The red phone on my desk went off again, flashing and beeping urgently. What was it this time? Another super-villain escaped from prison, threatening the safety of Oakland City again? I pick up the phone to find out. Ah, it was Apophis again, back in the public eye and causing concern for one of our citizens.
This has been a dramatization.
At Chabot Space & Science Center, I'm the one who answers the science help line, which is why I keep my cape and cowl close at hand.
Ah, Apophis, that thousand-foot chuck of rock plotting to buzz the Earth. The citizen on the phone has called about Apophis before, so I figured it was time to back up my response with the word from a resident asteroid expert, Gerald, one of Chabot's asteroid tracking team—like Alfred passing the phone to Bruce.
Gerald's report on Apophis: After 3.8 years of observations, we project that Apophis will pass by (and miss) the Earth by about 23,600 miles on April 13 (yeah—Friday the 13th) 2029 (in case you want to plan a party). Then, Apophis will revisit the Earth's vicinity on April 13th (not a Friday) 2036. And here's the meat of the deal with Apophis: if its trajectory on the 2029 flyby is anywhere near what is predicted, then there is no chance at all that it will hit us in 2036. There is only a small chance that within the range of uncertainty the 2029 passage will aim Apophis for a 2036 impact with Earth--but the probability of that are calculated at less than 0.002%. That's roughly the same probability as drawing a straight flush right off the top of the deck (to you non-poker-players, the odds of that are about 72,000 to 1).
Though astronomers are planning to observe Apophis next year using the giant radio telescope at Arecibo to give us a more refined impact probability for the 2036 passage (still 24 years out!), the consensus among scientists is that the refinement should further diffuse concerns, not raise them.
We know of about 1300 asteroids of significant size that can pass close to Earth, and estimate there may be up to two or three times as many that we haven't spotted yet, but at this time there are no major threats projected to occur in the foreseeable future.
In 2013 there are two notable asteroid flybys of Earth. On February 15 a rock of the 200-foot size, called 2012 DA14, will cross our evening skies and pass within 17,760 miles of us, well within the fleet geosynchronous satellites that ring the Earth. It won't , repeat, won't hit us at this time.
Later in 2013, a much bigger asteroid, called 2005 WK4, will pass by at a much greater distance. The object is somewhere between 950 and 1420 feet across, but will pass no closer than about 2 million miles, on August 9th. Again, there is zero chance that it will hit us.
With all of those rocks flying around that can cross Earth's orbit and therefore be a impact threat, what are the odds of one hitting us? Generally speaking, an object of the several hundred foot size hits Earth every few thousand years. In fact one did so in 1908, over Siberia.
More sizeable objects, between 600 and 1600 feet across, strike us about every 100,000 years. And those really big ones, like the 6-mile diameter asteroid that struck the tip of the Yucatan 65 million years ago, the impact that is thought to have led to the demise of the dinosaurs, run into us about every 100 million years.
These are really steep odds if you're playing poker, but in this case that's a good thing.