Meteorite hits Russia - 2/15/2013

A typical meteorite.

By now everyone has certainly heard about the Meteorite that struck Russia.  The news outlets everywhere blew up with the story, and YouTube has seen its share of videos on the topic.  So what really happened over in Russia, how can they prove it, and what does it mean to you and me?

First and foremost the meteorite did not make a single impact.  It in fact broke apart in our atmosphere (about 10 to 15 mi above the surface), scattering its debris across Chelyabinsk Oblast Russia.  The force released by the break up is estimated between 20 and 30 times stronger than the atomic bomb!  The (now named) Chelyabinsk Meteor  is considered the largest known object to have entered the Earth's Atmosphere  in over 100 years.  It is also believed to have caused the most injuries (since recorded history of course!)



So what is a meteorite? 
A meteorite is basically space rock.  The rock gets really hot as it enters the atmosphere of Earth, and that is what gives it the glowing colors you see.  Meteorites come into contact with our atmosphere all the time, they are usually very small so they burn away before they hit the ground.  We typically call these "shooting stars".  But every once in a while, you will have a rock so large (like this event) that it does not completely get destroyed in the atmosphere and collides with the Earth itself.  Some of the more recent meteorite impacts can be found here.

We know meteorites have come in contact with the Earth before.  In fact we have a formula that can predict just that!

Impact Crater

How can we prove it?
The best evidence of an impact is obviously the impact crater.  However, when you deal with a planet like Earth it constantly changes.  Earth is moving all the time, and processes like erosion and plate tectonics can change the appearance of an impact crater. In fact it is believed that we can only see 3% of all impact craters.  On places like the moon (where there is no atmosphere  erosion, or plate movement) we can very easily find impact craters. In fact if you look at the moon on a clear night you can see these craters with your naked eye.

So how can we find the evidence here on Earth?  Well there are other tell-tale signs of a meteorite other than the crater it forms.  The first major distinction is rocks that have undergone "shock-metamorphism".  As you may remember from science class metamorphism is a change in the physical state of an object.  In this case the metamorphosis is occurring to the rocks immediately surrounding the impact site.

Tektite

In other words, you can look at the rocks around the crater, and using certain tell-tale signs that they were dramatically altered in a short period of time.  A geologist would look for rocks that are melted, have crystal deformations or shatter cones.  Certain rocks that are commonly associated with meteorite impacts include spherulites and tektites.  Another common trait in these rocks is magnetism.

What does it me to you and me?
There is a very interesting history of meteors, and how they changed the world in the past.  The fate of human kind is still up for debate, and all in all everyone could be both right and wrong.  We do know (scientifically) that an asteroid (or meteor) killed the dinosaurs.  We also know that (based on that formula earlier) it is rare for large meteors to make it past our atmosphere.  And even if a meteor does make it, there is no guarantee of a cataclysmic event occurring.

All in all it comes down to this.  Scientist can predict the frequency and probability of meteor strikes.  We can calculate how long it will take to enter the atmosphere, how much of it will burn away, and approximate where it will land.  But knowing that will not prevent it from happening.  When it comes to meteorites we are all up to chance.