5.43 km per second.
It is the orbital velocity (speed and direction) or orbital speed (rate of motion). It is usually stated as "average orbital speed" but is actually "mean orbital speed."
Of the major planets, Neptune. The speed of planets in their orbits is directly related to their distance from the sun. The farther a planet is from the Sun, the slower its orbital speed.
Orbital velocity refers to the speed at which a planet travels in its orbit.
If you still consider Pluto to be a planet then Pluto would be the slowest to orbit the sun. If you don't believe Pluto is a planet anymore then Neptune would be the slowest planet to orbit our sun.
The orbital speed of a planet is a direct result of the gravitational force between that planet and the Sun. The greater the force, the faster the speed.
According to http://solarsystem.nasa.gov/planets/, Venus has an orbital velocity of 78,341 mph, and Neptune's is 12,253 mph...
The orbital speed of a planet is the time it takes to cycle around the sun. The spinning speed of a planet is the time it takes for the planet to rotate on it's axis.
Venus is the slowest planet with a rotational speed of 243 Earth days equaling one Venusian day.
average orbital speed of 9.69km/s
Neptune spins at a equatorial rate of 2.68 km/sec, or a velocity of 9,660 km/hr (6000 mph).
The planet with the fastest wind speed is Neptune, with a speed of 2000 km/h (1,242.742 miles/h).
Neptune