Do the orbits of asteroids, comets and planets have a perihelion and an aphelion?
Planets, asteroids and comets are star-orbiters. The orbits are ellipses having a focus at the center of the parent star. So, the distance from the star attains mini/max - perihelion/aphelion.
The distortion of an ellipse from a circle is revealed by the parameter called eccentricity e that lies between 0 and 1. Mercury's orbit has highest e (nearly 0.21). Neptune and Venus have low e (near 0.01). Comets' e are on the higher side, and so, their orbits are called near-parabolic For parabola, e = 1. There is no (never to return) parabolic orbit..