Chapter 12

Oort Cloud

A huge, spherical region centered on the Sun, extending perhaps halfway to the nearest stars, in which trillions of comets orbit the Sun with random inclinations, orbital directions, and eccentricities.

Meteor Shower

A period during which many more meteors than usual can be seen.

Collisions not only bring meteorites and leave impact craters but also can profoundly affect life on Earth

An impact probably was responsible for wiping out the dinosaurs, and future impacts pose a threat that we cannot ignore

What are comets like

Comets are icy leftovers from the era of planet formation, and most orbit far from the sun. If a comet approaches the sun, its nucleus heats up and its ice vaporizes into gas. The escaping gases carry along some dust, forming a coma and two tails; a plasma tail and a dust tail. Larger particles can also escape, becoming the particle that cause meteor showers on Earth

Where do comets come from

Comets come from two reservoirs; the Kuiper belt and the Oort Cloud. The Kuiper belt comets still reside in the region beyond Neptune in which they formed. The Oort cloud comets formed between the jovian planets, and were flung out to great distances from the sun by gravitational encounters with the planets.

Plasma Tail

One of two tails seen when a comet passes near the Sun (the other is the dust tail.) It is composed of ionized gas blown away from the Sun by the solar wind.

Dust Tail

One of two tails seen when a comet passes near the Sun (the other is the plasma tail). It is composed of small solid particles pushed away from the Sun by the radiation pressure of sunlight.

The small bodies are subject to the gravitational whimes of the largest.

The Jovian planets shaped the asteroid belt, the Kuiper belt, and the Oort cloud, and they continue to nudge objects onto collision course with the planets

Kuiper Belt

The comet-rich region of our solar system that spans distances of about 30-100 AU from the Sun. Kuiper belt comets have orbits that lie fairly close to the planet of planetary orbits and travel around the Sun in the same direction as the planets.

Nucelus

The solid portion of a comet - the only portion that exists when the comet is far from the Sun.

What are asteroids like

asteroids are rocky leftovers from the era of planetary formation. Most are small and despite their enormous numbers their total mass is less than any of the terrestrial planets

Asteroids, Comets, and Meteorites may be small compared to planets

but they have provided evidence that has helped us understand how the solar system formed

How big can a comet be

in the Kuiper belt, icy planetesimals were able to grow to hundreds or thousands of Kilometers in size. Eris is the largest known of these objects, and Pluto is the second largest

What are the large objects of the Kuiper belt like

like smaller comets, these objects are ice-rich in composition. They orbit the Sun roughly between the orbit of Neptune and twice that distance from the Sun. Their orbits tend to be more elliptical and more inclined to the elliptic plane than those of the terrestrial and jovian planets. Many share orbital resonances with Neptune. A few, including Pluto and Eris, have moons

How are meteorites related to asteroids

most meteorites are pieces of asteroid. Primitive meteorites are essentially unchanged since the birth of the solar system. Processed meteorites are fragments of larger asteroids that underwent differentiation.

Why is there an asteroid belt

orbital resonances with Jupiter disrupted the orbits of the planetsimals in the asteroid belt, preventing them from accreting into a planet. Many were ejected but sime remained and make up the asteroid belt today. Most asteroids in other regions of the inner solar system accreted into one of the planets.