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Originally Posted by Toughy
Where is Aj? She explains stuff really well (that was horrible english...lol). If I remember there are a whole mess of little meteors or asteroids or chunks of rocks that accompany the big daddy meteor.. and is what exploded over Russia......that is how they work I believe.
NASA swears the big daddy will not hit earth.
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So Asteroid 2012 DA14 made its closest pass to Earth about 11:43 Pacific today. The meteor that exploded over Russia had nothing to do with the asteroid it just so happens that the two objects were in close proximity to Earth at the same time. That actually isn't all that rare.
Generally, Toughy, anything that makes it this far into the system is going to be pretty much a whole chunk, at least until it hits atmosphere. What happened with the meteor in Russia is that it did not actually hit the ground in one big chunk. As these things are measured it was pretty small (about the size of a bus and weighing about 7000 pounds) It exploded about 30 miles up and released the energy equivalent to about 20 Hiroshima sized bombs (~320 kilotons of TNT) but most of that was absorbed by the atmosphere. What actually hit the ground were smaller fragments that were left when the meteor exploded.
I think what you're thinking of is what happened when Comet Shoemaker-Levy slammed into Jupiter. That was different for a couple of reasons. The first and most important here is that Jupiter is HUGE. It would take 11 Earths lined up side-by-side to stretch across Jupiter's diameter. It would take 1321 Earths to equal the volume of Jupiter. It would take 122 Earths, flattened out, to cover the surface of Jupiter. It would take 318 Earths to equal the mass of Jupiter. It's gravity at the surface (if it had a surface which it doesn't) would be 2.5 times that of Earth. I say that because in order to understand what happened to Shoemaker-Levy you need to have a sense of scale. Jupiter quite literally tore the comet apart as it approached the big planet. It's called tidal forces. For reasons I won't get into now and even though you don't realize it, there is slightly *more* gravity pulling on your feet than on your head. You don't realize it because the difference is very slight because Earth doesn't have the mass to have strong tidal forces (this is different than the tides). Jupiter, on the other hand, has sufficient mass for tidal forces to be noticeable to something like a comet that has been captured in its orbit. So the head of the comet felt more of Jupiter's gravity than the end of the comet and it ripped the comet apart. The pieces then fell into Jupiter over the course of a few days.
The meteor that exploded over Russia did so not because of our gravity but because of our atmosphere. It hit the atmosphere doing about Mach 50 (50 times the speed of sound or 33000 miles per hour. To give you a sense of scale, the Space Shuttle would reenter at ~17500 or Mach 25. The fastest true airplane built so far is the SR-71 Blackbird which would get up to ~Mach 4). When it hit the atmosphere that fast it heated up very quickly. When things heat up, they expand. You get the idea. Typically this is the fate of most objects that enter our atmosphere.
The *really* big stuff are the rocks that actually make it through our atmosphere and hit the ground. To give you a sense of scale, the rock that exploded today was about 49 feet wide. The asteroid that passed close by was about 150 feet across. The rock that delivered the coup de grace to the dinosaurs 65 million years ago was about 6 miles across! There was enough of it when it hit the ground that it took a chunk out of what is now Eastern Mexico and vaporized it!
If anyone has other questions about either the asteroid or the meteor explosion I'll do my best to answer them.
Cheers
Aj