Asteroid Scare

(This 741st Buffalo Sunday News column was first published on June 12, 2005.)

Last December a quarter-mile diameter asteroid hurtling through space was assigned 36:1 odds of slamming into the Earth on April 13, 2029 -- possibly a very unlucky Friday.

If that doesn't sound like much of a chance, recall that in early May Giacomo beat 50:1 odds to win the Kentucky Derby.

An aside here about odds may be appropriate as they are often misunderstood. First, usually as they are here, odds are quoted against the event happening. Second, to convert odds a:b to the chance of the event happening, calculate b/(a+b). Thus, those odds of 36:1 equate to a chance of 1/37 or 2.7% that the asteroid would strike the Earth.

Like many scientists I consider that projection frightening. If it occurred, the event would be apocalyptic, the power generated nearly the equivalent of 1000 megatons of TNT. That is 80,000 times the power of the bombs that destroyed Hiroshima and Nagasaki during World War II.

Fortunately, the chance of our colliding with that asteroid, named by astronomers 2004 MN4, was soon downgraded to 300:1 and more recently to 10,000:1. But even those odds are comparable to the odds of your being in an automobile accident on any given day.

Those odds are calculated by measuring devices that have become so accurate that astronomers are able to fix the position of objects in space even when they are millions of miles away. A series of such fixes give them the route of such space debris as it, like Earth, hurtles in an elliptical path around the sun.

Some astronomers today are specializing in such measurements and they have determined the orbits of hundreds of so-called NEOs, for Near Earth Objects. Asteroid 2004 MN4 remains, however, the most threatening such object identified until now.

There is still more to this story. A few days ago former Apollo astronaut Rusty Schweikart testified before Congress about an additional problem that 2004 MN4 poses. Even if it misses the Earth in 2029, it will pass very close, closer in fact than some of the satellites we have launched to provide us with communication and positioning data. The Earth's gravity at that time will deflect the asteroid's orbit and could cause it to hit us when our paths cross again seven years later.

The possible scenario Schweikart poses, based on further calculations, has the asteroid plunging into the Pacific about 1800 miles from southern California and creating a tsunami comparable to the Indian Ocean tsunami last December and destroying much of our west coast. There would be good news and bad news associated with such a catastrophe. The good news is that loss of life would be minimal because the forewarning would allow Californians to retreat from the shoreline. The bad news is the half-trillion dollars of devastation they would find upon their return.

Schweikart makes a good point when he calls for Congressional action now to prepare for even such a remote possibility. We should be testing engineering responses to such collisions, he tells us. In support of this he points out that any mission to deflect this asteroid after 2029 will require 100,000 times the amount of energy than it would before that first near approach.

There is a reason for this. To come back and hit us in 2036, the asteroid would have to bounce off our gravity field just right -- or just wrong from our point of view. That bull's-eye turns out to be just a half mile across, only twice the diameter of the asteroid itself. It would take very little energy to deflect it from that tiny zone. Once it hit that zone, however, the asteroid's future course would be determined and the Earth itself would serve as its much larger target the next time around.

Space engineers have come up with several ways of deflecting such an object. One of them would be to set off an atomic bomb on one side of the asteroid. But whatever the response, years of planning and rocket construction are required.

Now is the time, Schweikart says, to begin this effort. It will pay off not only for 2004 MN4, but for other asteroids and comets that may threaten us in the future.-- Gerry Rising