Here on Earth every object, every surface is “contaminated”; bacteria and viruses are ubiquitous. Since these organisms have evolved along with the rest of us, our resistance is high to the vast majority. We are accustomed to the presence of microorganisms and indeed could not survive without them.
However, we know nothing about the ecology of other planets. We do not even know with certainty that any form of life exists anywhere else in the universe, although statistically the likelihood is extraordinarily high. And the discovery of any form of life on any other planet will strengthen the belief that there are, throughout the universe, many life-bearing planets. The search for life has a high priority in plans for future exploration of the solar system, and at the present time Mars seems without question to be the planet most likely to possess biological activity.
Polluting the Universe. JAMA. 2016;316(12):1321. doi:10.1001/jama.2015.17103