Mercury is the closest planet to the sun and has a shorter orbit than Earth. It rotates much slower, however, with each day lasting the equivalent to 58.65 Earth days.
The average distance to the sun is about 36 million miles, but this distance varies. Sometimes Mercury gets as close as 28 million miles from the sun while at other times it is 43 million miles away. This means that the orbit speed varies, depending on how close to the sun the planet is. Just before Mercury reaches its maximum orbit speed, that speed and its rotational speed become aligned. This gives the appearance of a static sun. Then, for a period of 8 days, Mercury orbits faster than it rotates. This makes it look as though the sun is going backwards in the sky.
Mercury's year is the shortest of all the planets in the solar system. Earth's is 365 days, while on Mars a year takes 687 Earth days. Neptune has the longest year. It takes more than 164 Earth years to orbit the sun.Learn more about Planets