Answer:
Mercury
Step-by-step explanation:
According to Kepler, Mercury is the planet that travel the fastest. Planets closer to the sun move faster compare to those farther from the sun.
Mercury is the closest to the sun and it travel the fastest. Mercury rotate around the sun in 88 days.
According to Kepler rule, the closer the orbit to the star, the quicker the orbit due to gravitational forces exerted upon the body by the star.