Argument: Manned mission to Mars necessary to reveal underground life
Glenn Zorpette. "Why Go to Mars?" Scientific American. March 2000: "Another reason why humans may have to be on site to conduct a thorough search for life stems from the fact that if any such life exists it is probably deep underground. Upcoming probes will be equipped with robotic assemblies that can bore several centimeters into rocks or dig a few meters down into the soil. But barring any discoveries at those shallow depths, researchers will have to bring up samples from hundreds of meters below the surface, maybe even one or two kilometers down, before they can declare Mars dead or alive. Drilling for samples at such depths 'most likely will require humans,' says Charles Elachi, director of the Space and Earth Sciences Program at the Jet Propulsion Laboratory in Pasadena, Calif."