It’s a major component of solid rocket propellants. It allows water to exist as liquid on Mars, despite atmospheric pressure at the Martian surface being roughly 0.6 percent that on Earth. It also can be broken down to release oxygen that astronauts and future colonists in a Mars settlement could breathe.
It’s called perchlorate and it’s abundant on Mars –10,000 times more abundant in Martian dirt than in soils and sands of Earth. That may sound like a good thing, considering the useful p