system
Given the following post, respond as if you're commenting on Reddit:
human
When we visit other moons or planets in the search of life, how do avoid bringing bacteria or other microorganisms with us?

What if we do, and the microorganisms essentially become invasive species?

If thats the case, then how would we tell the difference between an organism from Earth and an organism that had its origins on the celestial body we’re studying?
gpt
This is actually a large issue NASA has had to deal with. It is an international law that all spacecraft must be cleaned to avoid contamination. 

They use a variety of compounds and radiation to kill microbes and bacteria but the unfortunate thing is some microbes are very, very hardy. Some bacteria love radiation and NASA even found that a bacteria was surviving in one of their clean rooms by consuming one of their own cleaning products. It is virtually impossible to remove all life from the surface of an object. 

Current NASA standards are up to 300,000 spores from the exposed surface of a landed spacecraft and a maximum density of 300 spores/m^2. There are also zones on mars that are quarantined from all spacecraft and extraterrestrial life to avoid contamination.