Back-contamination

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:

The main focus is on microbial life and on potentially invasive species. Non-biological forms of contamination have also been considered, including 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 has not been ruled out. In the case of forward contamination, contamination by multicellular life (e.g. lichens) is unlikely to occur for robotic missions, but it becomes a consideration in human 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 from foreign planets 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 foreign planet of origin and Earth. It would also require quarantine procedures for the materials and for anyone who comes into contact with them.

Most of the solar system appears hostile to life as we know it. No extraterrestrial life has ever been discovered, but there are 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 spacecraft 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.

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