Phobos: Preliminary Results from Mariner 7

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Science  15 May 1970:
Vol. 168, Issue 3933, pp. 828-830
DOI: 10.1126/science.168.3933.828


Analysis of an image of Phobos on Mariner 7 frame 7F91 indicates that the martian satellite is larger and has a darker surface than had previously been thought. The limb profile measures 18 by 22 kilometers and is elongated along the orbital plane. Phobos has an average visual geometric albedo of 0.065 lower than that known for any other body in the solar system. It seems probable that Phobos did not form by accretion around primordial Mars, but was captured at some later time.

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