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Moon, water on
The belief that the dark lunar areas, or maria, might be seas was held by Plutarch and others in the ancient world. In his Siderius Nunctius, Galileo wrote that " ... [the] brighter part most fitly represents its land surface, but its darker part the watery surface ..." Later, he came to doubt this interpretation, but others, including Wilkins, Hevelius, Schröter, and William Herschel kept the idea of a maritime Moon alive for the next two centuries. The demise of lunar water accompanied that of a lunar atmosphere, since liquid water cannot exist where the atmospheric pressure is extremely low or zero. Ice, however, does exist in regions at the Moon's poles. This surprising fact, first suggested by data from the Clementine probe, in 1994, was confirmed, in March 1998, by observations made by Lunar Prospector. After further analysis,1 the initial conservative estimate of 300 million tons was increased by a factor of 10, to 3 billion tons at each pole, enough to fill a lake about 100 meters deep and 6 km across. The possibility also exists that there may be more. The instrument aboard Lunar Prospector used for this determination can detect the presence of water (or, more precisely, hydrogen) to a depth of 0.5 meter. Since lunar soil has been turned over by meteorite impacts during the past couple of billion years to a depth of about 2 meters, water could theoretically be present to this depth. However, if (as suspected) this water exists as crystals mixed in with the lunar regolith, larger amounts of pure water ice deposits could potentially exist at much greater depths.
The lunar ice is thought to have come from comets which collided with the Moon in the remote past. Although most of the water deposited on the lunar surface in this way would have been vaporized long ago by the daytime heat of the Sun, in small, permanently shaded regions at the poles it has evidently survived. Its presence is further evidence that water, frozen or otherwise, is a common commodity on many worlds, and this, in turn, raises the prospects for extraterrestrial life. The availability of water on the Moon is also a major boost to any plans for establishing a self-sustaining lunar colony.
References
- Feldman, W. C., Maurice, S., Binder, A. B., Barraclough, B. L., Elphic, R. C., and Lawrence, D. J. "Fluxes of Fast and Epithermal Neutrons from Lunar Prospector: Evidence for Water Ice at the Lunar Poles," Science, 281, 1496 (1998).
Related categories
• MOON TOPICS
• ASTROBIOLOGY
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