Since Odyssey began orbiting the Red Planet in 2001, THEMIS has provided compositional and thermal-properties information from all over Mars, but never before imaged either Martian moon. 29, 2017, with the Thermal Emission Imaging System (THEMIS) camera on NASA's Mars Odyssey orbiter. Compositional information from THEMIS might help pin down their origin.Ĭolors in this image of the Martian moon Phobos indicate a range of surface temperatures detected by observing the moon on Sept. One major question about Phobos and Mars' even smaller moon, Deimos, is whether they are captured asteroids or bits of Mars knocked into the sky by impacts. Observations in multiple bands of thermal-infrared wavelengths can yield information about the mineral composition of the surface, as well as the surface texture. Cameras on other Mars orbiters have previously taken higher-resolution images of Phobos, but none with the infrared information available from THEMIS. Phobos has an oblong shape with an average diameter of about 14 miles (22 kilometers). If it heats up very quickly, it's likely not very rocky but dusty instead." "As you go from predawn area to morning area you get to watch the heating behavior. "Including a predawn area in the observation is useful because all the heating from the previous day's sunshine has reached its minimum there," Hamilton said. As barefoot beach walks can confirm, sand warms or cools quicker than rocks or pavement. This provides information about how quickly the ground warms, which is related to the texture of the surface. Looking across the image from left to right presents a sequence of times of day on the Martian moon, from before dawn, to sunrise, to increasing amounts of time after dawn. "Part of the observed face of Phobos was in pre-dawn darkness, part in morning daylight," said THEMIS Deputy Principal Investigator Victoria Hamilton of the Southwest Research Institute, headquartered in San Antonio. The apparent motion is due to progression of the camera's pointing during 18 seconds of observing, not from motion of Phobos. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.This series of images was taken in visible-wavelength light as the THEMIS camera on NASA's Mars Odyssey scanned across the Martian moon Phobos on Sept. The Thermal Emission Spectrometer is operated by Arizona State University and was built by Raytheon Santa Barbara Remote Sensing. MSSS operates the camera from its facilities in San Diego, CA. and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. Previous images from the Viking spacecraft in the 1970's were not of sufficient resolution to show the effectiveness of gravity on Phobos in moving material down slopes. The motion of debris down slopes is guided by gravity, which is only about 1/1000th that of the Earth - e.g., a 68-kilogram (150- pound) person would weigh only about 57 grams (2 ounces) on Phobos. The presence of material of different brightness on the far crater slopes and in some of the grooves shows that the satellite is heterogeneous (that is, it is made of a mixture of different types of materials). The far wall of the crater shows lighter and darker streaks going down the slopes (C). This crater is nearly half the size of Phobos and these grooves may be fractures caused by its formation. Also crossing at and near the rim of Stickney are shallow, elongated depressions called grooves. Some of these boulders are enormous - more than 50 meters (160 feet) across. Individual boulders are visible on the near rim of the crater (D), and are presumed to be ejecta blocks from the impact that formed Stickney. This is the largest crater on Phobos, Stickney, 10 kilometers (6 miles) in diameter. The image shows several new features of this lumpy moon - features that are associated with the prominent crater seen in the upper left quarter of the image. This image is one of the highest resolution images (4 meters or 13 feet per picture element or pixel) ever obtained of the Martian satellite. Phobos was observed by both the Mars Orbiter Camera (MOC) and Thermal Emission Spectrometer (TES). The minimum distance between the spacecraft and Phobos was 1,080 kilometers (671 miles). This image of Phobos, the inner and larger of the two moons of Mars, was taken by the Mars Global Surveyor on August 19, 1998.
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