The Surface is Too Rough for a Meteorite

For small meteoroids, 90% of the mass is lost to ablation as they comes through the Earth’s atmosphere. Edges, “corners,” rough surfaces, and any other protuberances are the first parts to ablate away. Put an ice cube in water and wait for 90% to melt. The “cube” that’s left will have no edges or points. It’s like that with meteorites.

As a consequence, most stony meteorites have rounded and smooth exteriors, except where they have broken.

Two views of meteorite Northwest Africa 7496 (polymict eucrite). This is a typical meteorite in being rounded and having having a dark, glassy fusion crust, except where it has broken. Photo credit: Randy Korotev


The rocks below are not meteorites because the surfaces are too rough (and, of course, none of them have fusion crusts).

 

The observant among you may note, “…but you have photos of lot’s of lunar meteorites with rough exteriors on your lunar meteorite website. Correct, but there are “extenuating circumstances.”

Hot-desert lunar meteorites with rough surfaces. The terrestrial age, if known, is given in yellow

First, less that 1 in 1000 meteorites is from the Moon and so far, none has been found in Europe, North America, or South America. All lunar meteorites with rough exteriors are from hot deserts, mainly northwest Africa (NWA) and Oman (Arabian peninsula). Most of these have been lying at the surface of the desert for tens to hundreds of thousands of years. During that time they have been “sand blasted” by wind-blown sand, which has removed their fusion crusts and preferentially dug deeper into some places of the surface of the meteorite than others. Others are pieces of larger meteorites that have simply fallen apart over thousands of years, e.g., Dhofar 1085 (Oman) in the upper left.

Few if any meteorites found in the U.S., for example, have been exposed at the surface, the place where most meteorites are found,  for “tens to hundreds of thousands of years” because there are no surfaces that old in North America. (If someone knows this statement to be incorrect, please let me know. I believe that terrestrial ages of even Roosevelt County, NM, meteorites are in the 10,000-50,00 year range.) We just are not going to see weathering like this in a meteorite from a temperate climate. For ordinary chondrites, ~95% of stony meteorites, the metal will rust and cause the meteorite to break apart into friable debris; they do not remain as solid rocks like those above.

So, I stick with my story: Unless you found the rock in a desert, if it has a rough surface with no fusion crust, then almost certainly it is not a meteorite.

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