Here's a little Christmas present to the people of the Earth from NASA: Near-Earth asteroid 2011 AG5, which initially set off some alarms about a potential impact in the year 2040, has just been removed from their Earth Impact Risks list.
When astronomers discovered 2011 AG5 on January 8th last year, they used subsequent observations of the asteroid to plot its path around the Sun. With a period of only about 1.7 years, the asteroid moved quickly enough that they were able to put together a good first estimate of its orbit, but with a wide margin of error — what they called the "region of uncertainty". The alarm was raised when their simulations showed that Earth was going to pass through that region of uncertainty on February 8th, 2040, making an impact with the asteroid a possibility.
The probability of the impact was calculated to be only one in 500, which ranked it as a "1" on the Torino Impact Hazard Scale, meaning that there was very little chance of impact. However, when we're talking about the chances of a 140 metre-wide hunk of rock slamming into the Earth, causing the equivalent of a 100 megaton bomb exploding at whatever unfortunate location takes the hit, it is worth it to investigate any possibility of impact. Some even came up with potential deflection missions, should the threat be confirmed.
Astronomers Dave Tholen, Marco Micheli, Richard Wainscoat and Garrett Elliott, all from the University of Hawaii, answered the call for more observations by tracking the asteroid using both the Gemini 8-metre telescope and the University of Hawaii 2.2-metre telescope, both atop Mauna Kea, Hawaii. The images they captured in October of this year added more data to 2011 AG5's orbit, narrowing the region of uncertainty significantly, and prompting NASA officials to sound the "all clear" and remove the asteroid from their Earth Impact Risks List.
(NASA image of 2011 AG5's orbit)
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