This is a really interesting topic, in my opinion.  And something that I hadn’t thought about until now, but biological contamination is a real thing and I’m not just talking about on our planet.  How does NASA defend against microbial invaders from outer space?  Conversely, how can NASA prevent biological contamination from Earth to outer space? When some kind of organism reaches the Earth, it’s called backward contamination.  When it leaves the Earth and goes somewhere else, it’s known as forward contamination.  I’m talking about organisms getting attached to a spaceship, for example.  In 1958, the U.S. National Academy of Sciences (NAS) – not to be confused with NASA – issued a decree urging “that scientists plan lunar and planetary studies with great care and deep concern so that initial operations do not compromise and make impossible forever after critical scientific experiments”.

Think about it though. When astronauts are traveling to other planets, any number of organisms could be floating around waiting to attach themselves to the astronaut or the spaceship.  And when they come back to Earth, there is no way of knowing what will happen.  In 1959, the newly formed Committee on Space Research (COSPAR) argued: “that all practical steps should be taken to ensure that Mars be not biologically contaminated”.  And there’s that as well.  What are astronauts taking for our planet to another?  I should qualify that – it’s not just astronauts or spaceships.  The Mars Rover, for example, could be carrying something on it. The COSPAR recommendations became law in 1967 when the US, USSR (at the time) and the UK had all signed into the United Nations Outer Space Treaty.


Dr. Lucianne Walkowicz, an astronomer at Alder Planetarium and the Astrobiology Chair at the Library of Congress puts this into perspective. “When we bring spacecraft to other worlds (or eventually human beings), we want to make sure that we understand that environment. That means being relatively cautious about contaminating it.”  But not every planet or extraterrestrial target requires the same degree of caution.  In fact, COSPAR has developed a 5-category system that space agencies must adhere to when they’re developing their planetary probes.

  • Category I covers places with little chance of finding even basic forms of life, like Mercury.
  • Category II includes places that might be explored for the origins of life but where the chances of contamination by Earthly microbes is remote. Think Venus or the Moon.
  • Category III regulates flyby and orbiter missions where the chances of contamination are moderate, like Mars or Europa. This is why Cassini was thrown into Saturn: we couldn’t have it falling into Enceladus or Titan.
  • Category IV regulates lander or probe missions to the same places as category III, though it is further divided into a series of subclasses based on specific regions of the planet’s surface and what the lander is actually looking for.
  • Category V is what happens if there’s a good chance we’ll pick something up in space. It demands “absolute prohibition of destructive impact upon return, containment of all returned hardware which directly contacted the target body, and containment of any unsterilized sample returned to Earth.”

This planetary protection scheme is designed to minimize the damage from both forward and backward contamination perspectives.  The argument could be made, however, that these protocols wouldn’t make a difference.  There is the possibility that microorganisms that are trying to hitch a ride from Mars might be ill-equipped to handle the rigors of interplanetary flight.  But that’s not something we really know for sure. Either way, I think having some type of protocol in place is going to be beneficial in the event that it could happen.

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