Colloquy, the GSAS alumni magazine, is published three times a year and mailed to PhD and master's alumni around the world. It explores the research and impact of Harvard's outstanding faculty, alumni, and graduate students

Margaret Kivelson, PhD ’57, physics, began her career as a physics consultant for the RAND Corporation before deciding she was more suited to a career in academia. Joining the space physics field within ten years of the Sputnik launch, she went on to participate in numerous NASA missions to investigate the outer planets of our solar system.

How did you become involved in space physics?

After I earned my PhD, I worked for the RAND Corporation as a physics consultant, and I did some interesting work while I was there. While my husband was on sabbatical in Boston, I joined him as a fellow at the Radcliffe Institute for Advanced Study, where I conducted research at Harvard and MIT. That year made it clear to me that I would thrive more in an academic institution.

When I went back to California, I spoke to people I knew at UCLA, asking if anybody had a job for a physicist. I was hired by somebody who mistakenly thought I knew something about space physics—and I didn’t disillusion him. I took the job, and it was like starting all over again: I was basically a postdoc, 10 years out. He asked me to help students working on space physics, and the only way I could help was by learning the subject myself. I stayed one jump ahead of them and by the end of a year or so, I had a pretty good background in the field. That was the direction I took with my work, but it was almost by accident.

You are currently working on NASA’s Europa Clipper Mission. Tell me about that.

I’m working on one part of the project that indirectly concerns the magnetometer, on the team called PIMS—Plasma Instrument for Magnetic Sounding. It’s designed to measure low-energy-charged particles in the environment of Europa, which is a moon of Jupiter. That’s critical to the magnetometer because when gases of charged particles surround an object like Europa, the plasma that exists throughout the space around Jupiter and the Galilean moons develops currents that produce magnetic field changes. By measuring the plasma properties, you can correct magnetic field measurements for the currents generated around a moon to determine the magnetic signature of the moon itself. Our team is trying to measure plasma properties to correct the magnetic field measurements and extract from them the signature of the fields generated inside of Europa.

So, without that correction, the data would be skewed, and you wouldn’t get an accurate result?

Yes, because magnetic fields have internal and external origins. It would be very confusing to figure out Europa’s internal field properties otherwise.

If Europa had a permanent magnetic field like we do on Earth, one that is basically stable over thousands of years, we would be able to measure it. The Galileo spacecraft, which orbited Jupiter from 1995 to 2003, took measurements. As far as we can tell, Europa shouldn’t have a permanent magnetic field; nonetheless, each time measurements were made near it, the evidence showed a magnetic field having an origin inside of Europa.

We never know where new knowledge will take us." — Margaret Kivelson, PhD '57 

When we analyzed the data, the best model we could make requires the field to be produced by currents flowing very near the surface—but the surface is ice, and electrical currents don’t flow in ice because it’s a very poor conductor. We needed to figure out what structure within the body could possibly carry electric currents very near the surface. We recognized that a layer of ice sitting on top of a shell of conducting material like an ocean layer of melted ice could explain the magnetic field. It turns out that at the position of Europa, the magnetic field of Jupiter is not constant but changes on an 11-hour time scale as Jupiter rotates. This changing field drives currents in Europa’s ocean and generates what’s called an induced magnetic field. That induced field varies in strength and direction every 11 hours, and we confirmed the expected variability.

Would anything other than an ocean or a liquid do that?

The interiors of these moons are differentiated, with the heaviest, densest material near a metallic core, mostly made of iron. Then, there’s a rocky shell that we call the mantle and beyond that the icy outer shell. If the iron core were melted you could have a similar inductive response, but it wouldn’t have the same intensity.

Gravitational measurements have shown that the near-surface layers are basically a water-ice mixed with other light material like sulfur dioxide, carbon dioxide, and similar traces—but mostly they are water. What the gravitational measurements can’t do is tell you whether or not the water is solid or liquid, but the magnetic field tells us that at least part of the ice is melted.

And by going back, you’ll be able to take measurements that will enable you to answer that question?

By going back we’ll have a lot of new tools that we didn’t have on Galileo. In the first place, we have updated instrumentation, and the plasma measurements we will take will help us extract the signal we’re looking for. But also, we will fly by Europa more than 40 times over a period of several years, so we can look for time-variations other than the 11-hour change that I mentioned. There’s an additional time variation of 84 hours corresponding to the time it takes Europa to go once around its orbit. With those measurements, we will be able to see the induced field from this 84-hour time variation and hopefully figure out how thick the ice shell is on top of the ocean and maybe even how thick the ocean itself is.

What about organic material? If there’s water, then there’s the possibility of life. Is there a way to measure that?

The magnetic field measurements won’t give us answers to that question. But spectroscopic measurements will be taken, which will measure the composition of material that comes off the surface of Europa. Other instruments could conceivably identify either precursors to living material or other chemical compounds consistent with production by living matter. That could tell us what kinds of molecules have developed beneath the surface and bubbled up toward the surface. At some point, the spacecraft might go through a geyser-cloud that would allow it to measure the material being sent up into the space above the surface. So, there are some interesting possibilities.

Looking back on your career to date, what has been the most exciting discovery?

I would say that the discoveries surrounding the Galilean moons of Jupiter are the ones that were the most exciting and unambiguous. Finding a magnetic field at Ganymede and inferring the presence of sub-surface ocean on Europa, I would say, are the top two.

Why do this work?

That’s a good question and a hard one. I believe that we never know where new knowledge will take us. Simply learning anything new about the universe we live in is indirectly beneficial to everybody because, inevitably, we don’t foresee the long-term consequences. To understand how the universe works, what kinds of processes are important, what kinds of processes are present in the bodies of the universe? For example, general relativity was an extremely esoteric refinement when it was first proposed by Einstein. But GPS would not work properly if we didn’t understand general relativity. We never know how new knowledge is going to affect us in practical ways.

But I also think that expanding knowledge has the same effect as creating fine art or building cathedrals. It elevates the spirit, and I think that’s also very important.

Over the course of your career, you’ve advised quite a few PhD students. What do you think makes good advising?

When I go to meetings, I like to seek out the young people and talk to them, find out what they’re doing, take them seriously, and give them advice on whether or not I think they’re going in the right direction or the wrong direction—and I think I’ve managed to do it in a way that doesn’t scare them away. Being interested in what young people are doing and being totally honest with them about the problems they’re working on—I think that is very important.

What advice would you give a physicist who’s just starting her career?

The first thing I would say is that physics is very hard. So, don’t think you’re unique in having trouble understanding some of the concepts and techniques that you’re trying to master. Don’t hesitate to ask for help and try to stick with it. You will get to the point where the ideas make more sense than they do when you’re first introduced to them. It is very easy to become discouraged, so it’s very important to have buddies to talk to—not just faculty, but fellow graduate students as well.

Who inspired you when you were a graduate student?

My advisor was Julian Schwinger, who was a superstar. To me, he seemed to have an unattainable mastery of the field, which certainly gave me a goal to aspire to. And I’m still aspiring.

Elevating the Spirit

Photo by Pamela Davis Kivelson