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Comets as water carriers of the moon

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January 16, 2011, 12:42 pm

Water that can be detected on the moon may have reached the earth's satellite when a comet struck.

Moon surface in the infrared - zones of strong infrared absorption in blue
(Image: ISRO / NASA / JPL Caltech / USGS / Brown Univ.)
The water on the moon came on him in large quantities in his childhood when comets bombarded its surface. This is the result of a study that became known in early January 2011.

For decades, many scientists assumed that the moon was extremely dry because there was no trace of life and no evidence of an atmosphere. Traces of water in lunar rocks examined on earth were attributed to contamination of the samples through leaks in the transport containers.

Apollo 14 astronauts Alan Shepard and Ed Mitchell with collection bag for moon rocks
(Image: NASA)
The image of the moon, which is completely waterless apart from possibly existing ice on the polar caps, had to be reconsidered after the US space agency NASA in 2010 after the intended impact of a rocket stage and the LCROSS probe on the moon, significant traces of frozen water in one opposite found the crater interior permanently shadowed by the light of the sun. In 2009, data from NASA's Moon Mineralogy Mapper instrument on board the Indian lunar orbiter Chandrayaan 1 indicated the existence of water-containing material that absorbs infrared radiation at certain frequencies. Measurement results from observations of the moon by the US comet probe Deep Impact and a spacecraft on the way to Saturn, the Cassini probe, gave additional indications that water must be distributed far over the lunar surface.

Moonstone, brought to earth by Apollo 14
(Image: USRA / JPL)
Astrophysicists, led by James Greenwood of Wesleyan University in Middletown, Connecticut, re-examined lunar rocks that had been collected during the Apollo 11, 12, 14 and 17 manned missions, focusing in particular on the content of hydrogen isotopes in a particular one Group of water-attracting minerals, the apatites. The quantities found could have three different plausible causes: the hydrogen comes from the moon's mantle below the surface, reached the moon in the form of protons in the solar wind, or was transported to the moon by comets.

The hydrogen traces found in the lunar apatite are very similar to those in the comets Hale-Bopp, Halley and Hyakutake. Comets orbit the sun as reservoirs of frozen water. After the moon formed, which could be the result of a collision of a large rocky celestial body the approximate size of Mars with Earth around 4.5 billion years ago, it was hit by a sufficiently large number of comets. Significant amounts of water got on him in this way.

The distribution of hydrogen isotopes in water on the moon differs from that in water on Earth. The ratio of deuterium (made up of a proton, an electron and a neutron) to hydrogen (made up of a proton and an electron) found in the apatite of the moon is different from that in terrestrial water. Therefore one excludes a contamination of the moon with water from the earth.

Hopes of being able to use the moon as a gas station for space missions at some point are strengthened by the new findings. Since spaceships have to use up to 85 percent of their fuel to leave the sphere of influence of Earth's gravity, the moon could represent a station on the way to other planets. Future planetary missions, for example on the way to Mars, may be supplied with liquid hydrogen and liquid oxygen on the moon, obtained from the water on the moon.

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Source: Nature

Author: Thomas Weyrauch