Which planet travels round the sun at the highest and at the lowest speed?

Answer 1

According to Kepler's Third Law, the planets that are nearer to the Sun move

faster than the planets that are farther away. The closest planet - and thus the

fastest - is Mercury; the farthest planet from the Sun is Neptune.

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The way gravity works guarantees, that the closer an object is to the sun, the faster it moves, whether the orbit is almost circular or highly eccentric. This simple

rule instantly lines up the speeds of the various solar system objects for us:

Fastest speed:

Comets which, at their closest approach, spend part of their time inside the orbit of Mercury.

Their speed is highest when they're closest to the sun.

Known planet with the highest average speed:

The planet nearest the sun . . . Mercury.

Known planet with the lowest average speed:

The planet farthest from the sun . . . Neptune.

Known dwarf-planet-like objects with the lowest average speed:

Known objects farthest from the sun . . . Pluto, Eris.

Answer 2

• Low: Mercury.
• High: Jupiter.