Multiple choice general knowledge science & technology Mercury orbits the sun once in every _____ days 87 87.5 88 87.969 Reveal answer Fill a bubble to check yourself D Correct answer Explanation Mercury completes one orbit around the Sun in approximately 88 Earth days. The precise value is about 87.969 Earth days. This is the shortest orbital period of any planet in our solar system, which is why Mercury is the fastest-moving planet.