Eugene M. Shoemaker

American geologist and planetary scientist

• Born: April 28, 1928; Los Angeles, California
• Died: July 18, 1997; Alice Springs, Australia

Twentieth-century geologist and planetary scientist Eugene Shoemaker pioneered the field of astrogeology, the study of the geological makeup of celestial bodies. In the 1960s, he was involved with the first unmanned missions to the moon and provided geological training to Apollo astronauts. He and his wife discovered numerous comets and asteroids during their careers, including the Shoemaker-Levy 9 comet that collided with Jupiter in 1994.

Also known as: Gene Shoemaker

Primary fields: Astronomy; Earth sciences

Specialties: Geology; astrophysics

Early Life

Eugene Merle Shoemaker was born on April 28, 1928 in Los Angeles, California. A gifted student, he graduated from the California Institute of Technology (Caltech) in Pasadena at age nineteen. A year later, he earned his master’s degree there, after completing his thesis on a study of Precambrian metamorphic rocks.

Also in 1948, Shoemaker began his lifelong involvement with the US Geological Survey (USGS). While conducting his first fieldwork for the USGS, looking for deposits of uranium in Utah and Colorado, he became fascinated with the idea of space exploration. As he read of experiments the US government was then doing with seized German V-2 rockets, Shoemaker was inspired to explore the possibility of a manned moon mission.

Shoemaker theorized that the moon’s craters were formed by the impact of asteroids and volcanic eruptions. In 1952, he traveled to Meteor Crater in Arizona. The 4,000-foot-wide depression was among the most recent meteor impact craters on Earth. As he made the first comprehensive geological analysis of the crater, he became convinced that it—like the larger craters on the moon—had been formed by the impact of an asteroid. His analysis of Meteor Crater also helped solve a scientific riddle. If a meteor had formed the crater, why had no such object ever been found? Shoemaker concluded that a 150-ton iron meteorite had crashed in Arizona 50,000 years ago and was instantly vaporized in an explosion equal to the force of a 20-megaton nuclear bomb.

Shoemaker earned his second master’s degree at Princeton University in 1954 and his doctorate in 1960, for which he wrote a thesis on his work at Meteor Crater. In 1951, he married the former Carolyn Spellman, with whom he had three children.

Life’s Work

As a geologist, Shoemaker looked at the ways in which violent explosions shaped their impact sites. With the USGS, he studied volcanic processes, observing that uranium was often located in the eroded vents of ancient volcanoes. He also surveyed the craters left after the test detonations of nuclear weapons under Yucca Flat in Nevada. He soon realized the characteristics of craters made by nuclear detonations were similar to the ones he had observed at Meteor Crater. While researching the mechanics of meteor and nuclear impact craters, he and geologist Edward Chao discovered coesite, or shocked quartz. This type of silica forms under tremendous pressure and is ejected in a ring pattern following a violent impact.

In 1961, Shoemaker got his chance to do pioneering work in the field of astrogeology when he was tapped to head the Astrogeology Research Program of the USGS at Flagstaff, Arizona. This was the same year that President John F. Kennedy committed the National Aeronautics and Space Administration (NASA) to mounting a manned moon mission by the end of the decade. As head of the program at Flagstaff, Shoemaker was involved with the unmanned Ranger and Surveyor missions to the moon. He also helped train the astronauts in geological science. Shoemaker wanted to become the first geologist on the moon—despite the fact that NASA was considering only trained pilots, and not scientists, as astronauts. In 1963, he was diagnosed with Addison’s disease, an adrenal gland disorder. The diagnosis disqualified him from becoming an astronaut.

In 1964, Shoemaker and his staff at USGS used telescope images to draft the first geological lunar map, as well as outline geologic time on the moon. For this work, Shoemaker is credited with laying the foundations of lunar geology as a scientific discipline.

In 1969, Shoemaker became a professor of geology at Caltech, where he served as Chair of its Division of Geology and Planetary Sciences for three years. He began to study comets and asteroids that crossed Earth’s orbit. He became convinced that an impact from one of these celestial bodies could wipe out most life on Earth. Many scientists theorize that a comparable event ended the age of the dinosaurs 65 million years ago. Shoemaker advocated that astronomers systematically track these objects and develop an “early-warning system” in order to prevent a calamity from occurring. Shoemaker, along with Eleanor Helin, provided a plan to track the Apollo asteroids, some of which formed the impact craters on Earth and the moon. The search program was operational by 1973.

