ESA Science & Technology30-Jun-2005 15:13:22


More Exploration Needed?

In preparation for future human robotic and physical expansion in the Solar System, lunar exploration is continuing, once again with automatic probes, using the far most advanced instrument and computer technologies of today. The successful HITEN (formerly called MUSES-A) Japanese mission was launched in 1990, to perform a sophisticated Earth-Moon circumnavigation, including Earth atmospheric breaking. HITEN was finally directed to impact on 10 April 1993 near Stevinus crater on the southeast part of the lunar side. This hyper-velocity planetary impact could be observed from Earth.

Between February and May 1994, the American Clementine orbiter observed the Moon with visible, and infrared imagers and a laser ranger which mapped practically the entire lunar surface with a 200 m resolution. Its most remarkable discovery was the strong mineralogical and tectonic large-scale inhomogeneity of the Moon. This explains why, even with the Apollo and Luna samples taken from near-side equatorial areas, we do not know the global Moon.

Clementine also discovered the South Pole Aitken basin on the far side, the largest impact basin (2500 km) in the Solar System. Clementine confirmed earlier evidence of permanently shadowed polar craters. A bistatic radar experiment looked at the possible presence of ice in certain polar craters. Clementine's first objective had been to demonstrate new technologies for the United States Strategic Defence Initiative Organisation but lunar and planetary science benefited greatly.

Lunar Prospector followed, launched in January 1998. The low-cost NASA Discovery mission had been designed to provide answers to long-standing questions about the Moon, its resources, structure and origins. Lunar Prospector's 18-month mission reaped very valuable scientific data, mapping thorium and potassium radioactive elements and iron. In March 1998 the Lunar Prospector team confirmed the existence of surface hydrogen, with an enhancement at the lunar poles interpreted as water ice. The spacecraft was then deliberately crashed into the Moon's South Pole, in the hope, a vain one, that this water projected into space would be observed and analysed from Earth.

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