Armageddon delayed by at least a century... this time

# Armageddon delayed by at least a century... this time

The entire universe in blog form
April 29 2010 10:51 AM

# Armageddon delayed by at least a century... this time

What does a one-in-ten-million chance of apocalypse look like? Well, it used to look like this:

Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!

That is asteroid 2005 YU55, a near-Earth object (or NEO) that also happens to be a PHA, or potentially hazardous asteroid. It has an orbit which intersects the Earth, which means that someday it could possibly hit us.

Now before you panic -- and I'll make this clear: DON'T PANIC -- that doesn't mean you'll wake up tomorrow to see flaming death streaking across the sky. Think of it this way: when you walk to the local convenience store to get a squishy, you have to cross the street. The path you take intersects the street, but as long as you don't try to occupy the same spot as a moving car, you won't get hit. Same with PHAs: their orbits cross the Earth's orbit, but space is big. As long as the Earth and the asteroid aren't at the same place at the same time, we're OK. Since we don't know the orbits of these objects perfectly, we assign a probability they will hit us over some period of time. Up until recently, YU55's chance of hitting us over the next century was calculated to be about 1 in 10,000,000, which is reasonably close enough to 0 for me. However, it's always good to get better data. In this case, very good: new observations have eliminated the chance that YU55 will ruin our day for at least a century to come.

YU55 was observed with the monster 300 meter (1000 foot) Arecibo radio telescope in Puerto Rico. Arecibo can send little radar pings into space, aimed at an asteroid. The pings reflect off the rock, come back to Earth, and the timing of each one can be logged. This tells us how far away the asteroid is, how big it is, and even (by carefully measuring the different arrival times of the pings back on Earth) the shape of the asteroid.

If this sounds familiar, that's because this is how dolphins and bats sense their environment. They use sound, not light, but the principle is the same. So what did Arecibo tell us when it dolphinated YU55?