At any given moment, as many as 10 million wild jets of solar material burst from the sun’s surface. They erupt as fast as 60 miles per second, and can reach lengths of 6,000 miles before collapsing. These are spicules, and despite their grass-like abundance, scientists didn’t understand how they form. Now, for the first time, a computer simulation—so detailed it took a full year to run—shows how spicules form, helping scientists understand how spicules can break free of the sun’s surface and surge upward so quickly.