New thermal imagery paints the Mars moon Phobos in a candy-colored light.
NASA's Mars Odyssey spacecraft, which has been orbiting the Red Planet since 2001, used its infrared camera to measure temperature variations on the 16-mile-wide (25 kilometers) Phobos at three different stages of illumination.
An image captured on Dec. 9 of last year shows Phobos in full sunlight, with a maximum measured temperature of 81 degrees Fahrenheit (27 degrees Celsius). A second shot, taken on Feb. 25 when the moon was in full eclipse, registered temperatures as low as minus 189 degrees F (minus 123 degrees C) — some of the lowest ever recorded on Phobos, Mars Odyssey team members said.
Related: Mars' moons: Facts about Phobos and Deimos
The third new image, taken on March 27 when Phobos was coming out of Mars' shadow, observed temperatures between those two extremes.
Lots of information about the moon can be gleaned from the thermal imagery, which NASA officials released Tuesday (June 9).
"We're seeing that the surface of Phobos is relatively uniform and made up of very fine-grained materials," Christopher Edwards of Northern Arizona University in Flagstaff, who leads the processing and analysis of the Phobos images, said in a statement.
"These observations are also helping to characterize the composition of Phobos," Edwards said. "Future observations will provide a more complete picture of the temperature extremes on the moon's surface."
A more complete picture could, in turn, help astronomers better understand the history of Phobos and Mars' other moon, the 8-mile-wide (13 km) Deimos. Some scientists think the satellites are captured asteroids, but others argue that they bothcoalesced from material blasted off the Red Planet's surface by powerful impacts.
Mars Odyssey's infrared camera is known as the Thermal Emission Imaging System, or THEMIS for short. The newly released infrared imagery does not show Phobos as it would look to the human eye.
"All of the THEMIS infrared images are colorized to show temperature variations and are overlain on THEMIS visible-light images taken at the same time to show the geology of the surface," NASA officials wrote in the same statement. "The one exception is the eclipse image, which is computer-generated and shows what Phobos would have looked like if it wasn't in complete shadow."
Mars Odyssey is primarily devoted to studying the Red Planet's surface. But the probe has also studied Phobos in recent years, a target switch that requires flipping the probe upside-down.
Though Odyssey remains in good health, it's unclear how much longer the orbiter will continue doing its work (which also includes relaying communications between mission control on Earth and robots on the Martian surface, such as NASA's rover Curiosity). The 2021 federal budget request allocates just $1 million to the project next year, a more than 90% cut that, if enacted, would effectively end the Odyssey mission.
- Mars Odyssey: Pictures from longest Mars mission
- Japan to launch a sample-return mission to Mars moon Phobos in 2024
- A brief history of Mars missions
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
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