Measures designed to protect the Earth (see back
contamination) and other bodies in the solar system (see forward
contamination) from cross contamination. The need for planetary protection
was first considered in 1958 (see Committee
on Contamination by Extraterrestrial Exploration), was expressed in
the Outer Space Treaty of 1967, and has
been reconsidered and refined in the light or more recent developments.
For many years, the Space Science Board
has served as NASA's primary adviser on planetary protection and quarantine.
|The Apollo 11 astronauts leave the recovery helicopter
and walk across open deck before entering their quarantine chamber
Although NASA has long had procedures in place for handling and treating
spacecraft that will land on other planetary bodies and, in some cases,
return with samples to Earth, these procedures have not always been followed.
The classic example of planetary protection measures not being followed
or implemented well was Apollo 11 –
the first manned vessel to return from the surface of the Moon.
The remote possibility existed at the time that there might be organisms
in the lunar soil which could be transferred to Earth with possibly catastrophic
consequences. Although quarantine procedures had been put in place for the
three returning astronauts, the Apollo capsule, and the lunar samples, these
were either not adequate or were breached in several instances. First the
capsule splashed down in the sea, affording the opportunity for any extremophilic
organisms on the outside of the spacecraft to enter the ocean. Second the
crane on the recovery ship which was supposed to winch the capsule and its
crew aboard was not strong enough. Third, the collected lunar dust was much
rougher than expected and had compromised the seals on the containers the
crew had brought back. So the dust was scattered in the lunar module and
capsule, making the open walk even riskier.
and sample return missions
Great care was taken to sterilize the Viking
landers that touched down on Mars in 1976.
Each spacecraft was baked for four hours before launch to kill any terrestrial
microbes adhering to them before launch. However, more recent landers and
rovers, including Pathfinder, Spirit, and Opportunity have not been so rigorously
cleansed. The discovery of the harsh conditions on Mars – its dryness,
coldness, thin carbon dioxide atmosphere, and exposure to lethal ultraviolet
– led to the requirement for absolute sterility being dropped. Also,
the delicate coatings on the high resolution cameras of these later probes
would have been destroyed by the heat of sterilization. The oven treatment
will only be applied in future to spacecraft components, such as the Phoenix
spacecraft digging arm, that bury into the Martian soil. Questions still
remain unanswered about the ability of terrestrial extremophiles to survive
current planetary protection protocols. It has been shown, in the light
of what happened with Surveyor 3 that
even ordinary Earth bacteria can survive for long periods under hostile