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Interplanetary contamination refers to biological contamination of a planetary body by a space probe or spacecraft, either deliberate or unintentional. There are two types of interplanetary contamination: *''Forward contamination'' is the transfer of life and other forms of contamination from Earth to another celestial body. *''Back contamination'' is the introduction of extraterrestrial organisms and other forms of contamination into Earth's biosphere, it also covers infection of humans and human habitats in space and on other celestial bodies by extraterrestrial organisms, if such exist. The main focus is on microbial life and on potentially invasive species. Non biological forms of contamination have also been considered including e.g. contamination of sensitive deposits (such as lunar polar ice deposits) of scientific interest by rocket exhausts. In the case of back contamination, multicellular life is thought unlikely but not been ruled out, and in case of forward contamination, then again, forward contamination by multicellular life (e.g. lichens) becomes a consideration in human missions, though unlikely for robotic missions. Current space missions are governed by the Outer Space Treaty and the COSPAR guidelines for planetary protection. Forward contamination is prevented primarily by sterilizing the spacecraft. In the case of backward contamination, however, the aim of the mission is to return biological material to Earth if such exists, and sterilization of the samples would make them of much less interest. So back contamination would be prevented mainly by containment, and breaking the chain of contact between the planet and Earth. It would also require quarantine procedures for the materials and for anyone who comes into contact with them. ==Vulnerability of the Solar System to contamination == Most of the solar system appears hostile to life as we know it. No extraterrestrial life has ever been discovered, but there are however several locations outside Earth, where life could possibly exist, have existed or thrive if introduced. If extraterrestrial life exists, it may be vulnerable to interplanetary contamination by foreign micro-organisms. Some extremophiles are able to survive space travel to another planet and foreign life could possibly be introduced by spacecrafts from Earth for example. If extraterrestrial life does not exist, but could potentially thrive in a given location, the site is also considered vulnerable to contamination. In this case the introduction of life, could transform the location from its current pristine state. Locations within the Solar System, where life might exist today include the ocean of liquid water beneath the icy surface of Europa, the interior of Enceladus which is currently sending water into space, and the possible ocean of liquid water which some astronomers believe might exist beneath the surface of Titan (its surface has oceans of liquid ethane / methane, but it may also have liquid water below the surface and ice volcanoes).〔(COSPAR Workshop on Planetary Protection for Outer Planet Satellites and Small Solar System Bodies ) European Space Policy Institute (ESPI), 15–17 April 2009〕〔(COSPAR power point type presentation, gives good overview of the detailed category decisions )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Interplanetary contamination」の詳細全文を読む スポンサード リンク
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