Target: Earth!

One of the best arguments, perhaps THE best, for a human presence in space is the certainty that there will someday be a civilization-killing asteroid or comet headed our way. It has happened in the past—just ask the dinosaurs—and it will happen again. If we haven’t developed the ability to protect ourselves from such a danger by then, we probably deserve our fate.

Contrary to what many people assume and popular movies depict, the solution is not to plant a nuclear weapon and blow the thing apart. Where would the fragments go? Most of them would continue right along the same path that intersects the Earth, and we would have traded death by an artillery shell for death by shotgun pellets. The far better path is to apply a gentle nudge while the object is far away from the Earth, just enough to make it miss. The farther out we can do this, the more gentle that nudge can be.

This means there are two parts to a protective scheme for the Earth: detection and mitigation. NASA has actually been directed by Congress to catalog 90% of potentially hazardous asteroids by 2020, and since this 2005 mandate, much progress toward that goal of detection has been achieved. A few weeks ago NASA announced that they had achieved the 90% goal for the larger asteroids (larger than 1000 meters in diameter). The graph below shows the cumulative total of all near-Earth asteroids discovered, as well as the total for those larger than one kilometer. A little thought about the shape of these curves will convince you that most of the recent discoveries have been of objects smaller than one kilometer.

Detecting objects this small requires big telescopes. The objects are visible only by reflected sunlight, and most asteroids are rather dark. There are several dedicated programs using large, wide-angle instruments that scan the sky nightly. It will take a while to get to the 90% level for all such objects, however. Why not 100%? The number of objects increases as the size gets smaller, sort of like the distribution of boulders, rocks, pebbles and sand on a beach: a few boulders, more rocks, even more pebbles, and LOTS of grains of sand. We’ve found the boulders and rocks. Now we’re looking for the pebbles and grains of sand.

But don’t think that a small object can’t be dangerous. Is a bullet that only weighs a few ounces dangerous? Not if you drop it on your foot. But put it into a gun, give it a velocity of 400 meters per second, and you don’t really want to get in its way. Even a relatively small object traveling at a typical speed of 40 kilometers per second relative to the Earth can have an impact equivalent to thousands of Hiroshima-sized atomic bombs.

Asteroid 2005 YU55

Which brings us to Asteroid 2005 YU55 and its rendezvous with the Earth on November 8th. No, we aren’t going to be hit. But it’s going to be a very near miss. The asteroid will pass between the Earth and the moon, and it will be going FAST. Take a look at the animation below (click on it):

The asteroid is approximately 400 meters in diameter. Were it to collide with the Earth, the impact would be around 10,000 times as energetic as a standard Cold War-era hydrogen bomb.

Can you see it as it passes? Only with a small telescope, and it will be a difficult object to catch even then. It will be at its brightest on the evening of November 8th, and a good time to catch it will be between 9 and 10 p.m. EST. (We will have just come off daylight saving time the weekend before.) Unfortunately, there will be a nearly full moon nearby, which makes the task harder. The moon really is an astronomer’s worst enemy sometimes!

Where to look? I spent a fruitless hour looking for online finder charts, with no success whatever. So here is my crude attempt to give you some idea of where it will be—in the bull’s eye below. Realize that it will be moving FAST. By midnight in the Eastern time zone, it will have moved inside the square of Pegasus that lies above it in this image. The moon and Jupiter (yellow dot) are above and to the left of the square of Pegasus. The cardinal directions on the horizon line tell you which way to look.

If you have at least a six-inch scope, you may have a shot at it. For those used to using these coordinates, it will travel from approximately RA 21h 45m Dec +15° at 9 p.m. EST, to RA 22h 15m Dec +16° 30’ at 10 p.m. Happy hunting!

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