That was the most sensational headline I could come up with. However, an article in the August issue of Scientific American explains that an asteroid named Bennu poses just such a possibility. Bennu is large enough, about a third of a mile in diameter, to do enough damage to essentially destroy civilization as we know it if it were to strike the Earth. The asteroid circles the sun every 1.2 years, and has an elliptical orbit that takes it close to the Earth every six years. Because it comes relatively close to our planet so often, it is studied more than any other asteroid. Its path away from the Earth takes it as far as 210 million miles away, and as close as … that’s the crucial point … even closer than our moon in the year 2035, only 126,000 miles. No sweat, you say. Plenty far away. But wait; this distance has been changing, and has shifted by about 100,000 miles just in the past sixteen years!
The reason is something called the Yarkovsky effect, which has to do with the way the asteroid is rotating and the way the sun heats it when it gets closest. Bottom line, in the year 2025 Bennu will come near enough that it is possible (a long shot, but feasible) that its path will hit a “sweet spot,” or what’s called a “key hole” such that the Yarkovsky effect will put it on a collision path with the Earth in its approaches between the years 2175 and 2196. None of us will be around then, but it’s an unpleasant possibility for our descendants. In that event, a representative population of the Earth would have to be evacuated to another location for at least a long time (how would you like to have to make that decision?) before resettling here with what's left, or the asteroid would need to be deflected somehow from its course.
In order to get more information on Bennu, a space probe will be launched this year (September, 2016) to sample its surface and gain more information on its composition. The probe is planned to land on the asteroid in 2018 after a two year flight, circle the object to obtain information regarding a landing site, land for samples in 2021, and blast off after an extremely short time to return to Earth over a two-and-a-half year journey by late 2023.
The chances of this thing hitting the “key hole” are not great, in fact only one-in-ten-thousand in 2025, but in the period 2175-2196, the odds are frightening at one-in-2,700! Tighten your seat belts and be ready for more information on Bennu.
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