Solar System: Mercury

"Mercury is one of the eight planets that orbit, or travel around, the sun in the solar system. It is the closest planet to the sun..."

"the innermost planet of the solar system and the eighth in size and mass. Its closeness to the Sun and its smallness make it the most elusive of the planets visible to the unaided eye..."

"Mercury—the smallest planet in our solar system and closest to the Sun—is only slightly larger than Earth's Moon..."