Earth & Planetary Science Graduate Student Leads Moon Research

By Genevieve Shiffrar, January 28, 2003

Around the world, people have been reading about an exciting new theory to describe the early history of the moon. It is an engaging story that speaks of blankets and burps, of astronauts' moon walks, and that elusive "Man in the Moon" character who smiles down at us every full moon. Yet, few people know that the lead scientist behind this revolutionary finding is an unassuming graduate student in the L&S Department of Earth and Planetary Science.

Dave Stegman, seated at right, with collaborators Mark Jellinek (left) and Mark A. Richards (center).

Dave Stegman collects the newspaper articles from France, Australia, Germany, India and elsewhere to keep for his parents. Among his favorites is the story written by Roger Highfield for the UK's The Sunday Telegraph, How a burp made the Man in the Moon. UC Berkeley science writer Robert Sanders gives a more technical overview, Moon's early history may have been interrupted by big burp.

Dave and his collaborators developed a computer model of the moon which incorporates an understanding of the deep interior of planets. The team theorizes that a blanket of hot rock rose up from the molten core of the young moon like a blob in a lava lamp. Resultant rapid cooling of the metallic core led to a magnetic field being generated inside it. When the burp of hot rock reached the surface, it melted and formed a giant pond of hot liquid magma, which spilled out over basins of the moon's crust giving birth to the Man in the Moon. Previous scientists had hypothesized that the Man in the Moon originated from the center of the moon as a blob of hot, partially molten rock. This new research reinforces the idea by providing a credible scenario for a short-lived lunar magnetic field.

To hear Dave recount the steps he and his colleagues took in developing this idea reconfirms the power of collaboration and interdisciplinary inquiry.

When Dave arrived at Berkeley, he wanted to study the evolution of planets. His advisor, Mark A. Richards, suggested that he work on extending the capabilities of a computer model originally developed by John Baumgardner from Los Alamos National Laboratory. For several years, Dave focused much energy on improving the software for more nuanced understanding of the internal dynamics of planets.

Dave generally assumed that the software would model the Earth's dynamic interior. But then three things happened almost simultaneously to change and expand the investigation.

First, he attended a seminar organized by Professor Imke de Pater in the Astronomy Department. There, it was mentioned that the moon at one time might have had a magnetic field, as evidenced by the magnetized rocks collected by Apollo astronauts. According to Dave, "What struck me was a peculiar thing about that ancient lunar magnetic field, other than the fact that a planet like the moon generally shouldn't have a magnetic field at all, was its apparent sudden onset. If something like that happened, it had to be something really weird. It was a total mystery. No wonder most people rationalized the data was wrong."

Second, he participated in a graduate reading group organized by postdoctoral researcher Mark Jellinek to discuss magma chambers below volcanos. At the time, Dave says he wasn't particularly interested in problems of that small size. He was more interested in large-scale planetary changes, so he tried to "scale up" the ideas. Together, he and Jellinek started to theorize about the moon's early conditions and how the moon may have solidified from a molten state. They imagined a vast magma ocean instead of a volcanic magma chamber. Looking back, Dave says, "These were just fun things to think about together."

In the third step, the computer modeling program finally started to function well, and Dave decided to apply it towards understanding the moon's history. Calculations needed to be performed on a super-computer and the team was able to use one at the NASA Goddard Space Flight Center in Maryland. Many scientists compete for its use so access to the machine was limited. Dave regularly would get up at 4:00 am to run calculations before those on the East Coast logged on to start their own day's work.

Thus began a period of experimentation with the model. At one point, a glitch in the software sparked in him a "mini epiphany." He immediately wanted to share his idea with collaborator Stephen Zatman, who was then a Miller postdoctoral fellow in the department. Perhaps the moon did not have in the beginning a magnetic field because a thermal layer of dense radioactive elements covering the moon's core moved heat both into the core and away from the core. (Only when the layer reached a sufficiently high temperature could it lift off the core. This could have started a cooling process whereby a magnetic field could develop.)

Stephen Zatman's infectious enthusiasm made it easy for Dave to call him up that evening. As a specialist in core dynamics and magnetic fields, Zatman confirmed that this process could happen. Zatman always encouraged Dave and other Berkeley graduate students to bounce around ideas with him, even after he had left Berkeley to move on to his new post as an assistant professor at Washington University in St. Louis. Tragically, Stephen Zatman passed away unexpectedly before the publication of this research. According to Dave, he was "the most fun person" he has ever worked with; "He simply loved this stuff."

The spirit of generosity so characteristic of Stephen Zatman, as well as that of all the collaborators, made the research possible. Putting it all together—the programming, the data, the theory—required a team effort. Dave Stegman is the first to declare that, as a graduate student working on such a far-reaching and interdisciplinary project, there was "no way I could have done this without all of my co-authors."

The result? Our understanding of the early history of all planets may be altered forever.