This sequence of 19 images was taken in visible-wavelength light as the Thermal Emission Imaging System (THEMIS) camera on NASA's Mars Odyssey orbiter scanned across the Martian moon Phobos. THEMIS also recorded thermal-infrared imagery during the same scan.
The apparent motion is due to progression of the camera's pointing during the 18-second span of the Sept. 29, 2017, observation, not from motion of Phobos. Timing is sped up by a factor of two in this animation. This was the first observation of Phobos by Mars Odyssey. Researchers have been using THEMIS to examine Mars since early 2002, but the maneuver turning the orbiter around to point the camera at Phobos was developed only recently.
Phobos has an oblong shape with average diameter of about 14 miles (22 kilometers). The left edge of the small moon was in darkness at the time, and the right edge in morning sunlight. The distance to Phobos from Odyssey during the observation was about 3,424 miles (5,511 kilometers).
THEMIS was developed by and is operated by a team based at Arizona State University, Tempe. NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Mars Odyssey mission for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, built the orbiter and partners in its operation. JPL is a division of Caltech in Pasadena.