Two mysterious, translucent glass balls have been found on the far side of the moon and scientists think they know how they got there. China's Yutu-2 rover sent back images of the objects.
Glass is formed when silicates, such as beach sand, reach intensely hot temperatures and become liquid. While glass balls have been found on the lunar surface before, the translucence of these new ones is what makes them unique.
Some glass balls as large as 40 millimeters across were found during the Apollo 16 mission in the Descartes Highlands and were brought back to Earth. But they didn't have that translucence.
How did it happen? Scientists suggest they were made either by a volcanic eruption in the moon's past or a meteorite impact, the latter of which is the more likely explanation, according to Science Alert. They were found near fresh impact craters.
It's also possible they were already buried below the moon surface and that meteorite impacts exposed them.
Those findings are expected in a Feb. 26 publishing of the journal Science Bulletin.
"Impact glasses on the Moon are formed by cooling of impact melt and/or condensation of impact vapor, and impact glass spherules have rotational shapes, smooth surfaces, and largely clast-free interiors," a preview of the findings reads.
That could make the spheres the lunar equivalent of a phenomenon seen on Earth called Tektites. According to the Australian Museum, Tektites are "small, pebble-like glassy objects of Earth material that have been melted by meteorite impact, splashed up into our atmosphere, and fallen to Earth again under gravity."