Editing Water (section)

==Distribution of water in nature==

===Water in the Universe===
Much of the universe's water may be produced as a byproduct of star formation. When stars are born, their birth is accompanied by a strong outward wind of gas and dust. When this outflow of material eventually impacts the surrounding gas, the shock waves that are created compress and heat the gas. The water observed is quickly produced in this warm dense gas. Water has been detected in interstellar clouds within our galaxy, the Milky Way. It is believed that water exists in abundance in other galaxies too, because its components, hydrogen and oxygen, are among the most abundant elements in the universe. Interstellar clouds eventually condense into solar nebulae and solar systems, such as ours.

Water vapor is present on:
* Mercury - 3.4% in the atmosphere, and large amounts of water in Mercury's exosphere
* Venus - 0.002% in the atmosphere
* Earth - trace in the atmosphere (varies with climate)
* Mars - 0.03% in the atmosphere
* Jupiter - 0.0004% in the atmosphere
* Saturn - in volatiles|ices only
* Enceladus (moon of Saturn) - 91% in the atmosphere
* exoplanets known as HD 189733 
Liquid water is present on:
* Earth - 71% of surface
* Moon - small amounts of water have been found (in 2008) in the inside of volcanic pearls brought from Moon to Earth by the Apollo 15 crew in 1971

Strong evidence suggests that liquid water is present just under the surface of Saturn's moon Enceladus. Probably some liquid water is on Europa.

Water ice is present on:
* Earth - mainly on ice sheets
* polar ice caps on Mars
* Titan (moon)|Titan
* Europa (moon)|Europa
* Enceladus (moon)|Enceladus

Probability or possibility of distribution of water ice is at: lunar ice on the Moon, Ceres (dwarf planet), Tethys (moon). Ice is probably in internal structure of Uranus, Neptune, and Pluto and on comets.

===Water and habitable zone===

The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth is vital to the existence of life on Earth as we know it. The Earth is located in the habitable zone of the solar system; if it were slightly closer to or further from the Sun (about 5%, or about 8 million kilometres), the conditions which allow the three forms to be present simultaneously would be far less likely to exist

Earth's mass allows gravity to hold an Celestial body atmosphere|atmosphere. Water vapor and carbon dioxide in the atmosphere provide a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were smaller, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars).

It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying levels of incoming solar radiation (insolation), indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the ''Gaia hypothesis''.

The state of water also depends on a planet's gravity. If a planet is sufficiently massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity. There are various theories about origin of water on Earth.