NASA's Perseverance rover has been carrying little squares of spacesuit fabric around Mars for years. Now scientists have used them to measure something future astronauts will have to breathe around: Martian dust fine enough to get deep into the lungs and into the bloodstream.

A close up of the SHERLOC calibration target on NASA's Perseverance rover, with its spacesuit material swatches. Image: NASA/JPL-Caltech/MSSS