Memorial for Floyd Herbert

On May 12 our long-time colleague and PSI alumnus, Floyd Herbert, a planetary physicist, died in Tucson. Floyd worked briefly at PSI in the 1970s, helping with our experimental program on low-speed rock collisions, between grants at the Lunar and Planetary Laboratory. Floyd studied physics at Cal- tech, taking courses from Richard Feynman, then came to the University of Arizona and obtained a PhD in physics. He was also an excellent photographer who studied with Ansel Adams, an avid motorcyclist, and an ultralight pilot. He was a high school chum and later college roommate of PSI scientist Chuck Wood.

After early diagnoses of serious respiratory problems (and predic- tions of possible death by age 40), he took up karate, studied in Japan, and received a black belt. This was followed by marked improvement in his condition, although it was finally responsible for his peaceful death at age 68.

Scientifically, Floyd worked on issues of magnetic fields interact- ing with asteroids, Io, and extra-solar planets. An innovative example was his 1979 paper in Icarus, with Charles Sonett, then director of the Lunar and Planetary Laboratory at the University of Arizona. Herbert and Sonett analyzed heating of asteroids by strong magnetic fields and solar winds, associated with the “T Tauri” phase of solar system formation. In traditional theories, planetary heating comes from radioactive elements in rock miner- als that would melt asteroids from the inside out, with the largest bodies having the most heating. In the Herbert-Sonett mechanism, however, the heating came from electric currents induced in the surface layers by the magnetic effects of the passing early intense solar wind. The heating would occur from the outside in, involv- ing not just size but also distance from the sun and surface com- position. The Herbert-Sonett model offered an explanation of why some moderate-sized bodies, like Vesta (2.36 AU semi- major axis), have once-melted igneous surfaces, while larger bod- ies, like Ceres (2.77 AU axis), seem to have unmelted primitive surfaces.

The subject of asteroid heating has been somewhat dormant in recent years, but tests of Floyd’s ideas may come with the Dawn mission, now sailing toward both Vesta and Ceres, with the in- volvement of PSI Director Mark Sykes.

At age 49, he met and married the light of his life, Maggie Gilman, creating a wonderful domestic partnership that lasted the rest of his life. Floyd will be greatly missed, particularly for his gentle, wonderful sense of humor.