Phil, perhaps you might want to do something about that…

It has taken some time, but my concept of obvious doesn’t make it to the average adult american… obviously.

PB

It was black in color but the underlying color was that of nickel. There was a small cavern in the rock with something that looked like some kind of hard dark crystal embedded in it.

As far as I know it was a naturally accuring metal/mineral. Any ideas?
Wish I knew where I put it. I think its somewhere in an old box in storage.

At least, that’s my understanding of the process.

DK

http://seds.lpl.arizona.edu/nineplanets/nineplanets/meteorites.html

It says: However meteoroids larger than a few hundred tons are slowed very little; only these large (and fortunately rare) ones make craters.

The page seems to catch the general sense of what I was after. Sooo, if we assume that “a few hundred tons” translates to 200-500 tons, and we will conjecture that they mean metric tonnes, not imperial or US tons, we can make the following calculations:

1. density of iron: 7874 kg/m3
2. density of chondrite stone: 2670 kg/m3

Smallest one would be 200ish tonnes of iron, or about 25 cubic metres. The larger end of the threshhold would be 500 tonnes of chondrite, or about 190 cubic metres. Assuming perfectly spherical asteroids (God’s billiard table ), that translates to about a 4m diameter ball of iron, to about a 7m ball of chondrite stone.

Thus, I guess the sort of “nasty crater” threshold is about 5-10m, over which they generally make traditional craters, and below which they are just kind of annoying to have land on you.

Ah, the wonder of the internet!

It may interest some of you that Concorde (remember that?), when travelling at Mach2 at 60,000 feet, used to grow, in length, one foot due to thermal expansion. Under the carpet in the aisle, the floor is made of separate plates, and apparently (if you take the carpet up) you could see them move (and if you can see daylight, you should tell somebody … ). Of course, it shrank again as it slowed down.

Across the cockpit windows at the front of the aircraft, there was a heatshield that protected the pilots from the compressive / frictional heating. It also meant they couldn’t see where they were going. They still had the little side windows (so they could see where they’d been), but there still is very little traffic at 60,000 feet so it was not really a problem.

Bro: (Singing while shooting with camera:) “Chickey cho chickee chee…�
Other guy: “Hey Bro do you see that?”
Bro: “What?”
(Giant asteroid the size of Manhattan screams in – enormous explosion – screen goes white hot – gigantic crater explodes – millions of tons of dust and molten rock soar into the upper atmosphere,) … and all through this we hear the guys in the truck going :”Yee Ha! Did –You- See -That?!” “Yeeee Haaaa!”

Welcome to the 42nd Tangled Bank, a semi-weekly compendium of the best science blogging.

there is no binary line where the object won’t reach terminal velocity before impact and therefore cause a large crater. it’s much more gradual. an object that would have reached t.v. 1 second after impact, and one that reaches t.v. one second before impact, are both going to have almost identical impacts.

http://faculty.rmwc.edu/tmichalik/moon8.htm

an interesting study would be how small craters are on the moon, where there is no atmosphere and thus no terminal velocity.