Neptune has the largest orbit and the slowest orbital velocity. Neptune is the most distant planet from the sun and travels around it at 12,146 miles per hour. It takes almost 165 Earth years for Neptune to complete a single orbit.
Neptune was first discovered in 1846, and is the smallest of the gas giants found in the outer Solar System. Pluto was declassified as a dwarf planet in 2006, making Neptune the most distant planet. A scientific principle known as Kepler's Law, states that orbital velocity is slower for planets that are located at a greater distance from the Sun.