Pamela Clark

Geochemist Pamela Clark gathers clues about the chemical makeup of other worlds and about how our solar system was formed. She helped develop instruments that measure X-rays coming off the surfaces of planets, moons, and asteroids. These X-rays reveal which elements are present. Clark’s instruments, called X-ray spectrometers, get to their targets aboard spacecraft. By mapping out what elements occur where on the Moon, Clark and her coworkers set the stage for living and working on it.

About Her Life

Pamela Clark (born 1951) grew up in the Connecticut River Valley. Her favorite subject in school was geography. She did not, however, limit herself to reading and playing games related to terrestrial geography; she also expanded her interest to the geography of the heavens. From a young age she had a fantasy of having her own spaceship to find and rescue intelligent beings living in cultures very different from ours and who were in trouble in the universe. When she was about 10, she knew that she wanted to work for the U.S. space program. Those were especially exciting times because President John F. Kennedy had promised to get a man on the Moon in less than a decade. Clark decided she would become the first woman to land on Mars.

In 2000 NASA’s NEAR spacecraft studied the asteroid Eros (left), eventually touching down on its surface—a first in space exploration. Clark’s X-ray instrument discovered that this alien rock is made mostly of magnesium, iron, and silicon.

Moon and Eros photos courtesy NASA. Clark photo courtesy Pamela Clark.

As a 16-year-old, she had an opportunity that confirmed her chosen career path. She was selected to represent the state of Connecticut in a space-exploration camp sponsored by the Girl Scouts and held at the Marshall Space Flight Center in Huntsville, Alabama. There she met Werner von Braun, the great German-American rocket scientist, who insisted that the National Aeronautics and Space Administration (NASA) carry out extensive outreach efforts to schools and colleges.

With the best of intentions, Clark’s family was not truly supportive of her objectives, not understanding why she would want to make her life so “difficult.” It was her teachers who gave her support and encouragement: among them, a sixth-grade teacher who took her interests seriously; a high school biology teacher who let her use the back room of the biology laboratory to study exobiology (the origin, evolution, and distribution of life in the universe); and a chemistry professor at Saint Joseph College in Hartford who, with Clark, analyzed Moon rocks, looking for chemical markers of living systems. Bolstered by her experiences at Saint Joseph, a women’s college where the students were expected to participate fully in the classroom and not hang shyly in the background, Clark went on to graduate from the University of Maryland, where she studied the chemistry of planetary surfaces in order to achieve her long-term goal of working for NASA.

Today, Clark studies the Moon and asteroids using, among other techniques, X-ray spectroscopy. In this technique a beam of X-rays is directed at a sample of material, which then responds by emitting X-rays of its own. Atoms of each element give off different wavelengths of X-rays, and by looking at which wavelengths of X-rays are emitted by the atoms in the sample, a scientist can tell what elements are in the sample.

Here on Earth an X-ray source is used to shoot X-rays at a sample, and a detector is required to pick up the X-rays that are emitted by the sample when the beam of X-rays hits it. These are the main pieces of an X-ray spectrometer, a source and a detector. But in space, where Clark uses X-ray spectrometry, she does not need an X-ray source, because one is already handy—the Sun. The Sun gives off a lot of X-rays. The Earth’s atmosphere blocks them, shielding our planet’s life-forms, but the Moon does not have much of an atmosphere, and asteroids have even less, so they are exposed to the full force of the Sun's X-rays. (This is one reason why astronauts have to wear spacesuits when walking on the Moon—to protect themselves from the X-rays.)

All these X-rays are good news for Clark. Instead of having to fire a beam of X-rays at the things she wants to study, like the Moon, she lets the Sun do this for her. The Sun's X-rays hit the atoms on the surface of the Moon, making them give off X-rays in turn. Using a detector in a satellite sent from Earth to orbit the Moon, Clark can study the X-rays emitted by the Moon's atoms. From these X-rays she can tell which elements are most common in the Moon's crust. She can do the same for Mercury or for asteroids.

Clark had especially good luck when studying the asteroid Eros. When the NEAR spacecraft was sent to the asteroid to study it up close, solar flares erupted from the Sun, sending out especially intense X-rays. These, in turn, caused the asteroid to emit more intense X-rays than usual, so the detectors on NEAR could make exceptionally good measurements of Eros's composition.

In her free time, Clark enjoys a wide range of activities: various nonscientific writing projects, including a cookbook; designing soft sculpture for furniture and fun; writing and performing choral music; studying Irish culture and history; and ministering to prisoners through her church.

For Further Reading on the Web

Flashy Sun Makes Eros Blush for Scientists Using NEAR — news release from NASA's Goddard Space Flight Center.

The Mercury Messenger — newsletter covering recent research on the planet Mercury, edited by Pamela Clark.

Near Earth Asteroid Rendezvous — information on the NEAR space mission from NASA.