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Chemistry of Ices in Space

Molecular clouds which are dense (~106 H atoms per cm3) and very cold (3-90°K) harbor icy particles which play a crucial role in the structure and evolution of the Interstellar Matter. Stars form by contraction and fragmentation of such molecular clouds and thus the icy material gets incorporated into planetesimals which grow into planets or small remnant objects, such as comets and asteroids. The temperature gradient in the solar system determines that ices cover the surfaces of many outer solar system bodies, including planets, moons and comets as well as a large number of Kuiper belt objects located beyond Neptune.

Ices are also present on the poles of planet's Earth and Mars, outer main belt asteroids and even on permanently shaded areas of the innermost planet Mercury. The only planet which definitely does not show any evidence for ice is our sister planet Venus. The most dominant ice species throughout the universe is water ice, which is also the most intensively studied species in the laboratory. However, open questions remain whether ices produced in Earth laboratories are indeed good analogs for ices detected in space environments. Whereas temperature and pressure conditions can be relatively well controlled in the laboratory it is obviously impossible to simulate the time-scales in space environments. The bulk structure of ice, which also determines the catalytic properties of the surface, could be rather different when formed on timescales of millions of years in zero gravity in space.


Fig.: Ices in Space

In dense clouds dust particles are characterized by an icy coating. Ices cover the surfaces of many outer solar system bodies, including planets, moons and comets as well as a large number of Kuiper belt objects located beyond Neptune. Ices are also present on the poles of planet's Earth and Mars, outer main belt asteroids and even on permanently shaded areas of the innermost planet Mercury.

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