Figure 7-43 Phobos and Deimos (a) Phobos, the larger of Mars’s two moons, is potato-shaped and measures approximately 28 × 23 × 20 km. It is dominated by crater Stickney (on the right of the image), named for discoverer Asaph Hall’s wife (Angeline Stickney). (b) Deimos is less cratered than Phobos and measures roughly 16 × 12 × 10 km.