Moon dust is dangerous. Each mote is like a tiny shard of glass—there’s no wind or rain to soften the edges of lunar soil. During the Apollo missions, it jammed equipment and got stuck in the seals of space suits, causing a serious loss of pressure. Martian dust poses its own hazards. On the Red Planet, swirling dust storms have covered rovers’ solar panels, significantly reducing their power while they waited for a favorable gust of wind. And if these kinds of space dust get into an airlock, forget it: It can be toxic or irritating to the lungs and could endanger astronauts’ health on long missions.