Vacuum

For other uses, see vacuum cleaner and Vacuum (musical group).

Vacuum in space

Much of outer space has the density and pressure of an almost perfect vacuum. It actually is a tenuous plasma containing a small number of ionized atoms per cubic metre, the most common being hydrogen (H+) and helium (He++) and an equal number of free electrons. The interstellar medium also contains enough dust to affect astronomical measurements. The properties of a vacuum may suggest that space is a very good insulator; in reality, the plasma of outer space is highly electrically conductive which may give rise to many complex phenomena.

Related Topics:
Outer space - Plasma - Hydrogen - Helium - Interstellar medium

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All of the observable universe is also filled with large numbers of photons, the so-called cosmic background radiation, and quite likely a correspondingly large number of neutrinos. The current temperature is about 3 K, being merely 3 degrees above the absolute zero of temperature. Neither these photons nor the neutrinos produce a significant interaction with matter, so stars, planets and spacecraft move freely in this near perfect vacuum of interstellar space.

Related Topics:
Universe - Photon - Cosmic background radiation - Neutrino - Temperature - K - Absolute zero - Spacecraft

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Stars, planets and moons keep their atmosphere by gravitational attraction, so atmospheres have no firm boundary. The density of gas decreases with distance from the object. In Low Earth Orbit (about 300 km altitude) the atmospheric density is still sufficient to produce significant drag on satellites. Most Earth satellites operate in this region, and they need to fire their engines every few days to maintain orbit. The atmosphere in Low Earth Orbit is increasingly being polluted with man-made debris. Studies have discovered that some satellites retrieved from orbit are coated with a very thin layer of urine and fecal matter evidently released from Russian and US space missions. http://see.msfc.nasa.gov/sparkman/Section_Docs/article_1.htm

Related Topics:
Low Earth Orbit - Urine - Fecal matter - Russian - US

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Beyond planetary atmospheres, the pressure from photons and other particles from the sun become significant. Spacecraft can be buffeted by solar winds, but planets are too massive to be affected. The idea of using this wind with a solar sail has been proposed for interplanetary travel.

Related Topics:
Solar winds - Solar sail

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The deep vacuum of space could make it an attractive environment for certain processes, for instance those that require ultraclean surfaces.

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In 1913, Norwegian explorer and physicist Kristian Birkeland may have been the first to predict that space is not only a plasma, but also contains "dark matter". He wrote: "It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. We have assumed that each stellar system in evolutions throws off electric corpuscles into space. It does not seem unreasonable therefore to think that the greater part of the material masses in the universe is found, not in the solar systems or nebulae, but in "empty" space. (See "Polar Magnetic Phenomena and Terrella Experiments", in The Norwegian Aurora Polaris Expedition 1902-1903 (publ. 1913, p.720)

Related Topics:
Kristian Birkeland - Plasma

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