Primaries or Secondaries?

[FLO]

Moltke crater is probably best known as a guidepost to the Apollo 11 landing site. It is a fresh, 7 km wide simple crater with steep bowl-shaped walls. This Apollo 10 image beautifully shows the ejecta deposits that surround it. On a higher Sun view the ejecta shows up as a bright patch; in this closeup it is seen as a thinning pile of bumpy hills (called hummocks by geologists) and beyond them tiny secondary impact craters....

Source: LPOD

http://www.lpod.org/?cat=32

[Andrew]

Awesome photo Steve and the web site is fully of equally spectacular images.

Thanks

[FLO]

Just a thought:

If the crater is 7km wide, how large do you think the object was that created it and why isn't it sitting in the center of the crater... Did it disintegrate?

[Astroman]

The object would probably be about 10 meters across, depending on composition. Most of it would be vaporized on impact, but I'm sure much of it is somewhere in the vicinity. Looking at the photo, you can see the right side ejecta blanket is larger than the left side. This means the object hit at a considerable angle, approaching from the left. If you'd care to mount an expedition, I'd go along and help. I'd start digging along the right side of the crater wall and check around the right side ejecta blanket.

[FLO]

If you'd care to mount an expedition, I'd go along and help.

I'll check my diary

Thanks for the explanation

[Andrew]

I read in 'Universe' published by Dorling Kindersley (which, incidentally, is excellent) that the craters on the moon are 15 times the size of the impacting body. So approx 450 m in diameter!

Apparently they hit at around 45000 mph, which presumably explains why there's not much left of the asteroid!

[FLO]

Apparently they hit at around 45000 mph, which presumably explains why there's not much left of the asteroid!

:shock: 8)

I'll check that book out at Amazon

[Andrew]

mmm, that's interesting Astroman - maybe 'Universe' isn't quite as excellent as I thought!

Don't suppose you can point me towards a basic outline of the mechanics that relate crater size to asteroid dimensions?

[Astroman]

I got my calculation from extrapolating the size of the impactor that hit the desert in Arizona. They figure it was around 5 meters and it left a crater about 2 km across. Yours is probably more accurate.

[FLO]

I heard somewhere (can't remember where) that there is a program on the net that calculates crater size and area of devastation following a meteor impact. Does anyone know where?

[Andrew]

Who knows - I'm just repeating what I read!

I guess there are differences in gravitational acceleration and atmospheric drag which must feed into the process somewhere. Also (and I'm guessing here) crator size must depend upon whether the surface is initially rock or loose material. Still, I'd like to see a summary of the basic equations involved.

[Astroman]

Here's a link:

http://www.lpl.arizona.edu/impacteffects/

University of Arizona

[FLO]

Fantastic 8)

The fun begins....

Thanks AM

[Astroman]

Who knows - I'm just repeating what I read!

I guess there are differences in gravitational acceleration and atmospheric drag which must feed into the process somewhere. Also (and I'm guessing here) crator size must depend upon whether the surface is initially rock or loose material. Still, I'd like to see a summary of the basic equations involved.

You're right, Andrew. Thing is, at higher velocities the atmosphere won't slow the impactor down much if it's at a steep entry angle. But the energy released, regardless, is something to think about.

[Andrew]

Amazingly, my quick search turned up almost the same web site (at least by the same authors). Slight difference with this calculator is that it allows you to vary gravity to work out crater dimensions for the moon and other planets. I think I'm going to have a play with this

http://www.lpl.arizona.edu/tekton/crater.html

[Andrew]

Interestingly, assuming a vertical impact and dense rock for both asteroid and moon this calculator throws out a diameter of 467 m (exactly 15 times the crater diameter).

DK, I take it all back!

[Astroman]

Well, there ya go. Trust an author, not "off-the-top-of-the-head" calculators.

[Andrew]

Actually the figure I got was for an impact in loose material.

Also, according to that web site the relationship between crater size and impact body is nonlinear - so DK have over-simplified things and the magic number of 15 just arose for this particular crater.