![]() Given the asteroid’s distance and brightness in those 2009 observations, they calculated it was small, probably 10 meters in size. Out of caution, as usual, astronomers knew the prediction was extremely rough but kept this rock in mind. Think of it this way: That’s a 99.975% chance it would miss. Still, extrapolating its motion showed that on there was a 1 in 4,000 chance it would hit Earth. But if you keep watching it you’ll be able to see its trajectory much better.Īt the time, 2009 JF1 was very faint and was only able to be tracked for roughly 30 hours, not nearly enough to get a good grip on where it would be in the future. Now, predict where the ball will be when it lands. The analogy I like is if you're an outfielder in a baseball game, and as soon as the batter hits the ball you close your eyes. Small uncertainties in the position early on add up to big ones later. That’s a cause for concern though not necessarily alarm it’s difficult to get a very accurate orbital calculation over so short a time frame: As I've written before, when an asteroid is first discovered, the orbit calculated for it is pretty fuzzy, because we don't have a long enough arc to really be able to predict where it will be in the future. ![]() The initial calculations showed that 2009 JF1’s orbit came very close to Earth, within a mere 200,000 kilometers or so, less than half the distance to the Moon. Credit: Earth: ESA/Rosetta asteroid Mathilde: NASA/NEAR Photo:Įarth: ESA/Rosetta asteroid Mathilde: NASA/NEARĪsteroids appear as a dot moving from frame to frame as images are taken over the course of a night, and using its position versus time it’s possible to calculate the shape of its orbit. Illustration of a near-Earth asteroid, created using actual space images of Earth and the asteroid Mathilde. ![]()
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