What Happened With Mars Sample Return? (I)

Say you want to study a bunch of alien rocks. Our planet is rich in scientists and sophisticated rock-examining machinery, so one approach is to put them all on a rocket and send them to where the rocks are. But our best machines are big and too delicate to fit on a rocket, and the scientists themselves are fragile—we have managed to keep a few of them alive in low Earth orbit, but they struggle to get any science done there. So another idea is to bring rocks back home. And so sample return has been a top goal of planetary science for thirty years or more. There have been some successes! Most famously, the Apollo astronauts brought back a few hundred kilograms of moon rocks. In 2004, a mission called Stardust flew past the comet Wild 2 and brought back dust grains from the comet’s coma. In 2005, the Japanese Hayabusa probe landed on an asteroid called 25143 Itokawa and brought back a little surface dust for study. Its successor, Hayabusa2, did the same for an asteroid called 162173…