It's for reasons A and B, at least. There have already been issues with "B", for example: https://www.smithsonianmag.com/smart-news/crashed-spacecraft-might-hav

It's for reasons A and B, at least. There have already been issues with "B", for example: https://www.smithsonianmag.com/smart-news/crashed-spacecraft-might-have-put-water-bears-moon-180972840/ https://www.smithsonianmag.com/smart-news/crashed-spacecraft... Look at how "well" transferring species around has worked out on Earth, regardless of intentionality: https://wildlife.org/eradication-lets-rat-island-shed-its-name/ https://wildlife.org/eradication-lets-rat-island-shed-its-na... https://www.nbcnews.com/news/forget-lantern-fly-mysterious-new-pest-scientists-sounding-alarm-rcna97555 https://www.nbcnews.com/news/forget-lantern-fly-mysterious-n... ... actually, here, let's just cover things more completely/ efficiently: https://en.m.wikipedia.org/wiki/Lists_of_invasive_species https://en.m.wikipedia.org/wiki/Lists_of_invasive_species It seems wise, for multiple reasons, to try not to cross-contaminate, for the moment. Just in light of unintended consequences with past "cross-contamination" events. Something like "Andromeda Strain" may be unlikely, and, it may be that we don't find anything particularly interesting on Mars, period, say... But, we're still very early on in this phase, I'd say ... trying to avoid some of the consequences created by past explorers (who spread diseases, rats, etc. everywhere - whether European or Pacific Islander or etc.) seems prudent...