The authors of this article also did a lot of crater size distribution counting, and found and studied several very fresh craters on the Martian surface (some only 40 days to 5 months old), to determine the rates of erosion and loss of dark colored rays in the surface next to the craters. This analysis helped them to date the age of the recent water flows.<br /><br />But, also interesting to me is this quote from the Nature article, in their discussion of their observations of cratering, as it bears on our speculations on the cause of the Martian 'microcraters':<br /><i>For example, the compact<br />distribution of craters in the multiple-crater<br />sites suggests that the breakup occurred relatively<br />close to the surface and with relatively<br />low dispersive energy. The similarity<br />in size of these craters and the general absence<br />of substantive surface disruption between<br />the craters suggests that the meteoroids<br />disaggregated into a small number of similarly<br />sized pieces. Our results appear to confirm<br />models that the smallest craters formed by<br />hypervelocity impact are likely to be a meter<br />or more across (6) and suggest that micrometeoritic<br />impact gardening or breakup of surface<br />materials is a relatively minor component<br />of martian erosion.</i> <br /><br />If you follow their argument, I believe this suggests perhaps that the microcraters we have observed might have been caused by the impact of smaller slower-moving pieces generated by the mid-air breakup of meteorites not that far from the surface. Interesting. <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>