# Thread: Lunar history and how size of crater depends upon size of meteors

1. Newbie
Join Date
Sep 2007
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4

## Lunar history and how size of crater depends upon size of meteors

Hi all, this is the first time I'm posting here. I developed an interest in astronomy ever since I took up an astronomy module in my college. I'm always curious about lunar history and how size of crater depends upon size of meteors. Can any kind souls give me some explanations or provide me with any book titles or websites that give good description with regards to my query.

2. The short answer I've heard is that any meteorite large enough to explode on impact (which might be pretty small for the Moon as it has no atmosphere to slow the incident rock) makes a circular blast crater with radius about 10 times the radius of the rock.

3. Order of Kilopi
Join Date
Jul 2005
Posts
9,761
On Earth, there's an approximate power-law relationship between the energy of the impactor and the diameter of the crater:

D = 0.02 x E1/3.4

where D is the diameter in metres and E is the energy in joules.

To allow for differences in excavation efficiency and post-excavation slumping on other planets, you need to multiply by a jigger factor equal to g-0.2, where g is the surface gravity expressed in Earth gravities. So for the same energy of impact on the moon, you get a crater ~1.4 times bigger than you would on Earth.

(The equation is derived from Martyn Fogg's Terraforming textbook.)

Grant Hutchison

4. Newbie
Join Date
Sep 2007
Posts
4
Thanks guys!

Another question, I took a photo of the moon, and I'm doing a project right now, trying to determine the crater density and all that. How do I go about doing it, as in what kind of graphs to plot or what equations to use?