Strange Craters Formed by Oblique Impacts
Large Oblique Impact Crater on Venus
It's located at about 6 degrees S, 6 degrees W long. The USGS Venus crater
database now refers to it as "Graham" with a "diameter" of 75 km (120 km x
45 km), although it is classified as "irregular".
- The crater itself is in the upper
center portion of the radar image; the radar dark region to the south
is that peculiar depression into which no ejecta appears to have
landed (or the radar dark stuff came after the ejecta was emplaced).
- Graham's impactor may have came in from the north (north is up
in the image you have).
Large Oblique Impact Crater on the Moon
- This is the Schiller crater on the Moon (180 x 65 km). It is
very similar to the "Graham" crater shown above.
Large Oblique Impact Crater on Mars
- This is the Orcus Patera on Mars, a huge (380 x 140 km) elliptical
impact at 14 deg N Lat., 180 deg. Long. Again, note the simularities between
it and the structures shown above.
How do you make such craters?
- These craters were probably formed by oblique, low-angle impacts
by asteroids or comets tens of kilometers in diameter.
- However, there are several examples on Venus of disrupted
materials hitting the surface and making a real mess of things.
- Graham may have been disrupting on the way down; that's
probably why the little crater to the north is connected to main one.
The rims of Graham are somewhat scalloped (not quite as much
as Schiller) and there are nasty scars downrange where smaller
materials hit (possibly spalled off/decapitated from the main
body of impactor(s)).
- Pete Schultz has a discussion on Graham
in one of the Magellan 6-month report articles that appeared
in JGR in 1992.