Phobos as observed by MAVEN’s Imaging Ultraviolet Spectrograph in December 2015. Orange shows mid-ultraviolet (MUV) sunlight reflected from the surface of Phobos, exposing the moon’s irregular shape and many craters. Blue shows far ultraviolet light detected at 121.6 nm, which is scattered off of hydrogen gas in the extended upper atmosphere of Mars. Phobos, observed here at a range of 300 kilometers, blocks this light, eclipsing the ultraviolet sky. On the day side of Phobos, some bright blue pixels indicate that the moon is reflecting far-UV light, which will allow for the first time a measurement of Phobos’ reflectivity at this wavelength, adding to an extremely limited database of measured far-UV reflectivity of small bodies in the solar system.
This image is in the public domain.
Original image data dated on or about December 1, 2015