Cross-contamination, aaaaaaaaah!

I'm going to begin with the session's final talk because it's the one that has caused the most controversy. A week ago Adam Mann posted an article at Science provocatively titled "NASA ‘clean’ room is contaminated with fungus". The article is fine but apparently NASA Headquarters was unprepared for the media response to the title and now some of the poor astromaterials curators at Johnson Space Center (JSC) are feeling the heat. Let me reassure you that what Aaron Regberg reported at LPSC is (a) entirely unsurprising and (b) actually part of a responsible and diligent approach to avoiding future problems with the precious samples they will be receiving from asteroids Bennu and Ryugu. This will be longish but I want to set the record straight by paraphrasing Regberg's talk from my notes. [Abstract #2056]

JSC maintains seven extraterrestrial sample collections. From "dirtiest" to "cleanest", as far as I understand it, they are: meteorites collected on Earth; cosmic dust collected at high altitude; microparticle impacts on ISS; lunar samples; and the super-tiny and precious collections from each of Hayabusa, Stardust, and Genesis. Each of these seven collections has its own separate clean lab to avoid cross-contamination.

It may surprise you to find out that JSC is "generally not worried" about microbial contamination above and beyond the usual, stringent clean-room standards. Consider meteorites collected on Earth. These are 100% certain to be contaminated with microbes. At the other end of the spectrum, consider things like solar wind atoms (from Genesis), where microbes would be much larger than the samples and so are "not an issue." But they now have to consider microbial contamination more specifically, Regberg said, because with OSIRIS-REx and Hayabusa2 soon to be bringing back pristine samples from carbon-rich asteroids, and future plans to bring samples back from Mars, we want to maintain sterility of all of those samples.

How clean does a lab have to be? Regberg explained International Standards Organization (ISO) clean room standards. The standard is a measure of how many particles are in a cubic meter of air; it's a little complicated because particles come in different sizes. But the gist is that the lower the ISO number, the cleaner the air, and it's a logarithmic scale: an ISO 5 clean room can have 10 times more particles in its air than an ISO 4 clean room can. (Read more about ISO clean room standards on this industry website.)