Friday 15 February 2013

Difficulty estimating size

In addition to the question of the meteor trajectory, we have been trying to estimate the size of the object. This is extremely difficult as there are a large number of parameters that can affect the result of any impact.

Of course, for the Chelyabinsk event, we are trying to work backwards, based on reports, video footage, and any other data we can obtain. In the excitement of the moment, we need to bear in mind that some reports can be exaggerated in the excitement, so it is necessary to be cautious.

The result of the impact can be affected by the size and density of the object. How it is formed (and how it fractures) can be significant. Video footage from some angles suggests that the object split into two roughly equal parts (based on smoke patterns). There have been suggestions of fragments (and even a crater!), but we don't have any details. When confirmed, this will be critical in not just size estimates, but also in improving our estimate of the trajectory.

The velocity of the object is also of importance. Faster moving objects will do more damage. Therefore, for an equivalent explosion, a slow-moving fragment would be comparatively bigger than one that was fast moving. The movement of the Earth through the Solar System means that "near dawn" events may be compounded by the "head-on-collision" effect. Again, as our knowledge of the trajectory improves, so too will our impact parameter set.

As more data comes to hand, we will continue to revise our information and will post something when we can.

However, the Chelyabinsk event is certainly much smaller than the 2012 DA14 asteroid.

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