Shape of craters

[bdewoody]

Is the shape of a crater from an object determined by the angle it hits the surface, ie if the impact is nearly vertical the crater is round and if the angle is very oblique the crater is elliptical?<br /><br />If this is so it looks like most hits are nearly vertical. <div class="Discussion_UserSignature"> <em><font size="2">Bob DeWoody</font></em> </div>

 

[vogon13]

It may be possible the squarish shape of the Barringer Crater may be due to fragmentation of the impactor just prior to contact with earth's surface.<br /><br />Note: The crater is still pretty close to circular.<br /><br />There are some elongated craters on Mars too. Perhaps decayed 'stable mates' of Phobos and Deimos.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[MeteorWayne]

That's not really an exception, CE. They're not particularly round, IMO<br />(assuming I'm looking at the right ones)<br />MW <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[JonClarke]

My understanding is that the square shape of Barringer Crater (AKA Meteor crater, Arizona) is due to preferential slumping along pre-existing orthogonal joints. The underlying strutural control on the wall orientation was for many years used as evidence for an endogenous (terrestrial) origin for the crater by those opposed to an impact explanation.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[yevaud]

Here's a back issue of the <i>Physical Review Focus</i> from 2003, which explains some experiments in how craters are created.<br /><br />There are two kinds of craters: a "Simple" crater, which has a round, somewhat uniform bowl shape, and a "Complex" crater, in which a central, raised mound from slumping due to gravity, due to the size of the crater created: small craters usually form Simple shapes, largish craters tend towards the Complex shapes.<br /><br />This is a good, topical overview I'd run into back when:<br /><br />Terrestrial Impact Craters <br /><br />(Oh, sorry. Edit: this post meant as information for all participants, not Jon, who knows this stuff quite well) <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[3488]

Rhea, Saturn's second largest moon has many polygonal craters & the Uranus moon Umbriel also sports a few.<br /><br />Something to do with the surface compostion or just due to there being so many craters that no more could fit in, without covering pre-existing craters??<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[JonClarke]

I would suggest crustal polygonal fracture systems controlling how the crater walls collapse during formation.<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>

 

[JonClarke]

Two nice articles on polygonal craters are <br /><br />http://www.geo.su.se/file.php?id=4936<br /><br />and<br /><br />http://www.apl.ucl.ac.uk/lectures/3c11/impacts2.pdf<br /><br />Jon <div class="Discussion_UserSignature"> <p><em>Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars</em>  Arthur Clarke</p> </div>