Planetary Mapping

Why do maps matter in space exploration?

Maps are an important part of space exploration and do more than help people navigate. They allow scientists and astronauts to understand how the rocks at one location relate to or are different from rocks at other locations. Maps can also be used to identify important resources like ice, which could be used to create building materials, fuel, or drinking water for astronauts. Maps can also be used to identify hazards like boulders or steep cliffs, that may make it unsafe for a rover to land, or for an astronaut to travel through an area. Using maps to identify safe, efficient, and scientifically useful routes for astronauts is called traverse planning.

How are planetary maps different?

Planetary geologic maps are very similar to Earth-based geologic maps, but with one important difference: On Earth, mappers can use field-based observation as well as images taken from planes and orbiting spacecrafts. With a few exceptions for locations with rovers, landers, or crewed surface missions, planetary geologic mappers are not able to observe their map area up close and in person and have only images taken by orbiting spacecraft. This means they interpret and describe things differently than geologic maps of Earth. For example, terrestrial (Earth-based) geologic mappers commonly divide units by lithology (rock type) or grain size (for example, sand or gravel). Planetary geologic mappers often do not have detailed enough information to know what type of rock or grain size is present, and instead must divide the planet’s surface into geologic units using differences in tone (how bright or dark a material is), color, context, composition, and surface texture (at multiple scales). Units can be made of different rock types or be variations of the same rock type. The process of identifying geologic units and their characteristics helps scientists better understand the complex surfaces they study. 

Learn more about some of our recently-published geologic maps:

How can you map if you can't go there?

Because they can’t physically visit their study locations, planetary scientists and mappers use many kinds of data from different spacecraft and instruments. This allows them to understand the rocks in a variety of ways, not just how they look to the naked eye. In addition to the cameras most people are familiar with, missions carry instruments that collect images using infrared and ultraviolet light, which are outside the range that is visible to the human eye. These images measure the amount of reflected or emitted light at many different wavelengths, can reveal what minerals and chemicals are present much like the fingerprint of a rock. Infrared data can measure how quickly a unit heats up and cools off during the day-night cycle (thermal inertia), which can be used to estimate how solid a material is: solid rocks heat up and cool down slowly, while loose materials like sand heat and cool rapidly.

How can we tell how a rock formed on another planetary body?

During the mapping process, scientists develop interpretations for each unit. These interpretations suggest how each unit formed, through impacts, volcanism, or sedimentary processes. Geological interpretations are often based on observations of geological processes made here on Earth and experiments conducted in laboratories. However, many geologic properties that can be observed during planetary mapping can be caused by more than one process, so it is very important for mappers to keep their interpretations separate from their observations. 

How do we name features on other planetary bodies?

Planetary scientists name features so they have easy and consistent names to use when talking about locations. It's much simpler to say "Jezero crater" than trying to describe one specific crater on a planetary surface. Features on other planetary bodies get named just like mountains and rivers on Earth, and each planetary body has a theme for names. Each type of feature on that body (like craters) has an even more specific theme. For example, features on Venus are all named after women: dorsa (long ridges) are all named after sky goddesses, plana (plains) are named after goddesses of prosperity, and large craters are named after women who have made outstanding contributions to their field.

Anyone can propose a name for a planetary feature. Names must fit the category for that feature and planetary body, and proposers must explain why the feature should be named. The International Astronomical Union reviews proposed names, and if they are accepted, they become official. Learn more about names across the solar system at the Gazetteer of Planetary Nomenclature.