Mars Odyssey orbiter takes first image of tiny moon Phobos
First ever infrared photos shed light on small moon's composition.

By Laurel Kornfeld | Jul 28, 2017

NASA's Mars Odyssey spacecraft has been orbiting the Red Planet since 2001, but it did not have the technological capability of imaging its tiny moon Phobos until now.

Its first images of the small moon were captured on September 29 using Odyssey's Thermal Emission Imaging System (THEMIS), which has been studying the Martian surface for the past 16 years in both infrared and visible light.

THEMIS' photos have helped scientists understand the composition of Mars' surface.

Key to its new ability to image Mars' small moons Phobos and Deimos is the fact that mission controllers can now rotate Odyssey to positions from which it can view the moons, noted Mars Odyssey project scientist Jeffrey Plaut.

In 2014, the mission team drew up procedures for rotating THEMIS to look up and image a passing comet. Prior to that, it had only looked down to the planet's surface.

"There is heightened interest in Phobos because of the possibility that future astronauts could perhaps use it as an outpost for missions to Mars," he said.

The first images of Phobos ever taken in the infrared, THEMIS' photos enable scientists to observe temperature changes across the small moon's surface, especially during sunrise and sunset.

When the September photo was taken, "Part of the observed face of Phobos was in pre-dawn darkness, part in morning daylight," noted THEMIS Deputy Principal Investigator Victoria Hamilton.

Observing heat patterns at sunrise allows scientists to learn the rate at which Phobos' surface warms.

"Including a pre-dawn area in the observation is useful because all the heating from the previous day's sunshine has reached its minimum there. As you go from pre-dawn 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," Hamilton explained.

Scientists are uncertain as to whether the oblong-shaped moon, which has a diameter of approximately 14 miles (22 km), and its smaller companion Deimos, are captured asteroids from the belt between Mars and Jupiter or parts of Mars itself dislodged by asteroid impacts.

Covered in powdery dust, Phobos appears to be a gravitationally held together rubble pile rather than solid rock. It is believed to be composed of carbonaceous chondrites, much like solar system asteroids.

Using thermal imagery will assist scientists in determining the moon's mineral composition and surface texture.


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