A planetary geologist studies the geology of planets other than Earth as well as their satellites. The field, also known as astrogeology or exogeology, is closely related to traditional geology but focuses on topics like a planet’s internal structure and volcanic and surface activity. A planetary geologist may examine samples retrieved from space missions or meteors that crash into the Earth’s surface. Photographs and other data about comets, moons, and planets sent from probes are also of interest to the planetary geologist. Producing accurate planetary and lunar maps and making inferences about the possibility of life on other planets are two of many planetary geologist research goals.
Celestial bodies like planets, moons, and comets all have geological features that are scientifically significant. For example, the tallest mountain in the solar system is on Mars, and there are pockets of frozen ice in craters on Mercury. Data about these features are gathered in many ways, including via telescope, samples collected by astronauts, and photos and data from space probes. Careful mapping and investigation of these geological features can reveal much about how a body was formed, how its geological composition compares to Earth’s, and whether there was or can be life there.
A planetary geologist uses techniques from other fields within geology, like geochemistry and geophysics, to study the composition and structure of the geological features and composition of other planets and their satellites. Physical analysis of samples and data and photographs are the primary sources of information. This research can reveal why a planet is a certain color, whether there is or was water, and if there is any volcanic activity on the surface. For example, Mars is red because the planet’s surface is covered with iron oxide that is also carried into the atmosphere.
An important task for a planetary geologist is to map the surface of a planet or one of its satellites. Space probes send back high-definition photographs of the surface that reveal craters and other features like mountains and valleys as well as color and texture. Orbital high-resolution photographs can be combined with 3-D modeling to enhance the surface image and reveal even minute details. Evidence of streaks running down into a crater’s slops during spring and summer on Mars can help a planetary geologist make inferences about the presence of liquid rather than just frozen water. Liquid water provides a better environment for life than water in a frozen state.
In addition to mapping, a planetary geologist may also focus on impact cratering and planetary atmospheres. Impact cratering is a primary geologic process that shapes planetary surfaces and can form many geological features. A geologist must distinguish between cratering caused by volcanic activity and that caused by the impact of a foreign body. Planetary atmospheres can reveal much about differences in gravitational forces but also shape planetary surfaces via wind, frost, and precipitation.
A career as a planetary geologist requires a doctoral degree in the subject. As this is a niche profession within geology, only a small number of institutions offer advanced degrees in this area. The majority of planetary geologists in the United States are employed by universities, the Unites States Geology Survey Astrogeology Science Center, and the National Aeronautics and Space Administration. They conduct research and create planetary and lunar maps that emphasize everything from evidence of past water concentrations to impact craters and volcanic activity.