Why Do the Planets Orbit in a Plane Parallel to the Spin Axis of the Sun?

-- | July 6, 2014

Question: Are orbits in our solar system really moving sideways around the sun instead of up and down around the sun? It’s a perspective/gravity/free-falling thing that’s hard for me to understand sideways. — Jay

Answer: First, let me answer a related question. Why do the planets all orbit the Sun in (nearly) the same plane? This “co-planar” orbital motion is due to the fact that during the formation of the Solar System from a cloud of collapsing gas and dust the Sun and planets settled into a disk structure. This disk structure is the result of the conservation of angular momentum which results when a spinning cloud of gas and dust collapses, and represents a balance point between gravitational collapse and the outward force due the spin of the disk (called centrifugal force). Now, this disk could have been in any orientation, but the most likely configuration would have the residual spin of the disk, including the planets, aligned with the residual orbital spin of the Sun. This is why the spin axis of the Sun is parallel to the spin axis of the rest of the solar system.

Jeff Mangum

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