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General Science => Question of the Week => Topic started by: thedoc on 16/04/2012 12:25:47

Title: QotW - 12.03.11 - How would I know if a meterorite was falling towards me?
Post by: thedoc on 16/04/2012 12:25:47
If there were a large object, say a meteorite falling straight down where I'm standing, what kind of warning would I notice? Would there be an accompanying sound that could warn people on the ground? Or would I not know until it's too late?

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Daniel Spain
Nashville, Tennessee USA
Asked by Daniel Spain

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Title: QotW - 12.03.11 - How would I know if a meterorite was falling towards me?
Post by: thedoc on 16/04/2012 12:25:47
We answered this question on the show...

We put this question to Dr Mark Lewney, who gained his PhD in Acoustics from Cardiff University...
Mark -   For most of us here on the Earthís surface, the speed of sound is around 340 m/s or 750 miles an hour.  That's one mile every 5 seconds which is actually not all that fast.  Itís only about twice the speed of the fastest arrows in archery.  Sound is also even slower in colder air and the air altitude is both colder and much less abundant.
So when the meteoroid, the lump of rock itself enters the atmosphere 100 km up and becomes a meteor, it will always be too far away to hear.  Itís possible that its electromagnetic waves travelling a million times faster than its sound waves will cause a hissing noise in phones or radios, but even this so-called electrophonic effect is debatable.
[img float=right]/forum/copies/RTEmagicC_planet-bombardment_02.jpg.jpg[/img]But Daniel asks not about a meteor which burns up in the atmosphere but a meteorite which actually makes it all the way through the atmosphere to the Earthís surface.  Would this give any warning?  Sadly, no.  It will be travelling at least 11,000 metres a second, 33 times the speed of sound, far too fast to hear its approach.  In fact, we probably wouldnít be able to see it either.  Only a tiny fraction of the solar systemís asteroids are currently being tracked by just a handful of volunteers worldwide.  So unless it reflected the light in just the right way in a small region of the sky that someone happened to be looking at very carefully, it would almost certainly be too small and too fast to see until it entered the atmosphere just a few seconds before impact.  I'm afraid Danielís final moment would be rather disappointing.
Hannah -   Poor, Daniel.  Mark adds that it is possible that the meteorite will burn up just enough to be decelerated by the atmosphere to subsonic speeds.  But that this would leave a meteorite so tiny that getting killed by it would be a bit embarrassing.
Title: Re: QotW - 12.03.11 - How would I know if a meterorite was falling towards me?
Post by: CliffordK on 04/03/2012 21:12:48
Assuming the meteorite was travelling at supersonic speeds, there would be no sound until after the impact.  So, you would have to rely on either tracking the meteorite before it impacts Earth with our NEO warning system, or watching the flash of light as the meteorite enters our atmosphere.

It is easier to view "falling stars" at night than during the day.
Title: Re: QotW - 12.03.11 - How would I know if a meterorite was falling towards me?
Post by: Cheese2001 on 05/03/2012 02:05:04
You can always tell if you're on a collision course with anything by a simple rule known as "constant bearing, decreasing range."

Title: Re: QotW - 12.03.11 - How would I know if a meterorite was falling towards me?
Post by: beveridge on 06/03/2012 10:12:51
I think you might feel a shock wave a few milliseconds before you are squashed and you might notice a bright light from re-entry.

This made me think of a past event had personal experience with....
 I was skiing in Banff Canada on a snowy spring day when we came across a man taking pictures of his girlfriend. The hair which hadnít been dampened by the snow yet was standing on end as if charged by a Tesla coil. I thought this very odd and sat back to wait for my friend to get closer.
When wearing skis it is sometime comfortable to lie back on the snow and have your skies planted in the ground in front of you vertically. As I am laying back I notice a very high pitched whistling noise but canít tell where it is coming from because of the pitch.  I suspected my ski but thought this impossible. I did confirm it was my ski because as I changed the angle of it from vertical the intensity changed as well.
This was the strangest scene I have experienced in my life and caused a strange primal fear in me.  I fear very little in life but kind of creeped me out.
As I used to be a private pilot I felt comfortable phoning a weather expert at the Calgary airport to see if they had any idea what these events were all about. It was explained to me that we were in a channel of high charge where a lightning strike was likely to occur. The charge builds until it becomes high enough for the air to conduct a lightning bolt.  I was told if this occurs again to get down immediately.
For those who live where there is snow you might think that lightening does not ever happen in the winter when snowing. But remember this was the spring and in the mountains thousands of feet up. It might be snowing up there and raining down lower by way of cumulus clouds.
Love the show..

Title: Re: QotW - 12.03.11 - How would I know if a meterorite was falling towards me?
Post by: CZARCAR on 07/03/2012 18:46:12
air compression?
Title: None
Post by: steve on 05/11/2012 05:39:26
Ah.  But the air between you and the asteroid hitting the top of the atmosphere will be compressed to a fraction of its size in about 1/100 of a second.  This will raise the temperature on top of his head to about 8000K.  So, theoretically you will know the meteor will hit you before it does as all your hair will be burnt off just before impact.  Of course, you'll be to busy being incinerated and turned into a plasma to bother noticing.