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Planetary scientists are using the Hubble Space Telescope to scout out sites for potential human bases on the Moon.
Previous missions have observed the Moon at a range of wavelengths. But none have boasted Hubble's sharp resolution at ultraviolet wavelengths - it can identify spectral features just 50 metres across over swathes of lunar terrain.
"We're trying to ascertain the potential of ultraviolet spectra for indicating lunar resources," says Bruce Hapke, a planetary scientist at the University of Pittsburgh in Pennsylvania, US. He is one of a team of six researchers led by NASA's chief scientist, Jim Garvin, using Hubble to view the Moon.
In particular, the team hopes to be able to identify a mineral called ilmenite - or iron titanium oxide - which has previously been found in lunar soil samples. "It has properties which would be useful in constructing a lunar base," Hapke told .
Ground-truth calibration
It contains oxygen, which could be extracted for breathing, as well as hydrogen and helium absorbed from the solar wind. Heating the mineral would release the gases, which could then be used as a power source for the base, says Hapke. Iron in the mineral might eventually be used to produce construction materials, such as steel, for lunar buildings.
Ilmenite was found in different concentrations in the several areas visited by the Apollo astronauts more than three decades ago. Hubble observed two of these sites - where Apollo 15 and Apollo 17 astronauts touched down in 1971 and 1972, respectively - as part of an observing run that finished on Sunday.
"We're looking at those two sites because we know what's there," says Hapke, who was a principal investigator for the Apollo lunar sample analysis. "This is a ground-truth calibration" for ultraviolet studies of the Moon, he says.
Magma ocean
Hubble also looked at a third site - a 42 kilometre-wide crater called Aristarchus, near the Moon's equator. The crater lies near the edge of a plateau that rises about 2 km above the vast lava plains that surround it.
Previous observations suggest the impact that created it threw up material from both the plateau and the plains, which were once covered by an ocean of magma. That ejecta is more likely to contain useful minerals. The Clementine spacecraft examined the region in visible and near-infrared wavelengths and Hapke says: "From the measurements made at longer wavelengths, it looks like there are a number of places where minerals of interest are exposed."
He adds that the time for the Hubble observations would probably not have been allocated were it not for US president George W Bush's "Vision for Space Exploration", which calls for returning people to the Moon by about 2018.
NASA expects to release the results of the Hubble observations of the Moon by early October 2005.
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