Cleanliness in space and materials and samples brought back is a critical aspect of space exploration. Being responsible travelers and explorers in space we don't want to contaminate alien environments. And we certainly don't want any contamination of the samples that are returned to Earth for analysis. If we are careless there, then the whole value of any mission would be worthless: Bad data and false conclusions including the time and costs of the mission. Thus great effort has been made to make our trips of humans, probes, tools, collection apparatus, etc. as contamination free as possible. Think back to Robert Wise's 1971 film "The Andromeda Strain" when the selected investigation crew had to endure hours of decontamination of their bodies to enter a safe area to scientifically discover the deadly alien biological anomaly that occurred on the surface and the attempts to isolate the only two survivors in an environment free of contamination. And as current and real as of the 9th of September when the Genesis probe will return to Earth loaded with solar dust; the containment of the samples will be placed in the highest contamination environment possible: "Genesis is the first NASA mission to develop a class 10 cleanroom (only 10 particles of contaminant per cubic meter)." And the situation works the other way: Squeaky clean items placed in space are desired and accidents do happen. On April 20, 1967 the Surveyor 3 spacecraft landed on the moon with a strain of Streptococcus mitis on board. The bacteria is common and harmless: Someone must have sneezed and there was a breech in the quest for a "zero contamination" assembly environment. The freeloader was discovered when in 1969 the Apollo 12 astronauts retrieved a sample of some circuit board insulation and brought it home for analysis. Now the bacteria was free-dried on the Moon's surface but rebounded back on Earth. Maybe no harm done on the Moon, but extra care must be exercised when visiting systems that would sustain any bacteria and allow reproduction. As a matter of fact, many scientists don't think a "zero contamination" system is possible. Consider also that contamination can be inorganic. And from an epistemological perspective, data received from contaminated materials is always suspect. The recent Genesis crash is a prime example. Certification of the purity of samples is nearly impossible.