Astronomy 8

This is the distance from the Sun where ice can exist as a solid because it is not vaporized by the Sun.

Dust tail is small solid particles (dust) which is pushed away from the Sun by the solar wind. The dust tail is curved and has a reddish color. The gas (or plasma) tail is composed of gas molecules – they are not affected by the solar wind but are pushed by light from the Sun. This tail typically has a blue color.

Kuiper reasoned that short period comets must have a lifetime (a few million years at most) which is short compared to the age of the solar system. Therefore these comets must be continuously replaces. Since the aphelions of these comets are out past Neptune he reasoned that there must be a reservoir of comet-like objects at there which are occasionally perturbed so there orbits are shifted into the inner solar system.

Minor planets are objects which are spherical like planets but they are not large enough to sweep all other small bodies from the same region. Examples are Pluto, Eris and Ceres.

The difference between the differentiated and undifferentiated meteorites is differentiated meteorites come from bodies which melted and denser material sunk to the bottom. The undifferentiated meteorites are bodies which show no signs of having melting.

The bodies in space follow the same orbits as the comets they came from. When the Earth passes through the orbit of the comet a meteor shower occurs. Since these dates are well known it is relatively easy to predict when a meteor shower occurs. However, it is difficult to predict the number of meteors which will be seen.

Jupiter is outside the ice line so its core could form from both silicate and icy planetismals. In the early solar system there would have been many more of these objects therefore larger planets outside the ice line.

Ice is vaporized inside the ice line therefore the planetismals forming the terrestrial planets contained little water and as a consequence the inner planets have relatively little water.

An Earth-crossing asteroid is an asteroid whose orbit crosses the Earth’s orbit.

Comets are a mix of silicates, ices, and organic materials.

Many comets will end up going to close to the Sun and being destroyed. Some will eventually lose all of their ice after multiple passes into the inner solar system and will become similar to asteroids.

The solar system and Sun started as a very large rotating gas cloud. The cloud began contracting under its own gravitation. As it shrinks most of the mass ends up in the central mass of the star however some material ends up in a disk which is revolving around the central proto-star. Next, as the disk gets denser some materials like silicates and ices begin condensing (solidifying) into dust. The dust particles begin to combine into larger masses (planetesmals). The planetesmals then combine to form the planets.

The Late Heavy Bombardment is a time about 4 billion years ago (not accepted by all planetary scientists) when the number of impactors increased significantly. During this time the large impact basins formed (including the lunar maria). This may have occurred due to the outward motion of Jupiter.

The basic idea is the early Earth was impacted by a Mars sized body which knocked off a large amount of debris. This debris ended up in a disk around the new Earth (a merger of the old Earth and most of the impactor). The disk coalesced into the Moon.

Light pressure from the star pushes it away.