system
Given the following post, respond as if you're commenting on Reddit:
human
If we find life on Mars, how will we know it didn't come from tiny organisms on any of the rovers?
gpt
NASA has "planetary protection" protocols whereby rovers are meticulously sterilized before being loaded into the rocket, and the payload bays are air-tight.  The protocols are especially strenuous for Mars and other destinations considered prime candidates for exobiology.  

The agency is so focused on this principle that, for instance, the Cassini spacecraft will be crashed into Saturn to avoid even the possibility that it will some day crash into Titan or Enceladus and contaminate them somehow.  The Juno spacecraft will likewise be crashed into Jupiter to avoid possibly contaminating Europa.