10th April 2011 Plantery Systems

In the middle of the asteroid belt, which is the white dotted region in the image below, is the frost line (aka snow line or ice line).   It's about 2.7 AU (astronomical units) from the sun. 2.7 AU is approximately 4 x 10⁸. An astronomical unit is approximately the mean distance from Earth to the Sun.

The frost line is the distance at which hydrogen compounds such as water, methane and ammonia exist as ice. This temperature at which this occurs is estimated to be below about 150 K.

from Wikipaedia

This line separates the Jovian planets, Jupiter, Saturn, Uranus and Neptune from the terrestrial planets.  Jovian planets are not primarily composed of solid matter such as rock, but of gases.  The are also called gas giants.

Planet Types

By Size

Size Min	Size Max	Name
>1 Earth Mass	<10 Earth Masses	Super earth or gas dwarf
>10 Earth Masses	<13 Jupiter Masses	Gas giant
>13 Jupiter Masses	< Mass of small star	Brown dwarf (Note: able to start deuterium fusion)

By Composition

Name	Description	Example
Silicate planet	A planet made mostly of silicon based rocky mantle with an iron core.	Earth
Iron planet	A theoretical type of planet consisting of almost only iron which thus has higher density and a smaller radius than other terrestrial planets of comparable mass. They are believed to form in the high density region close to a star if the protoplanetary disk is rich in iron.	Nearest to this is Mercury whose metallic core is about 60-70% of its mass.
Coreless planet	A theoretical type of terrestrial planet that consists of silicate rock but has no metallic core. Coreless planets are believed to form farther from the star where volatile oxidizing material is more common.	Chondrite asteroids and meteorites
Carbon planet or diamond planet	A theoretical type of terrestrial planet, composed primarily of carbon-based minerals.	Carbonaceous asteroids

Astronomy Without A Telescope – Our Unlikely Solar System