DONALD V. HELMBERGER
Don Helmberger’s interest in seismology started with a cruise to Alaska — the first time he had ever left Minnesota. After two weeks spent looking at seismic data from the ocean floor, he went from particle physics at the University of Minnesota to seismology at the University of California, San Diego.

Now a geophysicist at Caltech in Pasadena, Calif., Helmberger has academically fathered a slew of topnotch geoscientists who have followed his interests in using seismic waves to see Earth’s core-mantle boundary, theoretically and observationally. Helmberger’s work has illuminated Earth’s inner core, crust and upper mantle using seismology, as well as elucidating earthquake source mechanisms.

RAYMOND JEANLOZ
As a young man who loved the outdoors, Raymond Jeanloz initially “was not at all studying the sciences,” he says. But his first geology course at Deep Springs College near Bishop, Calif., changed that. Now a geophysicist at the University of California, Berkeley, where he is a professor in the Earth and planetary science and the astronomy departments, Jeanloz looks inside Earth through mineral experiments in the lab.

Jeanloz also has worked on National Academy projects, from his first participation in a report on the future of geology in the mid-1980s to his current work with the NAS committee on nuclear arms control and testing. While shuttling between Washington, D.C., and Berkeley, Jeanloz has managed to produce cutting edge research with his graduate students on Earth’s mantle, teach undergraduate students the basics of geology, and serve as editor for a variety of publications.

DENNIS V. KENT
Dennis Kent, according to his former adviser and now fellow NAS member Neil Opdyke of the University of Florida, is “absolutely tenacious” and a “can-do” person. Kent teaches and researches at Lamont-Doherty Earth Observatory of Columbia University and in the geology department at Rutgers University in New Brunswick, N.J. His field is paleomagnetism, but the last 10 papers he wrote, Opdyke says, are all on separate topics, from the magnetism of ice cores to paleogeography. Kent has published more than 200 papers in his career.

Reversals of Earth’s magnetic pole have been a longstanding interest, specifically “to try to delineate precisely the timing,” Kent says. “It’s a beautifully random pattern,” and impossible to predict. Among other landmark research, the paleomagnetic data he collected from the Newark Basin with colleague Paul Olsen helped to establish a global time scale for the late Triassic.

S. GEORGE H. PHILANDER
A meteorologist at Princeton University and one of the “fathers” of El Niño, George Philander calls himself a “child of Sputnik.” At a time when U.S. ocean and atmospheric sciences were getting a boost after the launch of the Soviet rocket, Philander left his home in South Africa to attend Harvard as a graduate student. He took his mathematics background and applied it to ocean data being collected by large international programs in the 1960s and 1970s.

The Atlantic, Pacific and Indian oceans became laboratories for studying oceanic variability, he says, particularly how seasonally changing wind patterns affect currents and waves. In one team project in the Pacific, Philander concentrated on El Niño at a time when the phenomenon was still considered “a regional curiosity” along Peru’s shores. That time “was a wonderful period of exploration,” Philander says, before meteorology, oceanography and El Niño became “big science.”

MARIA T. ZUBER
Planetary geologist and geophysicist Maria Zuber has been observing Mars since she was 10, starting with homemade telescopes. More recently, Zuber has used orbital laser ranging devices and radio tracking systems to look at the planet. Now head of the Department of Earth, Atmospheric, and Planetary Sciences at MIT, Zuber recently participated as a member of the President’s Commission on Implementation of United States Space Exploration Policy, considering a program to send humans and robots to Mars, the Moon and beyond.

Using spacecraft observations, Zuber developed models of the internal structures of Mars, the Moon and Eros (also known as asteroid 433). Her future work focuses on mapping Mercury, Mars and other asteroids, and her research includes theoretical tectonic studies on Earth, Venus and elsewhere.

DAVID J. STEVENSON
Dave Stevenson, who is a New Zealand citizen and was elected to NAS as a foreign associate, is a planetary geologist at Caltech. One of his most recent papers to make a splash was published last year in Nature: a somewhat tongue-in-cheek thought experiment on traveling to the center of Earth (Geotimes, July 2003).

Photo by Beth Coleman, Red Feather Expeditions.

But Stevenson’s more serious work has had a greater impact on planetary origins and other studies. He has considered Europa’s ice shell and Mars’ early plate tectonics, and other issues both closer to and farther from home. He has used data from Galileo and other missions for his work, and only recently has he become more involved in planning such surveys (for example, the proposed Jupiter Icy Moons Orbiter). Stevenson also works on the structure and evolution of the deep Earth and the origin of the Moon.