Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Moon Crater Shapes
Name: Tom
Status: other
Age: 40s
Location: N/A
Country: N/A
Date: 1999 - 2000


Question:
The craters on the moon are obviously round but impacts with a grazing incidence should leave a V shaped crater. I would think that some percentage of the impacts would be at shallow angles of attack but this does not appear to be the case in photos.

Have they discovered such craters and if not why??


Replies:
It doesn't work that way. A crater is like a frozen ripple, and ripples are round. There is an asymmetric distribution of matter in the ripple, and the blanket of stuff ejected from the surface, that do record the angle of incidence. These are superimposed on the ripple, but it's the ripple that is most noticeable because of its sharp edges.

Tim Mooney


Actually, impacts at a grazing angle will also make a round hole. This was a controversial point regarding Meteor Crater in Arizona, which was basically the first site recognized on Earth as a meteor impact site. The fact that no meteorite fragments were found in the earth below the center of the crater was initially taken as evidence against the hypothesis that the structure was an impact crater, but further research showed that if the impact is very energetic, such as a rifle bullet fired into mud, the resulting hole is round, even if the impact angle is quite flat.

Richard Barrans Jr., Ph.D.



Click here to return to the Astronomy Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory