Black and White Program

Dr. Dan Lathrop: The study of the Earth’s magnetic field

July 3rd, 2008 by John Eastman

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For over a decade, University of Maryland geophysicist Dr. Dan Lathrop has been on a quest to construct and run tests on spherical models that simulate the physics of the Earth’s magnetic field. Now completing work on the fourth model, his academic group is close to their biggest feat yet: filling the rotating sphere with sodium to create a self-generating magnetic field. These tests will contribute to our understanding of the inner workings of the Earth’s core, which in turn alters our approach to dealing with the effects of solar radiation. Black and White talks with Dr. Lathrop about his work and influences.

Welcome to Black and White. I appreciate you taking the time to do the interview.
LATHROP: I’m happy to help you.

You are a geophysicist at the department at the University of Maryland?
LATHROP: I actually am faculty in two different departments, physics and geology, although the research I do, at least half of it is geophysics. There’s no proper department with that name.

Three meter diameter sphere and researchersThis project is designed to help identify how the earth’s magnetic field is generated?
LATHROP: Yes. In particular, we’d like to understand how it’s generated and use the experiments to help build a science of the earth’s magnetic field because there is no current way to predict where the earth’s field is headed and going to forecast right now.

I’m going to come back to the project itself in a second, but I want to talk to you about your background first. What made you want to become a geophysicist? How old were you when you made that decision to enter that field? What influenced you?
LATHROP: There is not a short answer to those questions. I grew up in a family where my father was an engineer and the family often spent time outdoors, actually doing some rock hunting. So I grew up in a situation of being interested in the earth. And I started out in college as a mineral engineer, to start with, at UC Berkeley, but then nearly switched to geology, and in the end, finally switched to being a physicist, although under somewhat strange influences. The course that convinced me to become a physicist was a geology course. It was taught by Walter Alvarez, a professor at Berkeley in geology who was the son of Luis Alvarez, who was a Nobel Prize winning physicist at Berkeley. But the way that Walter taught his geology class interested me quite a bit in physics in the end. So I went on to get undergraduate degrees in physics, and then a PhD in Physics from UT Austin, mostly studying turbulent flood flow. But when it came time to become a faculty member, I was looking for different projects that I might set out on my own to do. And I learned about the possibility of doing experiments to understand the earth’s magnetic field and that was very attractive to me. Ed Bolton, who is a geophysicist at Yale, was the first to suggested it to me, when I was a post doctorate at Yale at the time. And just over lunch one day, he and I were brainstorming about what it is I should do as a young faculty member, if I could get a position. And that was one of the projects that he said he thought was possible but challenging, and I guess I liked that part of it.

Was there a key person at that time in your developing professional career who may have influenced you to become a geophysicist?
LATHROP: Well, the pivotal character that caused me to almost go into geology and, in the end, into physics was Walter Alvarez when I was an undergraduate. So, with faculty in physics and also faculty in geology, I have quite a bit of leeway as to the different areas I could work in. And those early influences then steered me towards geophysics. Another major influence was Harry Swinney, my Ph.D. adviser at the University of Texas. He taught me how one might design experiments such that they might yield unexpected results. This has been especially important in my work through the years.

When you were young, what were you interested in?
LATHROP: Oh, I guess, as a kid I was definitely prone toward tinkering. And so my father would often give me things to take apart. And I would take them all apart and save some of the parts and then combine parts together into other devices. I think more or less, I was raised to be an engineer. I think my father really had that vision in mind. I think he was a little bit surprised by the change of direction, but he got used to it.

Still in the lab, now, when we build these things, we’re designing things from scratch and putting them together and debugging them as such. There’s definitely a tinkerer’s aspect to being an experimental physicist.

This is your third sphere that you’ve built?
LATHROP: The fourth, actually. Well, the first one was not spherical, but it’s the fourth of the line as experiments of this sort, the fourth sodium experiment.

How long have you been working on this project?
LATHROP: Oh, goodness. I’m going to feel old talking about it. Well, the first idea was probably around in ’93, maybe spring, ’94. And then I became an assistant professor in faculty that — later that year in ’94. I didn’t start sodium experiments probably until ’96. So it’s probably been about 12 years now working on sodium experiments, all of them with the same set of goals in mind, to understand the earth’s magnetic field.

What have you learned? What progress has led to this latest one?
LATHROP: Well, in each case we’ve taken steps toward larger experiments with higher input power. And in each stage along the way, we have seen in experiments that have not generated their own magnetic field, but would respond to an external magnetic field and to the rotation to give magnetic fields and to give the sort of fluid motion inside that have pointed the way toward more earth-like models.

So the first several didn’t generate the magnetic field, but they responded to outside magnetic fields?
LATHROP: Right. For those first experiments, if you applied an external magnetic field, ones from the outside, they would then respond by generating a magnetic field of their own, but only while that outside field was present. They weren’t– and believe me when I use this– they weren’t dynamos by themselves, but they would induce magnetic fields from an outside source. But if you spoke to them, they would speak back. But they wouldn’t just start chattering on their own.

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