A year on Mars is the equivalent of 687 Earth days or almost two years on Earth. The length of a year is determined by the amount of time it takes for a planet to make one complete orbit around the sun.
Mars is approximately 142 million miles from the sun, compared to Earth's average distance of about 93 million miles. The average speed at which Mars orbits the sun, 14.5 miles per second, is also slower than the 18.5 miles per second at which the Earth makes its orbit. The average length of a day on Mars, 24 hours and 37 minutes, is 41 minutes longer than the length of an average Earth day.