Question

which characteristic do mercury and mars share?
many moons
rocky surfaces
thick atmospheres
moderate temperature fluctuations

Explanation:

Mercury has no moons, while Mars has two small moons. Mercury has a very thin atmosphere, and Mars has a thin atmosphere too (not thick). Mercury has extreme temperature fluctuations (from very hot to very cold), while Mars has more moderate but still significant temperature changes. Both Mercury and Mars are terrestrial planets with rocky surfaces.

Answer:

rocky surfaces