November 14, 2003
On television, "As the World Turns" chronicles the lives of fictional residents of an imaginary town. Here at JPL, physicist Dr. Jean Dickey takes the scientific approach to figure out precisely just how our world turns in real life.
Earth's rotation isn't perfectly scripted. It doesn't revolve at a uniform pace. Though a day is measured by how long it takes for the planet to make one complete revolution on its axis, some days are longer than others. Earth also wobbles on its axis, and its gravity field varies
Dickey's challenge, and that of the 9-member research group she leads, is to figure out exactly what forces and processes cause these variations and what they can tell us about the ever-changing Earth. "Everything affects Earth's rotation--the atmosphere, the oceans, topography, the tides, hydrology, earthquakes, polar motion, changes in Earth's core," says Dickey. "This allows us to study Earth as a system. Atmospheric winds, for example, cause most of the variation in Earth's rotation on timescales of a year or less – in fact, we even use weather forecasts to help predict changes in Earth's rotation."
In her sunny office, decorated with bright Impressionist prints and her own colorful photographs, Dickey spends a lot of time thinking about what goes on inside one of the darkest spots on Earth—its core. How fast or slowly Earth spins is determined by how its mass, made up of the atmosphere, the solid Earth and its fluid core, is distributed. While some variations in Earth's rotation rate last only a few weeks or a few years, some can last decades. "These very long time changes are too big to be caused by atmosphere or oceans," says Dickey. "They are the result of movement of fluid within the core, which changes Earth's mass distribution." She has published a number of papers on the subject.
Earth's gravity field is another of Dickey's research interests. Analyzing changes in gravity led to a recent paper in Science in which she and three colleagues offered an explanation for why Earth's waistline appears to be thickening. "Some people refer to it as equatorial obesity," she says. "Water has moved from the poles to Earth's midsection as a result of glacier melting and changes in ocean circulation." Dickey led a National Resources Council study on time-variable gravity, a critical tool for oceanography and solid Earth sciences. She served as president of the geodesy section of the American Geophysical Union.
Dickey's JPL research group also has a job that is particularly important to the Lab. They use the most advanced measuring techniques to determine Earth's precise orientation and what it will be at a particular time in the future. "We supply data to all the JPL missions," says Dickey. Without this information, it would be impossible to navigate spacecraft, which use Earth as a reference point for their maneuvers. "For example, Mars Pathfinder needed near real-time data for its insertion into martian orbit. The entry angle is critical--too much in one direction and the spacecraft will burn up, and too much in another direction and it will be deflected from the planet."
Dickey didn't set out to be a specialist in geodynamics and Earth rotation. The second of six children, she grew up in the suburbs of Pittsburgh, Penn. "Two thirds of the people worked in the steel mills," she says. "My father was an architectural designer for the G.C. Murphy chain of stores, but deep down he was an artist and a poet. My mother was very good in math, but times were different then, and she had her hands full with six kids."
All six graduated from college, although neither of their parents did. "We all have done something different," says Dickey, the only scientist in the group. Two of her siblings are teachers, two are in business, and one is an economist.
Like her mother, Dickey was interested in math and science. "It seemed clear to me as a way to move ahead." She went to a small liberal arts college, now St. Francis University, first studying engineering and later switching to physics. She got her first taste of the scientific life when she entered an honors program at the U.S. Department of Energy's Argonne National Laboratory in her senior year. Dickey completed her Ph.D. at Rutgers University in high-energy physics then served on the research faculty at the California Institute of Technology ("also known as physics heaven on Earth," she says) before moving to JPL in 1980.
When she's not working, Dickey enjoys tennis, photography, aerobics and walking. "I love art and going to botanical gardens. I'm also very fond of snorkeling in Hawaii," she says. "I could do that as a full-time job."
After more than 20 years at the laboratory, Dickey says, "I like interacting with the people here; they are very open to talking about what they're doing and they appreciate what we do. There is a great wealth of knowledge at JPL. I can look around the lab for expertise in many different areas."