Where does the water on Earth ?

Water from asteroids

Without water, life as we know it on Earth could never scale up to us.
Comets are composed mostly of frozen water surrounding a solid core, which is led to believe that the water had been brought by comets.
To know the composition of these frozen bodies several scientific missions have been launched.
In January 2005 NASA sends a spacecraft toward comet Tempel 1.
The Deep Impact mission, with 2 gears, the comet reached 14 km in diameter to analyze its composition in the powerful 36 000 km/h while the other vehicle films the impact and mass ejections.
Scientists have noticed that the water in comets is not the same composition as that of our oceans. Most of the water on Earth come from asteroids and micrometeorites 40 000 tones of which fall on Earth every year.

The massive meteor showers have produced Earth's atmosphere. The water content of hydrated minerals in meteorites is identical to that of terrestrial water when no other known extraterrestrial bodies do not show this feature.
According to Michel Maurette, CNRS researcher is analyzing the neon, nitrogen, carbon dioxide and water that scientists have found that these micrometeorites had also produced Earth's atmosphere.

Image: Deep Impact is NASA's spacecraft, which studied the composition of the comet Tempel 1.
On July 4, 2005, onboard with the impactor probe struck the comet with success, which caused a crater about 30 meters in diameter and ejection of several tons of materials from his basement.

Water extraterrestrial matter

Water is not the result of fumes emitted during the intense volcanic activity from the beginning of the creation of our planet.
Francis Albarède, geochemist French member of the Academia Europaea, the water is not part of the initial inventory of the Earth but from the stirring maintained in the outer solar system by giant planets.
The mantle rocks are poor in water, geochemists evaluate its concentration in two hundredths of a percent. It is the same on the sister planet of Earth, Venus and Mars. This is the main reason cited by Francis Albarède.
During the formation of the Solar System, the temperature would never come down low enough, in the space between the Sun and Jupiter's orbit, so that the volatile elements can condense with the material world. The arrival of water on Earth would therefore correspond to a late episode of planetary accretion.

The terrestrial planets are formed by agglomeration of asteroids, a few million years.
This constant bombardment from the beginning is between objects located between the Sun and the asteroid belt. This space windswept electromagnetic young Sun is too hot for water and volatiles are condensed. This distribution of material is used to clean the dust on its solar system by concentrating the material in the planets in formation.
The gravity of giant planets distributed in all directions, asteroids covered with ice.

NB: By Francis Albarède, French geochemist, water is not part of the initial inventory of the Earth but from the stirring maintained in the outer solar system by giant planets.  

Image: Image of artist, the water came from space...

In search of dust

The mission of the spacecraft STARDUST (stardust), launched by NASA February 7, 1999, was to collect interstellar dust.
It passed through the tail of Comet Wild 2 in January 2004 and returned to Earth Jan. 15, 2006 after collecting a large amount of cometary and interstellar dust. This is the first probe to be brought back comet particles, it has traveled 4.5 billion km in the solar system.
The new mission of the Stardust spacecraft, since July 2007, is the flyby of Comet Tempel 1 that it will reach 14 February 2011.
Tempel1 was deliberately struck by the impactor of the Deep Impact spacecraft to obtain more information on cometary dust and interstellar particles.
Stardust is 1.7 m long, 66 cm wide and deep, and weighs 385 kg (254 kg for the probe, 46 kg for the return module and 85 kg of fuel).
The work of analyzing photographs taken by STARDUST is huge.

That's why NASA launched the Stardust @ home calling for help the Internet community. Stardust @ home volunteers encourages users to search for interstellar dust impacts through a virtual microscope.

Image: The particle collector (Aerogel sample collector) is on the Stardust SRC (Sample Return Capsule), the return capsule. The different dust is captured in the Aerogel, resembling foam. The collector is approximately 1m ² surface on which is fixed Aerogel.
One side is used to collect interstellar particles, and the other to that of cometary particles. When a particle at high speed in contact with Aerogel, it enters into a cone digging more than 200 times its own length.