March 23rd, 2010

I appreciated your article on Professor of Geological Sciences Carle Pieters and the presence of Brown faculty and alumni in lunar studies ("Back to the Moon," January/February). Pieters' experiences as a female scientist in an age of male domination of the physical sciences reflected those of my wife, who is now a renowned specialist in laboratory infrared molecular spectroscopy.

The article also brought back fond memories of the late Professor Tim Mutch, who encouraged me, a ScB physics senior, in 1970, to apply to a relatiely new planetary sciences graduate program at Caltech. I am happy to say that I took his advice and am now one of Brown's pioneers exploring the atmospheres of the outer solar system. I get back to Brown from time to time and have guest-lectured at a seminar organized by Professor of Geological Sciences Jim Head. Like Pieters (and, no doubt, many others), we all look at our spacecraft or ground-based telescope results, at our computer models, or just at the sky at night and say "Oh!" as a three-syllable expression of wonder and elation.

Glenn Orton '70
Arcadia, Calif.

The writer is a senior research scientist at Caltech's Jet Propulsion Lab.



In 1975, I was program manager on a team of Smithsonian and Harvard researchers attempting to map the Earth's gravitational field during the Apollo-Soyuz rendezvous mission. Now, half a lifetime later, Professor Maria Zuber '83 ScM, '86 PhD will be using a similar technique to study the moon's gravity. I hope her team is more successful than we were.

After the 1975 rendezvous was completed, we used radio frequency Doppler signals to measure the distance between the Apollo Command Module and the Docking Module that had linked the two countries' spacecraft. As they circled the earth, any unevenness in the gravity field would cause the separation between the two orbiters to vary. Our results showed far more variations than could possibly be caused by gravity anomalies. It wasn't until some time later that other investigators discovered that the ionosphere was not uniformly spread over the earth. This "clumpiness" had affected our spacecraft-to-spacecraft radio signals and, had we been more imaginative, we might have claimed the discovery as our own.

Chat Watts '54
Tucson, Ariz.



The article featuring Professor of Geological Sciences Carle Pieters was a joy to read. Having worked on the rocks brought back from the moon during the Apollo missions, I remain interested in the search for extraterrestrial water.

I studied the "dust" from the Apollo moon rocks looking for even the tiniest presence of phyllosilicate clay minerals. Because clay minerals have water in them as part of their structure, the finding of native clays on the moon would have been an exciting discovery, but I found none. On the other hand, a group of primitive meteorites known as C1 carbonaceous chondrites contain clay minerals, magnesium salts, and organic matter. They have water contents averaging about 10 percent H2O. The LCross rocket experiment found that about twenty-five gallons of water had been released from the Cabeus crater.

A back-of-the-envelope calculation tells me that one average chondrite about five feet on a side could have provided this volume of water. The impact area in the Cabeus crater was about 80 feet across so just one chondrite would occupy about .5 percent of this area. Can we rule out that the crash didn't vaporize some chondritic material, releasing its water when the crater was bombed? Presumably, the crater itself was the result of an asteroid-type object. Is there a likelihood that some residual material could be left behind and that this water, unlike that seen by M3, is not indigenous to the moon itself? It would seem important to clarify this.

Ken Towe '59 ScM
Eatonton, Ga.

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March/April 2010