NASA created a Martian Dust Limit Working Group this year to figure out how much Mars dust a person can safely breathe, and Leonard David reports for Space.com on the dust hazard and how future astronauts might deal with it. The Apollo missions showed that dust is a real problem. "On Mars, dust particles are a little more rounded, not as jagged and cutting into you. Mars dust also carries silica and heavy metals, both of which cause cancer. No real Mars dust has ever been brought back for testing, so the limit rests on lunar toxicology, simulated soils, and rover measurements.