This program estimates the size of a projectile that made a gravity-dominated crater of the given size. Three different estimates are presented, but the Pi-scaling method is currently considered the best.

**Transient Crater:**
The cavity formed immediately after the end of crater excavation, before it undergoes collapse and modification. Its outer extent is defined by the boundary between excavated and non-excavated (but possibly displaced) target material, and its depth is the maximum achieved by material that will eventually form the floor of the true crater after cratering motions cease. Although it is by nature temporary, laboratory-derived scaling relations apply only to the diameter of the transient crater, not the final collapsed crater form. Collapse of a transient crater produces both simple and complex impact craters.

**Final Crater:**
The distance from rim to rim of the cavity once collapse has completed.

The Carolina Bays are shallow elliptical basins in the Atlantic Coastal Plain. The program to calculate projectile size from crater diameter assumes that the crater is circular. By equating the area of a circle to the area of an ellipse, we obtain the equivalent radius of the ellipse as the square root of the product of the semimajor(a) and semiminor(b) axes. The diameter of the ellipse (2r) can then be used to calculate the projectile size.

\(A = \pi r^2 = \pi ab \)

$$r = \sqrt{ab}$$

$$r = \sqrt{ab}$$

The width-to-length ratio of a Carolina Bay corresponds to the sine of the impact angle.
\(sin(\theta) = W / L\)

Thus, the impact angle can be calculated as \(\theta = arcsin(b/a)\).

The program is based on a FORTRAN 77 program originally written by **Prof. H. Jay Melosh**
and converted to Perl by **Ross A. Beyer**.
More information about the equations can be found in the book by Melosh:
Impact Cratering: A Geologic Process, Oxford University Press, 1989, or
in the related publication, below.

This program was originally hosted at the Lunar & Planetary Laboratory of the University of Arizona.
The files were removed when Prof. Melosh transferred to Purdue University.
The HTML file was archived on 3:28:10 Jan 11, 2016 and retrieved from the Internet archive on 22:27:34 Feb 4, 2016.
The program is free software under the terms of the GNU General Public License.

UPDATE Jun 1, 2019:

As of this date, the program was back in operation at URL:

https://pirlwww.lpl.arizona.edu/~rbeyer/crater_p.html

**Related Publication:**

Gareth S. Collins, H. Jay Melosh and Robert A. Marcus,
Earth Impact Effects Program: A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth, *Meteoritics & Planetary Science* **40**, Nr 6, 817–840 (2005).
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© Copyright - Antonio Zamora