(CNN) -- The meteor that exploded over the steppes of southwestern Russia sent a low-frequency rumble bouncing through the Earth, giving scientists new clues about the biggest cosmic intruder in a century.
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
From there, Brown said, they could calculate the size of the fireball; and using an estimate of the meteor's speed from the numerous dashboard and mobile-phone cameras that captured the scene, it was "first-year physics" to figure out the approximate size and weight, she said.
The latest estimate is that the Chelyabinsk meteor was about 56 feet (17 meters) across, weighed more than 7,000 tons and was moving about 18 kilometers per second (40,000 mph) when it blew apart, she said.
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"In terms of things we have observed, this is the largest since Tunguska," Brown said, referring to the suspected meteor that flattened a Siberian forest in 1908.
The nuclear test monitors pick up "infrasound", or low frequency, waves from about 20 meteors a year -- "if conditions are right, perhaps as small as a pea," she said.