Natural base on the Moon: the Lava Tubes
In the future, the Moon will change from an object to explore to become a base for mankind's activities. The problem is whether mankind can cope permanently with the Moon's harsh environment. It seems that the Moon has already provided a candidate for a splendid natural base. It is the caves called lava tubes. The lava tubes are formed when lava erupted from volcano flows. The lava flow makes a cave. There are many lava tubes in Japan, for example, in Aokigahara at the base of Mt. Fuji. On the Moon, there are areas where craters lie in a row (see Fig. 3). The formation of such areas can be explained thus: a tube is formed beneath the area, but the tube's ceiling is hit by small meteorites and collapses, forming a line of craters. In the lunar lava tubes, equipment and personnel can be protected from meteorites and/or cosmic rays. Temperature changes on the lunar surface that vary up to hundreds of degrees Celsius would not reach the lava tubes. According to the study by Miyamoto (University of Tokyo) and the author, the temperature inside the tube is likely to be kept at about 0 degree C. Moreover, the bottom of the tube is smooth so we can walk without much trouble. In addition, the larger lunar lava tubes are believed to extend hundreds of meters in width and tens of meters in height. Such safe, huge spaces are naturally provided on the Moon. If there are tubes with height up to tens of meters, the Terrain Camera of SELENE may find the entrances.
The chain of dotted craters indicated in Fig. 3 is also seen on Mars (Fig. 4). It is believed that Mars had (or has?) water underground. If water exists in the surface layer, it must flow in the tube. There is possibility that water flows and dries up in the tube repeatedly. This suggests that the tube might be a suitable place for life to emerge due to its environment: water is moderately supplied, temperature is stable, and it is protected from radiation. Since the Moon has no atmosphere, oceans, and forests, it is very suitable place to observe spread and shape of the lava tubes broadly. Investigation of the lava tube on the Moon must be linked and develop to research on lava plateau formation on solid planets produced by the tube formation, exploration of the Mars's tubes, and quest for life in the tubes in the future.
Due to space limitations, this article has to end with the introduction of some specific expectations for lunar exploration. In SELENE, a variety of data will be obtained and various research studies will be made, though I cannot introduce all of them here. The data and studies will become important for the 21st century's planetary science. Also, the data obtained by SELENE will be basic ones for those who will again visit the Moon.
Everybody, shall we return to the Moon!
(This article is excerpts, edits and expands on a paper published in “Viva Origino (Vol. 30, No. 3, p138-143, 2002)” by Junichi HARUYAMA, with kind permission of the Society for the Study of the Origin and Evolution of Life JAPAN.)