Why do comets orbit the Sun in an elliptical path?
All objects orbiting the Sun travel on approximately elliptical paths because of the laws of gravitational motion. For example, Earth’s orbit is elliptical, but not as elliptical as cometary orbits.
Many objects in the outer reaches of the Solar System – beyond Jupiter’s orbit – are icy and small. Some, which travel on paths which are mildly elliptical, remain cold and water-rich. Others, which are on highly elliptical paths and pass close to the Sun, produce tails of gas and dust. These tails define comets. Comets must travel on highly elliptical orbits just to reach close to the Sun. But there is a twist. In 2019, a potentially comet-like object named Borisov from outside of our Solar System passed through and close to the Sun, and is now on its way out on a hyperbolic path.
This interloper never orbited the Sun on an elliptical path, but appears to be icy like typical comets. As a result, Borisov might force us to rethink our naming of and assumptions about comets.