While a lot of attention has been focused on Mars thanks to the rovers that are heading out there in 2020, the Red Planet's tiny moon Phobos has been relatively overlooked. Recently, though, NASA turned the THEMIS camera on its Mars Odyssey orbiter toward the moon to see what a day looks like in infrared wavelengths.
The Odyssey completed 60,000 orbits of Mars in 2015 and is still going strong, having earned the distinction of being NASA's longest-lived mission to the Red Planet. While it has provided NASA with lots of images, compositional and thermal information about Mars since it started orbiting the planet in 2001, it has never before been pointed at one of its moons. That changed on September 29, when the THEMIS camera was turned toward Phobos, a moon with an oblong shape having a roughly 14-mile (22-km) diameter.
THEMIS, which stands for Thermal Imaging System, is a camera that shoots in five visual image bands and 10 infrared bands. By combining images from both of these capabilities, researchers at NASA's Jet Propulsion Lab were able to create the image below, color-coded to show the surface temperatures of the moon. The image shows the progression of the heat on Phobos throughout a day with the left side still cloaked in pre-dawn darkness and the right side showing the part of the moon that had been exposed to the sun the longest.
"Including a predawn area in the observation is useful because all the heating from the previous day's sunshine has reached its minimum there," said said THEMIS Deputy Principal Investigator Victoria Hamilton of the Southwest Research Institute. "As you go from predawn area to morning area you get to watch the heating behavior. If it heats up very quickly, it's likely not very rocky but dusty instead."
Paving the way for the new Phobos observation, which took place on September 29, was an undertaking in 2014 in which the THEMIS team, JPL scientists and the spacecraft team at Lockheed Martin Space Systems figured out how to rotate the obiter to observe a passing comet. That procedure was adopted for the new Phobos photos.
NASA says that the image can help bring a greater understanding of how quickly the surface of Phobos cools and heats up, which can in turn provide information about the moon's texture and composition. "As barefoot beach walks can confirm, sand warms or cools quicker than rocks or pavement," says the space agency.
While Odyssey is only about 250 miles (400 km) from the surface of Mars, Phobos orbits about 3,700 miles (6,000 km) above the planet, which accounts for the relatively small size of the image.
Gaining a greater understanding of Phobos is important, because the moon may act as a pit stop for future missions to Mars, or could even hold permanent infrastructure critical to building colonies on the Red Planet. The images can also help scientists figure out whether Phobos is a captured asteroid or a chunk of Mars that got knocked loose and fell into orbit. Either way, speed is of the essence (not really), because researchers predict that Phobos will one day get torn apart by Mars and could form a ring around the Red Planet.