this time it collected global multi spectral images and near global altimetry. Select areas of the Moon were imaged at 25 m/pixel in visible light and 60 m/pixel in thermal wavelengths. From these data a new paradigm for the evolution of the lunar crust emerged. The Moon is no longer viewed as a two-terrane planet, the Apollo samples were found not to represent the lunar crust as a whole, and the complexity of lunar crustal stratigraphy was further revealed. More than ten years later the Clementine datasets continue to significantly advance lunar science and will continue to do so as new measurements are returned from planned missions such as Chandrayaan, Kayuga, and Lunar Reconnaissance Orbiter.
Lunar Prospector
NASA's Lunar Prospector Mission orbited the Moon from 1998-1999 and provided important new insights into the origin and evolution of the lunar crust. It carried no cameras but rather carried an array of instruments to produce the first global maps of the Moon's gravity, magnetic field, and surface composition. Two instruments in particular produced vital results: the Neutron Spectrometer, which was designed to detect the water hypothesized to exist in some places on the Moon's surface [see below], and the Gamma-Ray Spectrometer (LP-GRS), which directly measured the global distribution of key elements such as iron, potassium, and thorium on the Moon's surface for the first time. The LP-GRS was particularly sensitive to thorium, which is naturally radioactive. This gave lunar scientists their first look at the global distribution of an important thorium-rich lunar material known as KREEP (for Potassium, Rare Earth Elements, and Phosphorous).
Before the Lunar Prospector mission, it was assumed that KREEP materials were a component in a nearly global layer beneath the lunar crust, but the Lunar Prospector results showed that the KREEP materials were concentrated on the lunar nearside, a fact which could be related to the distribution and longevity of lunar mare volcanism.
Before the Lunar Prospector mission, it was assumed that KREEP materials were a component in a nearly global layer beneath the lunar crust, but the Lunar Prospector results showed that the KREEP materials were concentrated on the lunar nearside, a fact which could be related to the distribution and longevity of lunar mare volcanism.
Lunar South Pole.
Lunar Hydrogen Abundance.
Lunar Polar Ice?
Although the Moon rocks brought back to Earth by the Apollo astronauts contain no water or hydrous minerals, there are permanently shadowed regions near the lunar north and south poles where sunlight never penetrates. These shadowed regions could act as cold traps for ice deposited by comets impacting the lunar surface. Lunar Prospector's Neutron Spectrometer instrument detected high levels of hydrogen (presumably, the H in H2O) at both lunar poles (shown in the purple and blue areas in the maps below). This has been interpreted to reflect the possible presence of water ice in these craters. Water can be used for life support, agriculture, and propellant, and ice would be a vital resource for future lunar settlers. Understanding how much water, if any, exists at the lunar poles is therefore an important goal of future lunar exploration.
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