Astrogeology is the study of geology beyond Earth: the rocks, minerals, surface features, and internal processes of other planets, moons, asteroids, and comets. It applies the same principles geologists use to understand Earth (mapping terrain, analyzing rock samples, studying volcanism and erosion) to every solid body in the solar system. The field is sometimes called planetary geology, and it sits at the intersection of geology, physics, chemistry, and space exploration.
What Astrogeologists Actually Study
On Earth, geologists examine four major forces that shape landscapes: volcanism, tectonics, erosion, and impact cratering. Astrogeology looks at these same processes playing out under wildly different conditions. Mars has a volcano, Olympus Mons, that dwarfs anything on Earth. Europa and Enceladus, moons of Jupiter and Saturn respectively, have ice shells hiding liquid oceans underneath. Asteroids preserve rock chemistry that has gone essentially unchanged for billions of years. Each body offers a natural experiment that would be impossible to replicate in a lab.
The field also includes planetary cartography, the making of detailed maps of other worlds, and remote sensing, the use of spacecraft instruments to identify minerals and measure terrain from orbit. Visible and near-infrared spectrometers on orbiters and rovers can identify specific minerals on a planet’s surface from a distance. Laser altimeters build precise elevation maps. Gamma-ray and neutron detectors reveal what elements are present in the top layer of soil or rock. NASA’s Dawn spacecraft used exactly these tools to survey the asteroid Vesta and the dwarf planet Ceres between 2011 and 2018.
How the Field Began
Astrogeology as a formal discipline traces back to 1963, when the U.S. Geological Survey established the Astrogeology Science Center in Flagstaff, Arizona. Its original purpose was to map the Moon and help train Apollo astronauts to recognize and collect geologically useful samples on the lunar surface. Eugene Shoemaker, a geologist who had studied impact craters in the Arizona desert, was instrumental in founding the center and in making the case that space exploration needed trained geologists, not just engineers and pilots.
The USGS Astrogeology Science Center still operates today as a hub for planetary geoscience, cartography, and remote sensing. It also manages the planetary nomenclature system on behalf of the International Astronomical Union, the body responsible for officially naming features on other worlds.
How Planets and Moons Get Their Names
Every crater, mountain, and canyon on another world that receives an official name goes through the International Astronomical Union. The rules are surprisingly specific. Names must be simple, clear, and unambiguous. Features smaller than 100 meters generally don’t get named unless they have exceptional scientific interest. No names with political, military, or religious significance are allowed, except for political figures who lived before the 19th century. Anyone being honored by having a feature named after them must have been dead for at least three years. Each planetary body follows a naming theme, and those themes are expanded as new features are discovered. Wikipedia is explicitly not accepted as a source to support a proposed name.
Mars: A Case Study in Planetary Geology
Mars is the best-studied planet in astrogeology after Earth, and its geological history has been divided into three broad eras based on how many impact craters scar the surface. Older surfaces have more craters, younger surfaces fewer. The oldest era, the Noachian, stretches from the planet’s formation to roughly 3.5 to 3.8 billion years ago. Noachian surfaces are heavily cratered and show evidence of ancient water flow, including clay minerals that only form in the presence of liquid water.
The Hesperian era followed, lasting until somewhere between 3.55 and 1.8 billion years ago (the range reflects uncertainty about how frequently meteorites struck Mars over time). This was a period of massive volcanic eruptions that laid down extensive lava plains across the planet’s surface. The most recent era, the Amazonian, extends to the present day. It produced Olympus Mons, the enormous landslides in the Valles Marineris canyon system, and the polar sand dunes visible today. Amazonian surfaces have relatively few impact craters, suggesting the planet’s surface has been geologically active in more recent times.
Ice Volcanoes and Hidden Oceans
Some of the most exciting work in astrogeology involves icy moons that are geologically active in ways no one expected decades ago. Saturn’s moon Enceladus shoots high-speed jets of water ice from giant fissures near its south pole. These jets contain salts and organic compounds, strong evidence of a liquid ocean beneath the ice shell. A 2024 model published in the Journal of Geophysical Research proposes that these eruptions work much like opening a shaken soda can: dissolved gases in the ocean water expand as it rises through narrow conduits in the ice, driving the material upward and out into space. This mechanism is strikingly similar to certain types of explosive volcanism on Earth.
The practical implication is significant. Because the water doesn’t undergo much chemical change during its ascent from ocean to jet, samples collected from the plume (or from where it settles on the surface) would closely reflect the ocean’s actual composition. That makes Enceladus a prime target for missions searching for signs of life beyond Earth.
What Asteroid Samples Have Revealed
Astrogeology isn’t limited to studying surfaces from orbit. In 2023, NASA’s OSIRIS-REx mission returned a sample from the asteroid Bennu, and the results were remarkable. The sample contained 14 of the 20 amino acids that life on Earth uses to build proteins, plus all five nucleobases used in DNA and RNA. Scientists also found high concentrations of ammonia and formaldehyde, both important building blocks for biological chemistry.
Traces of 11 different minerals that form when salt water slowly evaporates were identified in the sample, including one called trona that had never been found in extraterrestrial material before. Perhaps most intriguing, the amino acids in the Bennu sample were an equal mix of left-handed and right-handed mirror-image forms. Life on Earth uses almost exclusively left-handed amino acids, so the equal mix in Bennu suggests these compounds formed through non-biological chemistry, preserving a snapshot of the raw ingredients available before life began.
Current and Upcoming Missions
NASA’s Artemis program represents the next major chapter in astrogeology. The Artemis III mission, which will land astronauts near the Moon’s south pole, has four primary geology goals: understanding how the Moon originally formed (including testing models of a global magma ocean that once covered its surface), pinning down the history of asteroid and comet impacts in the inner solar system, studying how the lunar surface weathers and changes without an atmosphere, and characterizing water ice and other volatile compounds trapped in permanently shadowed craters near the poles.
The top-priority objective is determining the age of the South Pole-Aitken Basin, one of the largest and oldest impact craters in the solar system. Dating this basin would anchor the entire timeline of bombardment that shaped the early Earth and Moon, a question that has remained unresolved for decades. Planning for the geology investigation is ongoing, with multiple potential landing sites still under consideration.
How to Work in Astrogeology
The typical path into astrogeology starts with a bachelor’s degree in geology, geophysics, or a related earth science, followed by graduate work focused on planetary topics. USGS qualification requirements for research geologist positions specify a four-year geology degree plus additional coursework in some combination of mathematics, physics, chemistry, planetary geology, geophysics, cartography, or computer science. For geophysics-focused roles, at least 30 semester hours of math and physical sciences are expected.
The major employers are NASA, the USGS Astrogeology Science Center, university research labs, and organizations like the Lunar and Planetary Institute. Day-to-day work varies widely. Some astrogeologists spend their time processing orbital imagery and building geologic maps of planetary surfaces. Others analyze returned samples in clean rooms. Some design instruments for future missions or develop computer models of volcanic eruptions on icy moons. Fieldwork on Earth, particularly at sites that resemble other planetary environments like lava fields in Iceland or dry valleys in Antarctica, remains an important part of the discipline.