Bruce Murray Space Image LibraryOne of the first spacecraft photos of Phobos, from Mariner 7 One of the first spacecraft photos of Phobos, from Mariner 7 The small, dark spot near the top of this photo is Phobos. Phobos covers about 40 picture elements. From this data, Phobos was found to be an oval object approximately 22.5 kilometers long and 17.5 kilometers wide. Also, it was concluded that Phobos is a very dark object, with an albedo of 6.5%. NASA / JPL / Piotr MasekFrame 7F91.