Mercury has the shortest orbital period of any planet in the solar system, completing a trip around the Sun every 88 days. It is the smallest of the eight planets, as well as the closest to the Sun.
The orbit of Mercury is highly eccentric; its distance from the Sun varies from 46 million to 70 million kilometers. Mercury was once thought to rotate at the same speed that it orbited the Sun, always showing the same side to the star. In 1965, astronomers at the Arecibo Observatory proved that the planet rotates. One rotation on Mercury is completed approximately every 59 days on Earth.