near-earth asteroids
What are the chances that an asteroid is headed our way?
Calculating the probability of an asteroid impact can help protect us from these cosmic wanderers.(click to enlarge) ©AMNH
How likely is it that something from outer space big enough to cause real trouble will smash into Earth? While we can't know for certain, we can get a sense of the odds by calculating the probability: the likelihood that such an event will take place. The statistical answer is one in a million in any given year. This figure is based on estimating the total number of asteroids and comets of a certain mass and calculating the likelihood of any of them hitting something the size and gravity of our planet.
As we inventory the asteroids and comets that could pose a threat, what really matters is the likelihood of any specific one actually hitting us. The most important variable here is how long astronomers have been watching the object. A newly discovered "Near-Earth Object" is likely to be assigned a higher probability of hitting Earth because the margin for error is huge. But as time passes — even as little as a few days — the impact probability shrinks drastically as more observations generate more accurate predictions. As Jon Giorgini, an analyst at NASA's Jet Propulsion Laboratory, points out, lots of possibilities never occur. "It's possible I will be on top of Mount Everest 60 days from now at 12:01am, but I'm not predicting it," he writes. "And there will come a point when my being on Mount Everest at some instant can be positively excluded ('That's impossible!')."
Small though it may be, there's always some chance that an asteroid or comet will strike Earth. But calculated probabilities show just how rare that is.
Asteroid Impacts: How Do They Stack Up?
| 1:100,000,000 | Odds of an asteroid impact causing global disaster in any given year |
| 1:95,980,407 | Odds of dying from a venomous snake or lizard bite in any given year |
| 1:4,362,746 | Odds of dying from a lightning strike in any given year |
| 1:3,529,526 | Odds of winning Lotto from a two-draw slip |
| 1:2,598,960 | Odds of drawing a royal flush in spades in a five-card poker draw |
| 1:100,000 | Odds of an asteroid impact causing regional disaster in any given year |
| 1:91,149 | Odds of dying in a fire in any given year |
| 1:541 | Odds of having triplets if you give birth |
| 1:10 | Odds that astronomers are actually aware of an asteroid larger than 1/2 mile in diameter |
| 1:6 | Odds of a sunny day in Seattle |
| Source: Science Bulletins (http://sciencebulletins.amnh.org/astro/f/nea.20050504/essays/56_1.php) |
