The smaller and more distant of the two moons of Mars is Deimos. Deimos is 15 kilometers in its long dimension and 11 kilometers in its short dimension. The surface of Deimos is generally smoother than Phobos, possibly caused by a thicker layer of fragmental debris, or regolith, that fills in irregularities on its surface.
Mosaic of Viking Orbiter images 428B34 and 428B36. Image processing by Brian Fessler, Lunar and Planetary Institute