The Perseverance rover contains 43 sample tubes for collecting Martian soil and rock samples that will eventually be returned to Earth. The tubes have been extensively cleaned, so their contents reflect the actual conditions of Mars and not contaminants from Earth.

It is good scientific practice to process an empty container as an experimental control. Such a control can help evaluate whether contamination or other issues have occurred. Are any of the sample tubes expected to be returned empty as an experimental control?

(The five additional "witness tubes" are designed as a kind of control, so an answer explaining them would get my upvote. However, they are not empty, so such an answer will not get the checkmark.)


  • $\begingroup$ Let's examine the premise of your question. It is the samples that will be examined; the contents of the tube. Witness sample particulates present surfaces upon-which contaminants can adhere. How could an empty tube serve as a control, there is no material in it to test in the same way that samples and witnesses are tested. If "it is good scientific practice to process an empty container", 1) can you outline how that's done in general (what would "process" mean) 2) how might it be doable in this case? $\endgroup$ – uhoh Apr 1 at 7:47
  • $\begingroup$ @uhoh: Empty or full, you can still examine the gases in and wall of the tube. $\endgroup$ – DrSheldon Apr 1 at 12:29
  • $\begingroup$ Well, doesn't a gas-filled or evacuated tube still count as a "witness" ? So far as I know, these sample tubes are designed for solids, not for evaluating the Martian atmosphere. $\endgroup$ – Carl Witthoft Apr 1 at 12:44
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    $\begingroup$ @CarlWitthoft: No. "The witness tubes are similar to the sample tubes except they are pre-loaded with a variety of witness materials that can capture molecular and particulate contaminants" Also "Once the tube is hermetically sealed, nothing can enter or leave it." source If you want to write up an answer about the witness tubes, I said I would upvote it, but my question is really about empty tubes. $\endgroup$ – DrSheldon Apr 1 at 13:13

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