Friday, February 15, 2013

Science Vs. Meteorites

Dear Madame L,

After you wrote about the meteorite that was coming close to the Earth but not going to hit us, I was surprised to read this morning that it has hit Russia, killing thousands of people.

What's the story?

Sincerely,

You Don't Trust Bill Nye, But Who Should I Trust?


Dear Standing in the Corner Losing Your Trust in Science,

It was a different meteorite. You can read about it here.

But what Madame L is wondering is why "they" (you know, THEY!) didn't see this one. 

Madame L will let you know more as she finds out more.

Sincerely,

Madame L, Still Trusting Astronomers More Than Bill Nye

2 comments:

Laura said...

From what I read, this one was only two meters wide. Is it possible that one that small just doesn't make it on the radar (so to speak) of astronomers? Also, people were only injured, mostly from shattering glass as they got close to windows to see what was causing the noise, than from the meteorite itself.

I read another interesting blip about why so much of it was captured on dashboard cams - it's because Russians are apparently horrible drivers so many people have dashboard cams as liability protection.

But I'm rambling now, and this is your blog, Esteemed Madame Elle, not mine.

Jeff Wynn said...

More hypervelocity physics:

You can't find these things in time using radar for simple geometric reasons: The outgoing beam has energy falling off as the distance squared (you are painting the inside of an expanding sphere). Reflection is not 100% efficient, so only a fraction even starts back, and this reflected signal ALSO falls off as the distance squared.

Bottom line: if you can "see" the incoming bolide with radar, it's already over except for the screaming.

They find these things - if they are big enough - using sunlight (the Sun generates much more energy than any radar system). Atronomers calculate ever improving orbits from the telescopic data-points. Something like DA14 is a VERY faint object, and wasn't seen until it was already pretty close. Part of the reason is albedo: the albedo of the Moon is just 6%: only that much light from the sun even gets reflected. If something is covered with ice (e.g., a comet) you have a better chance of seeing it at a greater distance. If the Moon was covered with ice, you would not be able to look at it.

The kinetic energy these things bring with them goes as the mass times the velocity squared. Double the velocity and you quadruple the whack.

Incidentally, not to make you nervous, but comets can enter the inner Solar System at velocities as high as 75 kilometers per second.

NASA and the Air Force STILL haven't completed an inventory of Near Earth Objects greater than one kilometer in diameter.

Evidence on the ground (Wabar, Meteor Crater, etc.) suggests that far smaller NEO's would be "city busters"; something 1 kilometer in diameter would devastate a continent.

As a rule, the smaller an astral object, the more common it is: Tunguska sized bolides (50+ meters) are probably going to hit every century or two.

I published a paper in 1999 that lists 5 "city busters" that have hit on land just since 1863. I wonder how many tsunamis in that time (15 would be about right) had nothing to do with seafloor earthquakes?
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