Study, 002-Comets

■ Introduction

- An icy small solar system body: loose collection of ice (frozen water and CO and other gases), dust, rock

- Potato-shaped, dark black surface

- Diameter: 100-200 m (small comets), 10-100 km

- Comet splitting: some comets, fragile nucleus, due to thermal stress, internal gas pressure, impact

- Nucleus of Comet Temple 1:

- On highly elliptical orbits with the Sun at one focus.

■ Origin

- Millions of years before planet formation.

- Pairwise low velocity accretion of weak cometesimals.

- A remnant of the original planetsimal "building blocks" from which the planets grew.

- Short-period comets: Comet Halley, < 200 years. Orbital paths are in the same direction and close to the same plane of orbit as Earth. Believed to originate in the Kuiper belt, a disk-shaped region extending beyond Neptune.

- Kuiper (카이퍼) belt: contains small, icy planetary bodies. Occasionally the orbit of a Kuiper belt object will be disturbed by the interactions of the giant planets in such a way that it will have a close encounter with Neptune and either be flung out of the solar system or pushed into an orbit within our solar system.

- Long period comets: Comet Hale-Bopp, Comet Hyakutake. > 200 years. orbital path is random in terms of direction and plane of orbit. Believed to originate in the Oort cloud.

- Oort cloud: a spherical envelope that may extend 30 trillion kilometers ( beyond our Sun. Oort cloud objects have never been imaged.

The Helix Nebula has a cometary Oort cloud.

- When passing close to the Sun, it warms and begins to evolve gasses:

A comet loses between 0.1 and 1 percent of its mass each time it orbits the Sun.

Coma: cloud (atomosphere) around the comet nucleus, up to 80,000 km in radius

Tail: up to 10⁶ km. due to Sun's radiation pressure and solar wind acting on the coma

Dust trail

Dust tail: whitish yellow. small, solid particles that are about the same size found in cigarette smoke. Because the pressure from sunlight is relatively weak, the dust particles end up forming a diffuse, curved tail.

Ion gas tail (= plasma tail): blue. ionized CO gas. UV of sunlight rips one or more electrons from gas atoms in the coma, making them into ions.. The solar wind then carries these ions straight outward away from the Sun. The resulting tail is straighter and narrower.

- Comet Hale-Bopp, shortly after passing perihelion in April 1997

[Ref]

Introduction: nasa, jewitt