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Sunday, December 14, 2008

Planetary protection

Planetary protection is the term used to describe a guiding principle in design of an interplanetary mission that aims to prevent biological contamination of both the target celestial body and the Earth. This principle arises from the scientific need to preserve planetary conditions for future biological and organic constituent exploration – especially exobiology/astrobiology. It also aims to protect the Earth and its biosphere from potential extraterrestrial sources of contamination in the event of a sample return mission. The need for planetary protection measures is strongest for missions designed to return a sample of another planet or celestial body to the earth.


The spacecraft must be sterilized before leaving Earth in order to minimize the risk of depositing Earth-originating biological material at the destination. The return vehicle must then be designed such that the sample is returned in highly reliable "bio-container" with measures in place to dispose of any parts of the vehicle which could have been contaminated before re-entry into the Earth's biosphere.

The Committee on Space Research categorizes the missions into 5 groups:

* Category I: Any mission to Moon, Venus, metamorphosed asteroids and similar bodies.
* Category II: Any mission to comets, Jupiter, Pluto/Charon, Kuiper Belt Objects and similar bodies.
* Category III: Flyby and orbiter missions to Mars and Europa.
* Category IV: Lander missions to Mars and Europa.
* Category V: Any earth return missions.

This classification can change due to new scientific knowledge.

After receiving the mission category a certain level of biological burden is allowed for the mission. (Normally the amount of Bacillus spores per surface area is counted.)

Clean room assembly and microbial reduction through heat, chemicals or radiation are the basic techniques used to reach the microbial reduction necessary for a mission.

The discovery of extremophiles on Earth surviving temperatures that we previously thought to be lethal to all life demonstrate how difficult it can be to prevent biological contamination. It is widely claimed that a common bacterium, Streptococcus mitis, was found to have accidentally contaminated the Surveyor 3 camera prior to launch and survived dormant in this harsh environment for two and a half years . However, this claim is no longer taken seriously by NASA (see Myth of Streptococcus mitis on the moon).

Measures currently in use for scientific exploration include dry-heating of satellites, sterilizing wipes and aseptic integration of components. These add a significant burden to mission designers and integration teams. However, there is consensus that this is required to prohibit the possible microbial contamination of other planets.

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