| Piú viste - Phobos: the "Doomed" Moon |
PHOBOS-Image013-411-20081008-5870-6-s12_nd-01-PhobosSeries_H1.jpgViews of Phobos55 visiteThis sequence of images was obtained by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express on 26 July 2008 (orbit 5861), at a distance of about 2295 Km from the moon’s centre, and provides a striking impression of the encounter.
These imagee was taken using all 9 imaging channels of the camera. The resolution shown here is 92 mt/pixel for each image.
HRSC is a so-called push-broom camera, building up images in a ‘scanning’ mode while the spacecraft passes over the surface. Its nine channels, or scanning lines, are oriented in different directions that spread from 18,9° behind the nadir viewpoint (corresponding to a vertical line of sight), to 18,9° ahead of the nadir. This gives the camera its stereo-viewing capacity.MareKromium
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PSP_007769_9015_IRB.jpgPhobos (Natural Colors; credits: NASA)54 visitePhobos, and the second Martian moon, Deimos, are interesting for several reasons. Both objects are small, with average diameters of just 22 and 12 Km, respectively.
At this size, their gravity is insufficient (less than 1/1000th of Earth) to pull them into spherical shapes, in contrast to the larger moons and planets in the Solar System.
Both moons are tidally locked to Mars, meaning, like our own moon relative to Earth, they present the same side to Mars all the time. The small size and composition (determined from spectroscopy) of Phobos and Deimos make them very similar to some asteroids.
Most asteroids are located in a belt between Mars and Jupiter, with others having orbits that cross that of Mars. Therefore, it is possible that Phobos and Deimos are captured asteroids.
Other hypotheses are that they formed with Mars in the early Solar System, or are composed of material blasted off of Mars by impacts.MareKromium
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PSP_007769_9015_MarsShine.jpgIn the Mars-Shine... (credits: NASA)54 visiteThis is a close-up and enhanced part of image PSP_007769_9015. In the original image, detail in the black, un-illuminated portion is not apparent. However, seen in enhanced detail here, craters are clearly visible.
This faint illumination is from reflected light off of Mars (“Marsshine”). This is directly analogous to “Earthshine,” where reflected sunlight from our planet illuminates the dark side of the Moon.
The ability to see features on Phobos illuminated by Marsshine demonstrates the high sensitivity of the HiRISE camera.MareKromium
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PSP_007769_9015_RED.jpgPhobos (RAW Frame; credits: NASA)54 visitenessun commentoMareKromium
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