The orbits of the planets all lie in nearly the same plane for preservation of angular momentum.
Ellipses
One of the discoveries that led to the modern view of the Solar System was that the "orbits" of the planets were ellipses.
Gravity holds the planets in their orbit
The planetary orbits of our solar system are considered "elliptical." This includes "circular" orbits, as a circle is a type of ellipse. In astrodynamics, an elliptical orbit and a circular orbit both fit into the description of a Kepler Orbit.
orbits of the planets.
Ellipses
One of the discoveries that led to the modern view of the Solar System was that the "orbits" of the planets were ellipses.
Venus has the least eccentric (most nearly circular) orbit of the eight in our solar system.
Gravity from the Sun holds the planets in their orbits.
The wording of this question needs to be improved to understand what you mean.
The gravity of the Sun keeps the planets in their orbits. They stay in their orbits because there is no other force in the Solar System which can stop them.
None of the planets pass out of our solar system. The orbits of the planets, irregular as they may be IS the solar system.
That was the work of Kepler, resulting in his Laws of Planetary Motion.
Gravity holds the planets in their orbit
All planets in our solar system have elliptical orbits.
It doesn't. All of the planets in our solar system orbits the sun.
Yes, none of the planets in our solar system have exactly circular orbits, though some are more eccentric than others.