<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I must admit, my initial prediction of squarish polygons well before arrival, at the time may had seemed boneheaded (on the old closed thread), but on Sol 0, one of the very first post EDL images showed just that, a beautiful square polygon. ...</p><p>.Andrew Brown. <br />Posted by 3488</DIV></p><p> </p><p>crap - I just wrote you a long, detailed post about this, then it deleted because I used the spell checker.</p><p>Let me summarize:</p><p>I really doubt that the phases ice 1c (squarish) and ice 1h (hexagonal) are related to the shapes of the polygons on the Martian surface.</p><p>When ice freezes it forms a collection of microcrystallites of random orientation fused on the crystal edges. It does not typically form a single perfect ice crystal a meter on edge. To form a crystal this big, you would need very perfect circumstances (water purity, lack of nucleation sites, controlled very slow growth, etc).</p><p>Polygon shapes in terran permafrost are not due to the ice wanting to freeze in a hexagonal form. Rather they form as a result of annual freeze-thaw cycles which create a slow thermal convection process at the polygon boundries. In a sense this is very much a modified Benard cell circulation. Please look up my thread on this subject in the old pre-Pluck SDC forums about 3 yrs ago for more information about Benard cell mechanisms.</p><p>I don't know even if the shape of the polygons on Mars is squarish. I would like to see a top-down photo map projected in Cartesian coordinates, with the photo contrast enhanced to make the polygon boundries easily visible. This could be constructed using software from the current photo images. Unfortunately, I still haven't seen this. Rather I have seen photos directly from the lander, or photos in a polar coordinate system centered on the lander. This perspective distorts shapes badly. If you have seen a top-down photo map constructed from the lander photos replotted using software ona square Cartesian grid, please let me know.</p><p>If indeed the Martian polygons are squarish, I don't know the mechanism. But the cause of putative squares is almost certainly not that ice 1c phase prefers to form square crystals.</p><p>You know, if we had a microscope with a polarized filter, then examination of original unscraped bulk ice surface would be easily able to see the ice microcrystallite boundries. This would be interesting! And if the microscope had a dark-field attachment, then by examination of original unscraped bulk ice we would be able to easily see the deeper phase boundries, and also embedded particles, air bubbles, and (if these existed) any putative embedded oil drops or putative organic matter. I don't know if we have such an attachment on the lander microscope, nor any capability to move the microscope next to a virgin unscraped ice surface.</p> <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>