The big boom over Chelyabinsk on February 15 also produced a wave of sound thousands of times lower than a piano’s middle C — far below the range of human hearing, according to the international agency that watches for nuclear bomb tests. The Comprehensive Test Ban Treaty Organization said that sound wave showed up on sensors from Greenland to Antarctica, making it the largest ever detected by its network.

Scientists then used that wave to calculate the size of the small asteroid that plunged to Earth, said Margaret Campbell-Brown, an astronomer at Canada’s University of Western Ontario.

The duration of the wave — about 32 seconds — let scientists estimate the energy of the blast at between 450 and 500 kilotons, the size of about 30 early nuclear bombs.