Benjamin P. Weiss

2009 James B. Macelwane Medal Winner

Massachusetts Institute of Technology

Peter J. Huybers, Miaki Ishii, and Benjamin P. Weiss were awarded the 2009 James B. Macelwane Medal at the AGU Fall Meeting Honors Ceremony, held on 16 December 2009 in San Francisco, Calif. The medal is for “significant contributions to the geophysical sciences by a young scientist of outstanding ability.”


I am delighted to present Benjamin P. Weiss as a recipient of the 2009 AGU James B. Macelwane Medal. Ben is an extraordinary scientist whose career got off to an early start when, as a high-school senior, he was selected as the youngest-ever principal investigator for the Hubble Space Telescope.

As a graduate student at California Institute of Technology studying with Joe Kirschvink, Ben demonstrated that the only truly ancient (~4 Ga) Martian meteorite, ALH84001, was blasted off Mars and transported to Earth without being heated enough to thermally sterilize its interior. This research demonstrated the potential viability of transporting microbes between planets. However, during the frenzy around the announcement that ALH84001 contained magnetofossils indicating ancient bacterial life on Mars, Ben remained admirably objective and published evidence against the presence of bacterial magnetosome chains in this meteorite. He further demonstrated that ALH84001 preserves stable magnetic remanence and showed that the paleointensity of Mars’s early magnetizing field was within an order of magnitude of Earth’s present field. Soon after arriving at MIT, Ben and David Shuster used measurements of argon loss to demonstrate that the surface of Mars over most of the past 3 billion years rose to temperatures just above freezing but was never particularly clement. This result represented a tangible advance in understanding Martian climatic history.

With Franz Baudenbacher, Ben greatly improved the technique of superconducting quantum interference device (SQUID) microscopy, pushing the technology to levels never before achieved in paleomagnetism. With postdoc Eduardo Lima, Ben instituted a new inversion approach that allows the full magnetic moment vector to be derived from the measured vertical component using Maxwell’s equations.

Ben used his recently completed paleomagnetic facility at MIT to document stable remanent magnetization of angrites, a class of basaltic achondrites derived from a parent body from the main asteroid belt. The meteorites reveal thermoremanent magnetization that dates prior to 4.55 Ga and that persisted over a time longer than the expected lifetime of the circumsolar disk. He argued persuasively that the data represent evidence for a core dynamo in an accreting protoplanet, changing the paradigm for how planets accreted from the solar nebula.

Recently, Ben identified the only known ancient Apollo sample of the lunar highlands that was both unshocked and not otherwise magnetically altered subsequent to crustal emplacement. He argued that the ancient age, magnetic intensity, and time scale over which the sample was magnetized provide collectively the first quantitative evidence that the Moon once had a core dynamo. While not the final word, this study goes a long way toward resolving the enigmatic magnetization of Moon rocks.

Ben has revitalized the field of planetary paleomagnetism by improving instrumentation and analysis techniques and addressing confounding problems. His modus operandi of combining paleomagnetism with thermochronometry has allowed him to revolutionize understanding of magnetism in the context of thermal histories of solar system bodies. For an impressive array of discoveries and a rate of scientific progress that makes one a believer in warp speed, Ben is indeed a worthy recipient of AGU’s Macelwane Medal.

—MARIA T. ZUBER, Massachusetts Institute of Technology, Cambridge


Thank you, Maria, and thank you very much to AGU for this recognition. I got into this business of planetary science just after my junior year of high school. That summer, in Ojai, Calif., I heard a talk about how the institute director of the newly launched Hubble Space Telescope, Riccardo Giacconi, had donated a few percent of his observation time to the amateur astronomers of the world. Well, a few of us kids in the audience applied to use the Hubble to look for asteroid satellites, and lo and behold, we were granted a few hours of observing time. The excitement that followed has never left me and is a major reason I am in science today. Thank you to Riccardo and to those at the Space Telescope Science Institute who helped make this possible. And thank you to my parents, who got me to Ojai, and to Earth, in the first place.

Because I had been mainly playing with telescopes, when I got to graduate school I knew next to nothing about paleomagnetism or, for that matter, about rocks. But then I heard about a character named Joe Kirschvink, who had named his son “Magnetite,” who considered it an entirely reasonable possibility that humans have innate magnetoreception (a “sixth sense”), and who was studying a 4-billion-year-old rock from Mars that some people thought contained fossils of Martian organisms. Even though some of this sounded too good to be true, I thought this guy sounded like my kind of advisor. So while I was a second-year grad student, Joe gave me, with virtually no strings attached, exclusive access to his cherished supply of Martian meteorite and a bunch of interesting ideas to look into, and then stepped back and let me run with it. In the meantime he taught me geology, paleomagnetism, and most important, how to take strange ideas just seriously enough that they can get their fair chance to shine. Without Joe’s patience, inspiration, wit, and bottomless support, I would certainly not be standing here today.

I also would not be here without Maria Zuber, Ron Prinn, Sam Bowring, Tim Grove, and the other faculty at MIT. They took a chance by hiring me even though I suspect paleomagnetism was not in their 5-year plan. My ability to make good measurements is founded on the beautiful lab they patiently helped me construct and the collegial and intellectually vibrant environment they have fostered at MIT. Of course, instruments are useless without great users, and for that I am indebted to Eduardo Lima and Laurent Carporzen and the many other amazing scientists and students with whom I’ve been lucky to work. Much of my basic approach for understanding the thermal stability of the rock record was developed in collaboration with my mentor of all things gaseous and noble, my friend David Shuster. Finally, I would be nowhere without the love and honest criticism of my wife and fellow cosmic explorer, Tanja Bosak. Thanks very much for this great honor and for being here tonight with me to celebrate it.

—BENJAMIN P. WEISS, Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge