Terrestrial Planet
From Jolkein
A terrestrial planet is a planet who is mainly made up of a solid surface. Typically they range between 1,000 km to 30,000 km in diameter. Life is generally more likely to develop in terrestrial worlds than any other planetary categories. There are 2 types of planets under this category, they are Rocky Planet and Ice Planet
[edit] Rocky Planet
A terrestrial planet, telluric planet, or rocky planet is a planet that is composed primarily of silicate rocks or metals. Terrestrial planets have a solid planetary surface, making them substantially different from the larger giant planets, which are composed mostly of some combination of hydrogen, helium, and water existing in various physical states.
All terrestrial planets have the same basic type of structure, such as a central metallic core, mostly iron, with a surrounding silicate mantle. Terrestrial planets can have canyons, craters, mountains, volcanoes, and other surface structures, depending on the presence of water and tectonic activity. Terrestrial planets have secondary atmospheres, generated through volcanism or comet impacts, in contrast to the giant planets, whose atmospheres are primary, captured directly from the original solar nebula.
[edit] Icy Planet
An ice planet is a type of planet with an icy surface of volatiles such as water, ammonia, and methane. Ice planets consist of a global cryosphere. Ice planets usually appear nearly white. An ice planet's surface can be composed of water, methane, ammonia, carbon dioxide (known as "dry ice"), carbon monoxide, and other volatiles, depending on its surface temperature. Ice planets would have surface temperatures below 260 K (−13°C) if composed primarily of water, below 180 K (−93°C) if primarily composed of CO2 and ammonia, and below 80 K (−193°C) if composed primarily of methane.
On the surface, ice planets are hostile to life forms because they are extremely cold. Many ice worlds likely have subsurface oceans, warmed by internal heat or tidal forces from another nearby body. Liquid subsurface water would provide habitable conditions for life, including fish, plankton, and microorganisms. Subsurface plants as we know it could not exist because there is no sunlight to use for photosynthesis. Microorganisms can produce nutrients using specific chemicals (chemosynthesis) that may provide food and energy for other organisms. Some planets, if conditions are right, may have significant atmospheres and surface liquids which could be habitable for exotic forms of life.
