American physical chemist (1893-1981) whose pioneering work on isotopes earned him the Nobel Prize in Chemistry in 1934; he also played a significant role in the development of the atomic bomb. TLS, one page, 8.5 x 11, University of California, San Diego letterhead, November 17, 1972. Letter to Dr. Howard Sharpe of the Lunar Science Institute, in part: "I have been going over your letter, and I find it difficult to know exactly what to say. What impresses me is that you can make a completely melted moon and can cool it down sufficiently to make it strong enough to support the mascons. My question, of course, is when the mascon landed on the moon. I had supposed this was approximately 4.6 b. y. ago, but now it looks as if it is 4.0 b. y. ago. Can one cool down a completely melted moon sufficiently to support these things at that time? I have my doubts about it.
Also, it seems to me that you will have difficulty solidifying these surface regions of the moon, at least the seismologists think there is a low density layer going to a depth of 60 km, but after that, to dunite, and solid dunite is more dense than the liquid. Therefore, it would not float on the surface in the way you have postulated. I am not sure that the seismologists are right because of the limited area they have investigated and may be peculiar in some way because of the great mascons in that neighborhood. Apparently Apollo 17 is not going to help in this matter at all, since it is right on the edge of a big mascon…I am immensely puzzled by the whole problem of the structure of the moon at the present time." In very fine condition. Accompanied by the original mailing envelope.
Harold Urey was one of the foremost planetary scientists of his time. In 1972—as now—there was considerable debate concerning whether the moon formed hot or cold. The "mascons" that Dr. Urey refers to were enormous subsurface mass concentrations left over from the asteroid-like objects that formed the mare regions of the moon that give us the face of the 'man in the moon.'
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