Perseverance: Did you know?
Witness Tubes
Perseverance must meet extraordinary cleanliness requirements to avoid contaminating Martian samples with terrestrial contaminants that may have inadvertently been brought from Earth. Strict rules limit the amount of inorganic, organic, and biological materials from Earth in the rover and its sample handling system.
Perseverance carries five “witness tubes” along with sample collection tubes. The witness tubes are like sample tubes except they are preloaded with various materials that can capture molecular and particulate contaminants, such as:
– Gasses that may be released, or “outgassed,” from materials on the rover;
– Chemical remnants from the firing of the landing propulsion system;
– Any other Earthly organic or inorganic material that may have arrived on Mars with the rover.
In the future, if the Perseverance samples are returned to Earth for analysis, the witness tubes would show whether Earth contaminants were present during sample collection. This would help scientists tell which materials sampled may actually be of Earth origin.
