The meteor that broke up above the Russian town of Chelyabinsk on Friday, Feb. 15 was bigger and heavier —much heavier— than we first thought.

NASA scientists originally estimated that the meteor was 50 feet wide with a mass of about 10 tons. They estimated that it released close to 500 kilotons of energy when it broke up.

Another estimate was released later Friday night. Using infrasound data from around the world, NASA came up with a new estimate, claiming the meteorite weighed more than 10 tons. Way more than 10 tons. The new estimate puts the space rock at a heavyweight 10,000 tons.

Why the discrepancy? There's a lot of stuff out in the empty void of space. And while it's easier to track the big stuff, like the 150-foot, 200,000 ton meteor 2012DA14 that did a near Earth fly-by, also on Friday, the smaller stuff makes for a challenge.

"If you think about objects the size of the one that came into Russia, you're probably looking at 100 million up there. Of those likely to intersect Earth, there's less, maybe 100,000," K.T. Ramesh, director of the Hopkins Extreme Materials Institute and a mechanical engineering professor at Johns Hopkins, told Fox News. "In general, we're pretty good at seeing things that are 1 kilometer and up in diameter, and have trouble seeing things that are less than 100 meters in diameter. The big problem is knowing where they are — once you know where to look, you can find even the smaller objects."

The surprise nature of the meteorite only made its size and mass harder to guess. "A good analogy is finding a few pennies scattered over an acre of dirt," said Ramesh. "If you know where to look, you have no trouble seeing them. But if you just look over the whole field, your chance of finding a penny is pretty small."