By Emily Levesque, University of Washington
While studying asteroids and comets, it’s easy to think of astronomy as an exceptionally distant science. Still, for very close objects in the solar system astronomy can move beyond studying light and gravitational waves, and include the geological aspects. One can ask geological questions, send probes to look at them up-close, and gather samples to study in a lab. This type of research is known as planetary science.
The Curious Case of a Crater
Planetary science grew in part out of geology research here on Earth and a puzzle that faced geologists in the middle of the 20th century.
It was a puzzle caused by an asteroid, or rather what used to be an asteroid.
About 35 miles east of Flagstaff, Arizona, is an enormous crater. Three-quarters of a mile across and 560 feet deep, its presence had fascinated geologists for decades. In 1960, most geologists believed that it had been caused by a volcanic explosion.
However, a few remained unconvinced, and were fans of an earlier and less popular theory: they thought the crater had been caused by some kind of impact from space. The impact theory was still around, albeit unpopular when a young geologist named Gene Shoemaker began to study the crater.
Gene Shoemaker
At first, Shoemaker’s work had nothing to do with astronomy; he studied uranium deposits and the geology of volcanic vents. His research led him to northern Arizona and, eventually, the immense crater near Flagstaff.
The crater fascinated him so much that he made it the subject of his doctoral thesis at Princeton. Shoemaker recognized that the crater bore a strong resemblance to craters formed during atomic bomb testing.
Findings from Gene Shoemaker’s Study
When Shoemaker and his colleagues began studying the chemistry of the crater, they recognized minerals that could only have formed in the high temperatures and pressures of a tremendous impact. They reported that the crater had not been formed by a volcano. It had been formed by a meteor.
The meteor that formed Arizona’s crater would have been much bigger, producing a brilliant multi-colored streak as it incinerated in the atmosphere, culminating in a cataclysmic impact, and leaving behind the rocky remnants we know today as “meteorite finds”. The crater in Arizona is now famously known as Meteor Crater.
Planetary Geology
Gene Shoemaker’s research marked the beginning of his work in a fledgling field: planetary geology, which later became a crucial branch of planetary science. Shoemaker went on to work closely with the Apollo program, creating a geologic map of the Moon and helping to train the astronauts who gathered moon rocks and did groundbreaking geological research that helped astronomers better understand the origins of the Moon itself.
Shoemaker himself had dreamed of being the first scientist to visit the Moon. Unfortunately, he was diagnosed with Addison’s disease in 1963, an illness that disqualified him from the astronaut corps.
However, he continued to campaign vigorously for the inclusion of a geologist among NASA’s lunar astronauts and succeeded when fellow Caltech-trained geologist Harrison “Jack” Schmitt visited and explored the Moon as a crew member of Apollo 17.
This article comes directly from content in the video series Great Heroes and Discoveries of Astronomy. Watch it now, on Wondrium.
Advancement in Planetary Science
Planetary science has experienced an immense evolution in the years since the Apollo program. We haven’t yet sent crewed missions to any other objects in the solar system, but we have capitalized on humanity’s spaceflight abilities to send missions all over the solar system, including many that have specifically focused on studying asteroids and comets.
The Galileo mission to Jupiter was the first to perform a close fly-by of two asteroids in the early 90s. The Stardust mission, launched in 1999, was a landmark achievement for planetary science. It flew close enough to a comet to actually collect samples of the dust grains pouring off of the comet’s surface before successfully returning to Earth, bringing the samples home for planetary geologists to study.
Similarly, the Hayabusa mission landed on an asteroid in 2005 and collected samples that were returned to Earth. More recently, the Rosetta mission flew to a comet, and in 2014 successfully dropped a lander onto its surface, marking the first-ever landing on the surface of a comet.
All of these missions were made possible by enormous teams of people working with NASA, the European Space Agency, the Japan Aerospace Exploration Agency, and others: the engineering, design, fabrication, launch, and operation of these kinds of missions is an immensely complicated process and one that can only be achieved with the dedication and hard work of hundreds of astronomical heroes.
Advancements in Planetary Science
For astronomers, who often study stars and galaxies that are millions or billions of light-years away, the idea of visiting the objects we study seems like the stuff of imagination. The fact that this is possible for moons, other planets, asteroids, and comets is a testament to the incredible scientific and technological advances that we’ve made in the field of planetary science.
Still, sometimes planetary scientists don’t have to go to quite that much effort. Sometimes—as in the case of the object that made Meteor Crater in Arizona—the objects come to us!
Common Questions about Understanding Planetary Science
About 35 miles east of Flagstaff, Arizona, is an enormous crater. Three-quarters of a mile across and 560 feet deep, its presence had fascinated geologists for decades. In 1960, most geologists believed that it had been caused by a volcanic explosion. However, others thought the crater had been caused by some kind of impact from space.
When Gene Shoemaker and his colleagues began studying the chemistry of the crater, they recognized minerals that could only have formed in the high temperatures and pressures of a tremendous impact. They reported that the crater had not been formed by a volcano. It had been formed by a meteor.
Gene Shoemaker worked closely with the Apollo program, creating a geologic map of the Moon and helping to train the astronauts who gathered moon rocks and did groundbreaking geological research that helped astronomers better understand the origins of the Moon itself.
