Asteroid 2005-YU55 whizzed past us on November 8 and is now zipping back into the depths of space. Measuring more than a thousand feet in diameter, it passed within 200,000 miles of Earth, a bit closer to us than the moon and just a hair’s breadth in astronomical terms. What if it had slammed into us?
If you find this sort of potentially real-life horror story as morbidly fascinating as I do, then you’d probably enjoy using the virtual "Catastrophe Calculator" to explore it in dark detail. More formally known as the Earth Impact Effects Program, it’s a free web-based tool for estimating the havoc that would be wrought by a theoretical asteroid or comet impact. Hosted by Imperial College London and Purdue University, the Calculator asks you to enter information about key features such as speed, composition, and angle of attack, and then it tells you what would happen if the object struck within a given distance of you.
Inputting a typical asteroid velocity of 17 km per second, a stony composition (the makeup of the 2005-YU55 asteroid), and a slanting 45 degree crash path yields a grim outcome. If you were to watch from the edge of a forest 10 miles away, you could see the asteroid blast a hole 4 miles wide and 1,670 feet deep into solid bedrock, producing a brilliant fireball three miles wide that would leave a puddle of molted stone 15 feet deep at the bottom of the crater. A little less than a minute later, a super-heated shock wave would slam into you, ignite your clothing, and set the woods around you ablaze after knocking you and most of the trees over. Ten seconds after that, heavy blocks of shattered rock averaging 16 feet across would rain down on you, burying what’s left of you and your surroundings.
If 2005-YU55 hit the ocean instead, a massive tsunami wave would result. If the asteroid landed in 1,000 feet of water, it would dig a pit three miles wide into the seafloor and push a huge, spreading wave crest more than 500 feet high. If instead the water were a mile deep, as in mid-ocean, the tsunami would be nearly 1,000 feet tall.
A newer "Damage Map Version" of the program also uses Google Earth to show how wide an area around a major city the shock wave, crater, and other effects would cover. The crater from a 2005-YU55 strike on the southern end of Central Park would consume the entire mid-section of Manhattan. Debris would rain down over the entire western half of Long Island, and the air blast would be felt as far away as Philadelphia and Hartford.
According to the calculator, asteroids this large have struck the Earth once every 100,000 years or so during the last 4 billion years. That’s small comfort in the long run, though; our long-suffering planet is pocked with the scars of earlier impacts, some of them large enough to cause mass extinctions in the distant past.
2005-YU55 is out of the picture for the next century or more, but another close shave with a bigger, meaner asteroid is slated for June 2028. Dubbed (153814) 2001 WN5, it’s between 2,000 and 3,000 feet wide, and is expected to come close enough to see with binoculars. I’ll leave it to you and the calculator to figure out what a collision with that one might mean. Try it—if you dare.