Comets and Their Origins

Study Notes

Comets are remnants of planet formation, approximately 4.6 billion years old.
Unlike asteroids, which are mainly rock and metal, comets resemble "dirty snowballs".
They consist of frozen gases (carbon dioxide, methane, ammonia), water ice, and embedded dust and rocky material.
As comets approach the Sun, solar radiation vaporizes the icy surface, creating a gaseous coma and a visible tail.
The tail always points away from the Sun, often appearing to trail behind but sometimes alongside or in front of the comet.

Comets originate primarily from the Kuiper Belt and the Oort Cloud.
The Kuiper Belt is a disk of icy bodies extending from Neptune's orbit to about 50 AU from the Sun.
The Oort Cloud is at the edge of the Sun's gravitational influence, encompassing a spherical cloud of icy bodies.
Short-period comets (orbiting the Sun in 200 years or less) usually originate from the Kuiper Belt.
Long-period comets take hundreds or thousands of years to orbit the Sun and originate from the Oort Cloud.

Comets have a nucleus, coma, and tails.
The nucleus is a relatively small, solid, stable part composed of ice, gas, and a little dust.
The coma is a dense cloud of water, carbon dioxide, and other gases that sublimate from the nucleus.
The dust tail is composed of dust particles ejected from the nucleus, typically up to 10 million km long.
The ion tail is composed of plasma, and several hundred million km long, laced with rays caused by interactions with the solar wind

Asteroids are rocky and metallic objects that orbit the Sun.
They are also referred to as minor planets.
Asteroids are leftovers from the formation of the Solar System.
They are primarily located in the asteroid belt, which exists between Mars and Jupiter.
Ceres is the largest asteroid.

A meteoroid is a small, solid particle that orbits the Sun.
A meteor is a meteoroid that burns up in Earth's atmosphere.
A meteorite is a meteoroid that survives its passage through the atmosphere and lands on Earth's surface.
Meteor showers occur when Earth passes through a trail of debris left by a comet.

The Oort cloud is an enormous, spherical cloud encompassing our planetary system.
It extends approximately two to three light-years from the Sun.
This distance is considered the edge of the Sun's gravitational influence.

The Kuiper Belt is a region in the Solar System beyond the orbits of the eight major planets.
It stretches from 30 AU to approximately 50 AU from the Sun.
This region is similar to the asteroid belt; it contains many small, icy bodies, remnants of the Solar System's formation.
It is significantly larger and more massive than the asteroid belt.