Why are the planets found near the ecliptic?
The ecliptic is defined by the
of the Earth’s orbit
If the other planets are always found near the ecliptic, they must always be
located near the plane of the Earth’s orbit – at most slightly above or below it.
The planes of their orbits around the sun must almost match the Earth’s
Their slight motions above and below the ecliptic means the match isn’t
(Their orbits are slightly tilted relative to ours.)
From our text:
Horizons, by Seeds