Geologists Puzzle Over Egyptian Craters

A set of craters deep in the Egyptian desert has geologists scratching their heads.  Discovery Channel News says that they look neither like impact craters nor known volcanic phenomena.  “It is a strange and new thing,” reported one French scientist.  Jay Melosh of the University of Arizona remarked, “There’s nothing in our current geological literature that describes them.  It would be most valuable to try to figure it out.”
    The impact of these craters may reach beyond the Earth.  If some unknown process caused these structures, planetary scientists may have to reconsider the origin of at least some surface features on other worlds:

Besides explaining the Gilf Kebir region, the information might prove useful elsewhere on Earth and beyond.  Mars, for instance, was once rich in both water and volcanism, and today the planet has plenty of cratered-looking land, Melosh explained.  Perhaps some of those famous pockmarks are not impact craters either.

The article has land-based and satellite pictures of some of the craters.  There are some 1,300 of them.

Wouldn’t it be something if the explanation turns out to involve a non-impact process, like a new method for internal heat to escape from the interior, unlike classical volcanic or hydrothermal processes?  In Death Valley, for instance, the Ubehebe Crater and neighboring bowl-shaped features were thought to have been formed by steam explosions.  What if planets or moons had global episodes that, like acne outbreaks or bubbling oatmeal, produced vast numbers of circular features simultaneously?  If that sounds bizarre, it can’t be much more unexpected than finding geysers on Enceladus (11/28/2005) and Mars (08/17/2006).  For decades, scientists have merely assumed that most round, rimmed craters in the solar system were caused by impacts.  Undoubtedly, many were formed that way.  Features such as crater rays, ejecta blankets and central peaks may prove diagnostic of impacts, if other processes are incapable of mimicking these effects.
    Remember that scientists have never witnessed a large impact crater being formed (the impacts on Jupiter in 1994 don’t count, because that was not a solid surface).  Meteor expert Gene Shoemaker used to shoot bullets at rocks to study impact effects, but whether his experiments on small scales can be extrapolated to all scales is an assumption, not an observation.  Even if impacts are the primary cause, they might not be the only cause.  The possibility that some Martian and lunar craters may have formed internally, combined with the revelation that secondary cratering is common, (06/08/2006) could have major ramifications on our theories about planetary surfaces – and how old they are.  Here we see structures right on our home planet that don’t fit any of the standard geological explanations.  Puzzles are good for science.  This should be an interesting case to follow.