Pete Waller (retired) May 18, 1967
NASA Ames Research Center, Moffett Field, Calif.
CLUES TO ORIGIN OF THE MOON WILL COME FROM STUDY OF THE FIRST LUNAR SAMPLE
Indications of whether the surface of the Moon is made of rocks like those on the surface of the Earth, or of material with a different distribution of elements will come from the first sample of lunar soil.
Though it may raise many new questions, the lunar material to be brought back by the Apollo astronauts should provide important evidence on origin of the Moon and solar system.
Dr. Klaus Keil, geochemist at NASAÕs Ames Research Center near San Francisco, will determine distribution of elements in lunar minerals, plus crystal lattice structures in the lunar material. He is one of 110 principal investigators from the U.S. and abroad, chosen to study portions of the first lunar sample.
Dr. KeilÕs co-investigators are Drs. Theodore Bunch and Kenneth Snetsinger, post-doctoral fellows of the National Academy of Science, working at Ames, and Dr. James Short, U.S. Geological Survey, Menlo Park, Calif. They will use an electron microprobe to determine chemical composition of the sample.
This device bombards samples as small as a few thousandths of a millimeter in diameter (dust particle size) with a narrow electron beam to analyze in detail the minerals it contains. Electronic microprobe analysis does not damage the sample appreciably, and the material can later be used for other studies.
Dr. Keil currently does similar work with meteorites (space rocks believed to come from the asteroid belt). He has recently discovered a new extraterrestrial mineral in a meteorite, which contains clues to the conditions under which the meteorite rock was formed.
Many scientists believe that the Sun and planets condensed from a cloud of gas in space made principally of hydrogen, but with other elements. The Sun is believed to have formed about six billion years ago, the planets about 4.5 billion years ago.
The near-planets (Earth, Mars, Venus) are believed to have lost their hydrogen and other volatile elements because of solar heat. The outer, colder planets (Jupiter, Saturn, etc.) kept these volatile elements and, therefore, are much bigger.
Chemical analysis of the lunar sample may provide clues as to whether the Moon was formed along with the Earth in this process.
The picture is complicated because internal volcanism and atmospheric erosion have greatly changed the Earth since its formation. No original 4.5 billion-year-old rock has been found on EarthÕs surface, although rock 3.5 billion years old has been located. Furthermore, during the EarthÕs geologic evolution, various elements are believed to have separated out on an enormous scale (i.e., the EarthÕs assumed nickel-iron core).
Similar changes may have occurred on the Moon, although these are believed by many scientists to have been far less drastic. And distribution of elements on the lunar surface may be similar to their distribution in the whole Moon.
Pressure and temperature conditions of formation of lunar minerals and rocks can be inferred from electron microprobe data. Knowledge of these conditions may be used to estimate the extent and nature of volcanic activity, or heating and fracturing changes caused in rocks by comet or meteoroid impact. Many of these interplanetary projectiles strike the Moon at around 27,000 mph, producing pressures of many millions of pounds per square inch under the impact point and temperatures high enough to liquefy several times as much rock as the mass of the meteorite itself.
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