Week 2: Craters on Mars and the age of the surface.

Web based GIS database on craters that you can explore.

Controls on crater morphology:

Fracturing, fractals and impactors.

What produces impactors?

What is a fractal geometry, a fractal distribution?

A theoretical distribution of broken blocks.

Actual distributions of fragmented materials (see handout).

Conclusions: a) impactors may follow a fractal distribution, and b) there is likely more than one population of impactors, each population with its own fractal distribition.

Good background reading: Turcotte, Chapt. 3, Fragmentation, in Fractals and chaos in geology and geophysics, Cambridge Press.

Crater distributions on Mars:

portion of LunaePalusMG15N293E.JPG - note the difference in crater density from left to right.

Excellent intro web document by Hartman.

ISOCHRONS FOR MARTIAN CRATER POPULATIONS OF VARIOUS AGES by William Hartman - Detailed description of Mars crater distributions and the construction of a temporal framework. http://www.psi.edu/projects/mgs/chron04a.html

The epochs of Mars.

 'geological' epochs  Ncum (>2 km diameter)  Ncum (>5 km diameter)  Ncum (>16 km diameter)
 Amazonian  <400  <70   --
 Hesperian  400-1200  70-200  --
 Noachian  >1200  >200  >25

Numbers from http://web.pdx.edu/~ruzickaa/G456/labs/Mars2.htm.

Summary from Hartman, http://www.psi.edu/projects/mgs/chron04a.html

Diagram showing size versus crater density isochrons for Mars, Hartman (2004).

Web based GIS database on craters that you can explore.

Arthur, D. W. G. 1954. "The Distribution of Lunar Craters." Journal of the British Astronomical Association, 64 (February), pp. 127-132.