The factories churned out something else, too: radioactive waste. At the U.S. plant on the South Carolina-Georgia border, workers dumped tens of millions of gallons of radioactive waste a year into open-air basins. The worst of the stuff, 37 million gallons of radioactive sludge, salt and liquid waste, was put into underground storage tanks, where it sits to this day. The site, known as Savannah River, is still heavily contaminated, and clean-up operations have run to many billions of dollars.

In Russia, the situation is even grimmer. In true Soviet fashion, the bomb makers secretly dumped unknown quantities of liquid waste into giant reservoirs around the plant. Nobody knows how much radioactive contamination is out there, but a single accident — the explosion of a waste tank in 1957 — is thought to have been Chernobyl-like in scale. As recently as the 1990s, the plant was spewing radioactive waste at a rate that makes the leaks of radioactive water from the melted-down Fukushima power plant look like a bubble bath. Residents living around the plant have elevated rates of leukemia and genetic mutations. Their children get cancer.

The United States quit making plutonium in the late 1980s, after it became apparent that both sides had stockpiled enough warheads to destroy civilization. At first, NASA was able to draw on the supply of plutonium-238 left over at Savannah River, but that soon ran out. So it turned to Russia. The first shipment from the Russian plant arrived in the 1990s, and to date, NASA has received about 70 to 90 pounds of plutonium. A few pounds of Stalin’s finest plutonium-238 hitched a ride to Mars on the back of Curiosity.

Even this supply is now running out. Russia has gotten out of the bomb-making business as well, and it’s running low on plutonium-238. NASA is looking for new ways of making it, and this year, it asked Congress for $10 million to investigate the possibility of restarting production at smaller research reactors near Savannah River and in Idaho. This time around, scientists say they’ll do things differently. They’ll be working with smaller quantities in more modern facilities, they’re going to try to find cleaner ways to chemically separate the fuel, and they’ll be subject to environmental regulations — something the old bomb factories avoided by virtue of national security. The circumstances may have changed, but the chemistry and physics haven’t: Making plutonium-238 is still a very sloppy, very radioactive business, and setting up the new facilities won’t be cheap. A review by the National Academies of Science estimates that restarting production would cost hundreds of millions of dollars.

There’s nothing wrong with oooh-ing and aaah-ing over Curiosity’s photos. The project is an incredible achievement, and the science it produces will be amazing. But remember this, too: That little rover on Mars has left a big mess back here on Earth.

Geoff Brumfiel is a reporter based in London.