Space junk is that excess material floating beyond the atmosphere. Composed mainly of satellites and rocket stages, it’s the leftover refuse of human spaceflight and Gravity rehearsals. While space junk usually hangs out in the Earth’s orbit like a plastic bag fluttering in the wind, chunks sometimes come screaming back to the ground.

Enter the case of some mysterious “space balls” that crash-landed in Vietnam on January 2. The three balls — varying in size between 250 grams, six kilograms and 35-45 kilograms — could be leftover compressed air-tanks, ostensibly produced in Russia for a rocket, investigators surmised. The large, spherical objects could also be the remnants of a failed satellite launch.

Hey, don't mess around with the space balls

This is all according to Professor Nguyen Khoa Son, who works for Vietnam’s State Space Science and Technology Program. He told VietnamNet Bridge that many satellites enter the earth’s atmosphere in a safe and controlled environment, and usually burn and disintegrate before they reach the ground. Other large-scale satellites, Khoa Son warned, do not interact with our planet in such an innocuous manner.

The three black spheres — which bear a strong resemblance to cannon balls — have been seized by the Vietnamese Air Defense Arms, and are being examined by the country’s Ministry of Defense. No one was hurt, although residents did report what sounded like thunder when the orbs entered the atmosphere. One sphere was reported to have bounced off a person’s roof, while another landed pleasantly in a residential garden.

Photos via VTV3, VietnamNet Bridge