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We could have sent seeds of life (say a few ounces of microbes) along with every planetary exploration craft. Why we haven't done that so far?

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    $\begingroup$ Have we done so inadvertently? $\endgroup$ – DJohnM Dec 17 '14 at 19:15
  • $\begingroup$ Probably, to some extent. But we can try to minimize it. $\endgroup$ – pericynthion Dec 17 '14 at 22:40
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Planetary protection is the principle that on the contrary to your proposal, we should take steps to avoid any contamination of planetary bodies with life from Earth.

There are various cited reasons for this, one of the most important being that since we don't yet know whether extraterrestrial life exists on these planets, if we accidentally or deliberately introduce terrestrial life that could confound future experiments and make it much harder to determine whether extraterrestrial life is present.

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  • $\begingroup$ That means our hopes for Mars colonization will have to wait until we are absolutely certain no life on Mars? $\endgroup$ – jorel Dec 17 '14 at 3:35
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    $\begingroup$ @jorel Yes it means, but it won't. Mars will likely be "contaminated" by humans in the 2020's or 2030's. Spreading thousands of microbe species all over the place, some of which might survive. Just like there are human hair on the Moon. After that one might maybe as well deliberately seed life on Mars. Astrobiologists need to hurry up if they want to examine a natural Mars. $\endgroup$ – LocalFluff Dec 17 '14 at 4:00
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    $\begingroup$ Contamination by humans and terrestrial microbes makes it more complicated to determine whether native life exists, but not necessarily impossible. When we have people on the planet, we'll also have the infrastructure to bring much more sophisticated lab equipment with the capability of distinguishing native from invasive species. $\endgroup$ – pericynthion Dec 17 '14 at 4:40
  • $\begingroup$ @jorel Obligatory 'relevant what-if', which talks about contamination and planetary protection. $\endgroup$ – user3334690 Dec 17 '14 at 17:50
  • $\begingroup$ @LocalFluff why worry about a stray hair when there's also human faeces on the moon. $\endgroup$ – Nick T Dec 17 '14 at 22:11
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As noted, there is a strong desire to NOT send terrestrial 'anything' to other planets.

They spend a LOT of money and time properly sterilizing space craft that land or might crash land into other planets. Now you might say, this vehicle will be in interplanetary space for 1-2 years in transit, surely nothing can survive.

Yet amusingly odd stuff has been found to survive on the surface of the ISS for years since launch. (Something about sea plankton DNA?).

Elon Musk has told the story many many times, that his initial plan before starting SpaceX was to build a contained greenhouse as part of a Mars lander, so that on landing it would add water and starting growing green things on the red planet.

Once he realized the issue was not enthusiasm but rather launch costs, he abandoned that approach and instead focused on launch costs via SpaceX. (Which he has succeeded at spectacularly so far! Everyone is forced to drop launch costs, Chinese do not think they can compete. Ariane 6 is designed specifically to try to compete. If the landing succeeds on any of the launches in the coming years, and they are able to refly first stages it is likely his success will become only greater).

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