A visitor asks, "Why are the orbits of the planets elliptical?"
A) Because both the Sun and the other planets are pulling on each planet, which distorts a circular orbit into an ellipse. B) Because collisions between the planets that took place when the solar system was forming knocked the planets into orbits of this shape. C) This is the only shape that a planet's orbit can have; other types of objects like moons and stars can have orbits with different shapes.
D) This is the only shape an orbit can have that is stable so that the planet doesn't fall into the Sun or go shooting off into space.