I must have left my manners in the hotel room upon coming back from vacation because I completely forgot to thank Andy for manning the ship while I was gone. He was kind enough to repost all of the stuff I had written for the last week and he provided the question for last Wednesday's science post as well. He's a good laddie that Andy is. So thanks mate. There's a pint in it for ye once we meet up again.
On to this week's question, provided by Aaron. He asks:
It has not been asked before, and this is an excellent question. Nice work son.
OK, so if it hasn’t been asked before, I’d like to know what the chances are of an ‘end of days’ asteroid striking the earth in our lifetime?
The answer all depends on just who's days are going to be ending. If it's all of our days, it's pretty unlikely, if it's just your days, it's slightly more likely. That's not to say that Aaron has some crazy, whackjob stalkeroid out there sitting in a skeezy gray van circling Aaron's picture with a black marker while rocking back in forth in the driver's seat, more that we could very well see an asteroid impact in our lifetime, just not one that will wipe out all life on the planet. Some life, possibly, just not all life.
The Earth is no stranger to getting pounded on by space rocks, as impact craters exist all over our fair world in various places such as the Yucatan Peninsula, Siberia, the Canadian High Arctic and here in the good old US of A. The impact in the Yucatan Peninsula is thought, by some, to be the catalyst for the extinction of the dinosaurs, and about 70% of all species on the planet at the time. Sure, we're a heck of a lot smaller than the dinosaurs, but not small enough to weather such an impact and emerge unscathed.
On the other side of the spectrum, we have the Tunguska Fireball. In 1908, in the Tunguska region of Siberia, a massive explosion occurred about 6 - 8 km above the surface of the earth. The resulting explosion caused shockwaves that could be measured as far away as Germany, incinerated trees and herds of reindeer and produced a fireball that could be seen and felt from 60 km away. The prominant theory is that some sort of space rock, be it a comet or a meteorite, detonated in the atmosphere. The sides are pretty well split between comet and meteorite, however what they can agree on is that a) it was from space, b) it was a rock and c) it weighed about 100,000 tons. Replace "remote section of Siberia" with "New York City" and you can see why a space rock impact could very well end some days, but not all our days. Oh sure, we'd all have a bad day in one way or another if a major city was taken out by a passing space rock, but some of us would have a worse day than others.
So, how can we assess the threat that looms above us in space? Thankfully, we have science to help us. The fine folks at Nasa currently use what's called the Torino Scale (developed by a one Richard P. Binzel, MIT) which rates Near Earth Objects (NEO's) from a scale of 1 - 10. A 1 means that there's something out there that could, some day, possibly strike the Earth, however subsequent readings should reclassify the object as harmless, to a 10 which means that a mass level extinction object is on its way and a collision is assured. The Torino scale isn't perfect, as it tends to get folks all riled up, thinking they're going ot die in a storm of hellfire, and was reworded in 2005 to not sound quite so dire. Some folks advocate the ditching of the Torino Scale altogether and replacing it with some other scale, such as the Palermo Impact Hazard Scale, which is a logarithmic scale used to assess threats to the Earth. The Palermo Scale isn't as easy to communicate to the public (logarithms are funny that way) and doesn't have the informative color coding we as Americans have come to rely on. As any post 9-11 American can attest to, our media loves themselves some color coded threat levels.
From the Torino Scale we have 3 levels of "Certain Collision". An 8 means something is going to hit the earth and do some localized damage, a la what happened in Tunguska. This happens every 50 to several 100 years. A 9 wouldn't kill us all off but would really do some damage on land, or cause a massive tsunami at sea and happens every 10,000 to 100,000 years. A 10 is the big one, causing you to either perish or emerge as Lord of the Roaches. These happen once per every 100,000 years at the most frequent, but probably a hell of a lot less often. Whew.
Currently there are 13 NEO's observed by NASA in the past 60 days, two of which are rated with a rating of 1. To give you an idea as to how quickly some of these ratings are downgraded, when I originally researched this info on Monday, May 22nd, one of these objects had a rating of 2. Of the two rated objects, one has an impact year of 2102, and one has an impact year range of 2036 - 2069. Again, with a rating of 1, it's pretty much assured that neither NEO will impact the earth, however if it did, you're looking at an impact possibly 63 years from now.By then, I'll have had a pretty good run, being 97 years old and most likely would welcome the opportunity for an obituary that read "Brandon Cackowski-Schnell, 97, Nailed by Asteroid".
So, given the fact that we're currently not tracking anything capable of doing anything but possibly causing media scares, and given that about 80% of the Earth's surface is uninhabited, I'd say that the odds of you witnessing an asteroid impact that causes massive amounts of casualties is pretty unlikely. While it's true that even an ocean impact could cause a tsunami that could do a large amount of damage to coastal cities, there's a hell of a lot more ocean that's no where near coasts than there is beachfront waters. Bottom line is that yes, Aaron, you have to mow the lawn this weekend. Find some other reason to blame your procrastination on.
Much like how people used to really win on MTV, people really get their questions answered here at SuburbanJoe, so keep 'em coming.
Near Earth Object Program, NASA - Current Impact Risks
Near Earth Object Program, NASA - The Torino Impact Hazard Scale
Wikipedia - Torino Scale
The Straight Dope - "What caused the massive 1908 explosion in Tunguska, Siberia?", Cecil Adams, Feb. 28, 2003
Astrobiology.com - Contemplating Craters