Reply to post: Re: WHy bother looking at asteriods that will destory earth?

What would you prefer: Satellite-streamed cat GIFs – or a decent early warning of an asteroid apocalypse?

AdamT

Re: WHy bother looking at asteriods that will destory earth?

probably, yes. if they had sufficient good data on the asteroids path. Generally they are lumps of rock coming straight in at very high relative speeds. They take so little time to pass through the atmosphere (don't believe Hollywood!) that they don't get diverted by it much. The biggest uncertainly (for certain size ranges, at least) is whether it will make it to the ground in one lump or whether it might explode into fragments on the way in. For example, the Chelyabinsk event from entry to fragmentation was about 15s (after-effects obviously lasted longer).

Satellites are a bit harder as they are very small and it is atmospheric drag that brings them down. For that you need to track them and model the effect of a non-streamlined irregular object interacting with the outer wisps of the atmosphere (which grows and shrinks), etc. So what starts as a very gradual slow down and de-orbit can suddenly suddenly change into a much more rapid descent if it "digs in" or the outer atmosphere is a bit thicker than expected that week, etc. For the last large object that I can recall (which I think was the Chinese prototype space station) the impact estimates were updated regularly and became increasingly accurate as it orbited closer in and the atmospheric effects became more consistent.

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