Why comets have elliptical orbits

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Groups Why Join? Astronomy Day. The Complete Star Atlas. Comets actually have a wide variety of orbital shapes — and they're not all extremely eccentric. Comets with very eccentric elliptical orbits arrive in the inner solar system from the Oort Cloud — a region thousands of astronomical units AU, the Earth-Sun distance away. If it weren't for gravitational perturbations, which are usually a result of coming too close to Jupiter, these comets would return to the Oort Cloud on the same orbit.

Both of these forces cause the eccentricity of the comet's orbit to become either smaller or larger; the latter case sometimes results in the comet completely escaping from our solar system. Other comets have less-elongated orbits. The Oort Cloud It is thought that most comets originate in a vast cloud of ice and dust that surrounds the solar system. The Oort Cloud, as it is called, extends several thousand times farther from the Sun than Pluto, the outermost planet.

A star passing near the solar system may have disturbed the motions of some comets in the Oort Cloud, sending them into the solar system.

Results from the Stardust mission indicate that some comet materials originated at very high temperatures, suggesting they formed near the Sun and were later transported to colder regions.

That is why the dust tail is usually curved rather than straight, and does not point directly away from the Sun, because it is also influenced by the motion of the comet.

The tails of the comet can be extremely large and my extend a distance of up to 1 AU the distance between the Earth and the Sun! The Kuiper belt is a region between about 30 and 50 AU from the Sun in the plane of the ecliptic. It is believed to be where most of the trans-Neptunian objects are, including Pluto and several other recently discovered dwarf planets.

It is also thought to be the origin of many of the solar system's short-period comets. There are several types of Kuiper belt objects, or KBOs. They probably moved into these irregular orbits as a result of gravitational interactions with gas giants, especially Neptune.

They are thought to be one source of short period comets. Many are in orbital resonance with Neptune, while others are in , or These orbital resonances are relatively stable orbits, and prevent the objects being pushed out of orbit by Neptune's gravity.

KBOs in a resonance are called plutinos , named after Pluto. The Oort cloud has never been observed but is thought to be a spherical distribution of icy objects like comets orbiting our Sun at distances between and , AU.