Helium is the second-most abundant element in the known universe, but it’s hard to capture on Earth because of how easily it floats out of the atmosphere and into space.

Oil companies harvest helium trapped deep beneath the Earth’s surface, in natural gas chambers. Radioactive decay causes uranium rock to disperse helium into natural gas chambers over millions of years. It’s a slow process, and finding the helium can be even more challenging.

Almost every known helium reserve on the planet was discovered by accident, and the helium was merely a byproduct of natural gas harvesting.