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Grains specifically from the Kuiper Belt would have wandered 10 million years to reach Earth’s atmosphere, the researchers calculated. That’s “pretty solid evidence that we’re collecting Kuiper Belt dust right here,” Keller says.

Four of the dust grains contained minerals that had to have formed through interactions with liquid water. That’s surprising. The Kuiper Belt is thought to be too cold for water to be liquid.

“Many of these particles, if they in fact are from the Kuiper Belt, tell you that some of the minerals in Kuiper Belt objects formed in the presence of liquid water,” Keller says. That water probably came from collisions between Kuiper Belt objects that produced enough heat to melt ice, he says.

“I think it’s incredible if Lindsay Keller has shown that he has pieces of Kuiper Belt dust in his lab,” says Carey Lisse. He is a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. But, he adds, researchers must do more work to confirm that the dust really came from the Kuiper Belt. The dust could have been just sitting on an asteroid for millions of years. “Lindsay needs to get a lot more samples,” Lisse says. “But I do think he’s on to something.”

Lisse works on NASA’s New Horizons mission. That spacecraft found plenty of dust in the outer solar system. The spacecraft measured the dust’s abundance near Pluto when it flew past the dwarf planet in 2015. Based on those results, Lisse finds it unsurprising that some of that dust has made its way to Earth. But it is “really cool,” he says. “We can actually try to figure out what the Kuiper Belt is made of.”