I really don't like coincidences in science. Reports are asteroids of this size getting this close occur about once in 30 years. And meteors the size of the Russian one enter our atmosphere about similar frequency. But the problem is their both occurring in the same 24 hour period. If you imagine the asteroid arriving on a particular day, the question to ask is what is the probability of the Russian meteor arriving on that same day? Once in 30 years, and then 365 days in a year, means the chance of this happening is like 1 in 10,000. That's disturbingly unlikely.
On the other hand if this really is just coincidence, then it should be kept in mind that chances this low have been quoted in regards to large asteroids impacting Earth in our lifetime.
An article by a Yale astronomer:
A meteor and asteroid: 1 in 100 million odds.
By Meg Urry, Special to CNN
updated 8:16 PM EST, Mon February 18, 2013
http://www.cnn.com/2013/02/16/opinion/urry-meteor-asteroid/index.html
She states the two have very different orbits so they should be unrelated, but acknowledges that the very low probability of their both occurring so close to each other in time is puzzling.
In view of the very real dangers that would arise IF it is the case they are related I think we should investigate some possible ways this could occur. What I mean by this is cases where we assume asteroids that make close approaches but do not impact, and therefore offer no threat,
still could have associated fragments that do impact.
One way is mentioned in the comment section to this NASA blog which shows the different orbits of the asteroid and the meteor:
How Do We Know the Russian Meteor and 2012 DA14 Aren't Related?
Posted on Feb 16, 2013 11:37:14 AM | William Cooke | 25 Comments |
http://blogs.nasa.gov/cm/blog/Watch the Skies/posts/post_1361037562855.html
First though, note there are many ways a fragment could be separated from the main asteroid. For instance some asteroids are "rubble piles", loosely held together by gravity. In this case collisions among the individual fragments could send a fragment away from the main asteroid body.
Another is the obvious way of a collision with another asteroid or meteor.
Still another would be outgassing of volatiles that provides another force to separate a fragment from the asteroid.
Then once the fragment is separated from the asteroid, over time, since it was given some initial boost away and the asteroid gravity is so small, it will travel further and further away from the asteroid, though still in the same or close orbit. But the key point is depending on the direction the fragment is sent, once the asteroid comes around to the Earth or Moon or other planet on a close approach, that fragment could be much closer to that large gravitating body than the asteroid and therefore be sent on a different orbit.
Then on subsequent orbits it could impact the gravitating body. Indeed it could even be captured by the gravitating body, such as the Earth, depending on the speed it is traveling with respect to the body. For instance asteroid 2012 DA14 was traveling at 18,641 mph, about 8.3 km/s on closest approach. At the distance it passed the Earth at 17,000 miles this is greater than escape velocity. But it's less than escape velocity at the Earth's surface. So a fragment that happened to be closer in to us on that closest approach could have been captured.
Bob Clark
