Planetary Protection is one of my absolute FAVORITE can of worms!! Obviously it is a good idea to be careful and mindful, but I personally believe that NASA’s current policies are complete overkill.
Let’s think this through. Why don’t we want to bring earth life to another world?
Maybe because then we won’t be able to tell whether it is indigenous or not? Baloney! Imagine you accidentally bring a lizard to an island that doesn’t have them. If it is indigenous, there would be evidence of them being there in the past, through fossils or otherwise!
Maybe we don’t want to infect any life that is on that other planet, that earth life could take over that ecosystem like an invasive species? Astronomically unlikely. All earth life is evolved to live in its specific environment and to interact with the species with which it has evolved alongside. As such, totally unrelated organisms form different planets would be so completely alien to each other that they would be unlikely to interact to begin with. Additionally Mars, for example, definitively has no macro-fauna or flora. As such, any possible microbes on Mars would be completely at a loss on how to interact with humans or indeed any earth life.
Finally, Earth and Mars, for example, exchange ~500 kilograms of material every year. Analysis shows that some of that material never exceeded a temperature high enough for sterilization. Thus, if there was any life on mars, it would have reached us by now, living in our biosphere along with us.
Anyways I’m a big nerd and I hope this stuff is interesting!