One of the reasons people are so interested in Mars is that it might once have harbored life. It’s even possible that life exists there today, somewhere under the surface. If we do ever find signs of life on Mars, we’ll want to know whether it originated on that planet, rather than being the result of contamination from Earth. To make that distinction, astrobiologists on Earth have been trying their best to sterilize everything we send into space. However, Alberto Fairén of Cornell University and Dirk Schulze-Makuch of Washington State University think we shouldn’t bother. In all likelihood, Mars has already been contaminated with Earth species.
Alberto Fairén, & Dirk Schulze-Makuch (2013). The overprotection of Mars Nature Geoscience DOI: 10.1038/ngeo1866.