As of March 2020, our Mars Odyssey spacecraft has captured these six views of the Martian moon Phobos. The orbiter’s infrared camera, the Thermal Emission Imaging System (THEMIS), is used to measure temperature variations that provide insight into the physical properties and composition of the moon.
Chronologically, the views represent waxing, waning and full phases of the moon. On Feb. 25, 2020, Phobos was observed during a lunar eclipse, where Mars’ shadow completely blocked sunlight from reaching the moon’s surface. This provided some of the coldest temperatures measured on Phobos to date: The coldest measured was about -189 degrees Fahrenheit (-123 degrees Celsius). On March 27, 2020, Phobos was observed exiting an eclipse, when the surface was still warming up.
All of the THEMIS infrared images are colorized and overlain on THEMIS visible images taken at the same time, except for the eclipse image, which is overlain on a computer-generated visible image of what Phobos would have looked like if it wasn’t in complete shadow. Phobos is about 15 miles (about 25 kilometers) across.
Image Credit: NASA/JPL-Caltech/ASU/NAU