Shoemaker studied and tracked celestial objects with the 18-inch-diameter telescope at the Palomar Observatory outside San Diego, California. Beginning in 1980, his wife Carolyn worked alongside him, studying images made from the films taken at the Palomar Observatory. Three years later, the Shoemakers discovered their first comet together. In all, the discovery of over thirty comets and over one thousand asteroids would eventually be credited to this trailblazing team.

The couple’s most famous discovery occurred in March 1993. Along with their colleague, Canadian astronomer David H. Levy, the Shoemakers found an extraordinary comet in the outer solar system, which had come within sixteen thousand miles of Jupiter. At the time of its discovery, the Shoemaker-Levy 9 comet had been ripped apart by Jupiter’s terrific gravitational pull, and its fragments began being pulled inexorably toward Jupiter. Astronomers across the world watched in amazement for four days beginning on July 16, 1994, as twenty fragments from the comet fell into Jupiter’s atmosphere, resulting in tremendous fireballs.

Although Shoemaker retired from his professorship at Caltech in 1985 and from the USGS in 1993, he continued to work at the Lowell Observatory in Flagstaff, traveling around the world to study impact craters. On July 18, 1997, during an expedition to Alice Springs in the Northwest Territory of Australia, Shoemaker was killed in an auto accident. His wife was severely injured in the crash but survived to continue working in astronomy. In July 1999, some of Shoemaker’s cremated remains were sealed in a small capsule designed by planetary scientist Carolyn C. Porco and sent to the moon aboard the unmanned Lunar Prospector spacecraft.

Impact

Shoemaker is credited with creating the discipline of astrogeology, or planetary science. Prior to his lifetime, such work was considered part of astronomy as a whole. His application of geological fundamentals to the study of celestial bodies revolutionized the way scientists map planets, moons, asteroids, and comets. His work influenced the Apollo missions and continues to have an impact on the work of unmanned probes sent deep into the solar system by scientists to learn how the planets evolved and how their geology played a part in that evolution.

Shoemaker’s fieldwork at Meteor Crater and other impact sites highlighted the importance of celestial impacts on the development of Earth’s geology. Shoemaker also helped to popularize the theory of a meteor event leading to the extinction of the dinosaurs.

Yet Shoemaker’s most significant contribution to science is also his most famous: his codiscovery of the Shoemaker-Levy comet, which provided astronomers with a key opportunity to learn about both a comet’s dynamics and the planetary science of Jupiter. For the first time, scientists witnessed two celestial bodies colliding in Earth’s solar system. Shoemaker-Levy’s collision led many astronomers to theorize that Jupiter may act as a kind of “cosmic vacuum cleaner” for the inner solar system and protect Earth from more frequent meteor impacts like the one that wiped out the dinosaurs.

Shoemaker received numerous awards throughout his career. Among his most notable are the Wetherill Medal from the Franklin Institute in 1965, the Gilbert Award from the Geological Society of America in 1983, and the Kuiper Prize from the American Astronomical Society in 1984. In 1980, he became a member of the National Academy of Sciences. In 1992, President George H. W. Bush presented him with the National Medal of Science, the nation’s highest scientific honor.

Bibliography

Chaikin, Andrew. A Man on the Moon: The Voyages of the Apollo Astronauts. New York: Penguin, 2007. Print. Presents a comprehensive overview of the Apollo missions that sent US astronauts to the moon in the late 1960s and early 1970s. Provides information about the missions themselves, reviewing biographical information about Shoemaker and describing his contributions to the US space program.

Faure, Gunter, and Teresa M. Mensing. Introduction to Planetary Science: The Geological Perspective. Dordrecht: Springer, 2007. Print. Provides an analysis of Earth’s solar system and demonstrates how Shoemaker helped scientists to better understand it. Includes numerous recent photos, including images taken by the Cassini-Huygens probe and the Hubble Telescope.

Levy, David H. Shoemaker by Levy: The Man Who Made an Impact. Princeton: Princeton UP, 2000. Print. Full-length biography of Shoemaker, delineating his contributions to planetary science throughout his long career.