What is Exo-cartography? Mapping the Climate and Surface of Exoplanets

Elizabeth Borneman


Exo-cartography or extrasolar cartography is the science of mapping planets that are outside of Earth’s solar system. Exo-cartographers have to be a combination of photographer, mathematician and rocket scientist in order to create an accurate description of these planets, many of which are tens of thousands of light years away from Earth.

Mapping Exo-solar Planets

Exo-cartographers map exo-solar planets, or planets that are in orbit around another star aside from Earth’s sun. The brightness of these other stars and the distance between us and their orbiting exoplanets render our telescopes unable to photograph many of these planets, so exo-cartographers have had to come up with unique ways to get a picture of these planets without the use of traditional imaging devices.

Exo-cartographers create maps of exoplanets using complex equations that allow them to map the brightness of the star the planets are orbiting around. When the planet orbits behind and in front of the star (an eclipse) exo-cartographers can measure the changes in the brightness of the star to determine how fast the planet is moving, how quick or slow its planetary year is (the time it takes to orbit once around its star), and its size. With this rudimentary rendering of the exoplanet in question exo-cartographers can begin mapping things like temperature, cloud cover, weather patterns and even the existence of continents and water forms on the planet’s surface.

Creating a Temperature Map of Exoplanets

The colors that appear in temperature maps of exoplanets are essential in helping to determine the qualities that make this planet unique. Exo-cartographers create a temperature map of the day side of the planet based on readings they acquire during the planet’s eclipse of its star; the temperature image of the night side of the planet takes a bit more time, as data must be collected during the entire planetary year as it completes an orbit around the star. Depending on the speed of the planet, this could take a very long time!

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Temperature readings from an exoplanet can tell us how hot it is on average, where the wind is blowing, how much cloud cover it has and what materials likely make up its atmosphere. Major geographic features can also be mapped using this technique. This strategy, called ‘rotational unmixing,’ was created by Nick Cowen, who works at Northwestern University in Illinois. His analyzing of the different color hues that can be found on exoplanets to show features from geography to weather have revolutionized the way exo-cartographers look at and ultimately create a picture of planets too far away for us to see clearly. This method uses heat sensors to determine the temperature of an exoplanet and reflectivity of light to map clouds, ice, water and any landmasses that might be present on the exoplanet.

Further study has shown that while Cowen’s theory works well on planets with distinctive features, planets with lesser contrast between water, landforms and clouds don’t work so well. Others have found that distinguishing between clouds and ice can be difficult using the temperature spectrum as a guide.

This EPOXI mission image shows what an Earth-like exoplanet might look like from afar. Image credit: NASA/JPL-Caltech/UMD/GSFC
This EPOXI mission image shows what an Earth-like exoplanet might look like from afar. Image credit: NASA/JPL-Caltech/UMD/GSFC

The Role of Exo-cartographers

Exo-cartographers play an important role in mapping the universe outside from the solar system we live in. Although long-distance space travel is currently impossible (to the extent of getting to some of the nearest exoplanets is concerned) there may come a day when we can build a telescope big enough to take pictures of some of these planets, and an even farther future day when one of them might prove to be habitable. In the meantime by observing the planets outside of our solar system we can not only continue to learn more about the universe around us, but we can also find some truths about the planet we live on as well.

How Studying Exoplanets Helps Researchers Understand Life on Earth

Nick Cowen discussed the idea of looking to other planets to solve some of the mysteries of life that our planet has not divulged the answers to quite yet. His interest lies in the effects clouds have on the greenhouse effect- a problem that many are searching for the answer to as global warming becomes an increasing threat to different aspects of life on Earth. While we can determine with reliability the effects on Earth’s temperature that CO2, vapor and ice have on the temperature of Earth, the unknown factor of clouds remains elusive. Do they add to the greenhouse effect or reflect some of the sun’s heat?

The answers might be found by studying the clouds on exoplanets. This is a smaller way in which exoplanets might help us mitigate the human effects of life on Earth while also giving us the chance to explore the possibilities of life on other planets outside our solar system.

We might not be headed on any manned missions to the ends of space yet, but the day might come when we can take a clear picture of planets outside our solar system that could sustain life, or at least give us some knowledge about our own beautiful blue planet thanks to exo-cartographers around the world.


Cooper, Keith. Mapping New Worlds. Astronomy Now. 10 September 2010. http://www.astronomynow.com/news/n1009/10map/

Cowen, Nick. Chicago Ideas Week. Scientific Breakthroughs: Infinite Possibilities. 13 October 2014. https://www.chicagoideas.com/videos/437

Than, Ker. Mapping Distant Planet Surfaces Possible. Inside Science. 29 January 2013. http://www.insidescience.org/content/mapping-distant-planet-surfaces-possible/922


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About the author
Elizabeth Borneman
My name is Elizabeth Borneman and I am a freelance writer, reader, and coffee drinker. I live on a small island in Alaska, which gives me plenty of time to fish, hike, kayak, and be inspired by nature. I enjoy writing about the natural world and find lots of ways to flex my creative muscles on the beach, in the forest, or down at the local coffee shop.