Re: [meteorite-list] Meteor Crater Shape and Entry Angle
How about SW to NE? I believe there are several finds along that path that match the Canyon Diablo material. -Original Message- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of Meteorites USA Sent: Friday, September 10, 2010 10:38 AM To: meteorite-list@meteoritecentral.com Subject: Re: [meteorite-list] Meteor Crater Shape and Entry Angle Hi John, Thanks for the details. It's interesting to note that the angle of descent is not known, though there are educated guesses or calculations. What can probably be agreed is that an impactor with an entry angle of 45* degrees could produce a round crater. Meaning of course that Meteor Crater, since it's not perfectly round as evidenced by the "bulges" in the NW and SE corners, must have been produced by an impactor with a trajectory much shallower than 45 degrees. Logically. Here's another question. Which direction was it traveling SE to NW or NW to SE? According to the Shoemaker paper here: http://arrowsmith410-598.asu.edu/Lectures/Lecture16/i0-8137-5402-X-2-0-399Sh oemaker.pdf "...Somewhat greater energy was required if the projectile struck at an oblique angle, as suggested by the presence of faults with underthrust displacement on the north and west walls of Meteor Crater" It suggests a NW direction of travel... is this correct? And how do we know? Does the "underthrust displacement" imply that the impactor was traveling from the SE toward the NW? Eric On 9/10/2010 8:05 AM, Kashuba wrote: > Eric, Bernd, Sterling, List, > > David Kring of LPL put together a great guidebook for the 2007 MetSoc tour > of the crater (150 pages). He is Gene Shoemakers successor as advisor to > the Barringer family. He and family members lead the tour. Carolyn > Shoemaker was there too. > > Chapter 9. "Trajectory" begins and ends thusly: > > The trajectory of the impacting asteroid is another issue of considerable > debate and still unresolved. > Historically, circular plan views of impact craters confounded many > investigators who assumed a circular > crater requires a vertical impact. They wondered why more craters are not > elliptical. Gilbert and > Barringer both realized that 45 degree impacts are the most probable > trajectories for meteoritic material. > Yet Gilbert, like many of his contemporaries, mistakenly thought a 45 degree > impact produces an oval > crater (Hoyt, 1987). Barringer, on the other hand, realized that a 45 degree > impact will produce a round > crater (Hoyt, 1987). Despite this insight, Barringer, like Gilbert, > initially assumed that the northern > Arizona impact had been vertical or nearly vertical and that the asteroid > was buried beneath the center of > the crater floor. > > When extensive drilling did not locate a main mass beneath the crater floor > and instead only > produced traces of the projectile, Barringer began to consider other > options. He had already noted several > features that seem to have a directional symmetry. > > - snip - > > More recently, techniques similar to those of Sutton were applied by > Holliday et al. (2005) to the > Odessa impact site. They estimated the Odessa craters were produced > approximately 63,000 years ago. > Although the ages of Barringer and Odessa craters are still not precisely > known, these approximate ages > suggest Odessa formed earlier, with the caveat that the Barringer crater may > be older than 49,000 yrs. > (See discussion in Chapter 11). Thus, the two impact events may not be > directly related and may not have > any bearing on the issue of trajectory. > > Nonetheless, several other potential indicators of trajectory survive (and > even the Odessa connection > might be revived). Unfortunately, these indicators cannot be reconciled at > the present time and I think it > fair to conclude that the trajectory of the impacting asteroid that produced > Barringer Crater remains > uncertain. > > Chapter 9: > http://www.lpi.usra.edu/publications/books/barringer_crater_guidebook/chapte > r_9.pdf > > Whole "guidebook": > http://www.lpi.usra.edu/publications/books/barringer_crater_guidebook/index. > shtml > > > Regards, > > - John > > Ontario, California > > > -----Original Message----- > From: meteorite-list-boun...@meteoritecentral.com > [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of > bernd.pa...@paulinet.de > Sent: Friday, September 10, 2010 3:26 AM > To: Meteorite-list@meteoritecentral.com > Subject: [meteorite-list] Meteor Crater Shape and Entry Angle > > Eric wrote: > > "The crater is not perfectly round as would be expected from an impactor > coming in at a sharper an
Re: [meteorite-list] Meteor Crater Shape and Entry Angle
Not at all logically. Meteor Crater was round after the impact. Its current shape is produced by the non-isotropic nature of the local geology. In essence, it has eroded into its current shape. This process is well understood. There is no evidence at all that the impactor arrived at a shallow enough angle to actually produce an oval crater. With our current crater analysis skills, I'd say any suggestion of a specific impact angle or direction is scarcely better than a pure guess. And even the reports estimating mass and velocity I view with a high degree of skepticism. Chris * Chris L Peterson Cloudbait Observatory http://www.cloudbait.com - Original Message - From: "Meteorites USA" To: Sent: Friday, September 10, 2010 11:37 AM Subject: Re: [meteorite-list] Meteor Crater Shape and Entry Angle Hi John, Thanks for the details. It's interesting to note that the angle of descent is not known, though there are educated guesses or calculations. What can probably be agreed is that an impactor with an entry angle of 45* degrees could produce a round crater. Meaning of course that Meteor Crater, since it's not perfectly round as evidenced by the "bulges" in the NW and SE corners, must have been produced by an impactor with a trajectory much shallower than 45 degrees. Logically. Here's another question. Which direction was it traveling SE to NW or NW to SE? According to the Shoemaker paper here: http://arrowsmith410-598.asu.edu/Lectures/Lecture16/i0-8137-5402-X-2-0-399Shoemaker.pdf "...Somewhat greater energy was required if the projectile struck at an oblique angle, as suggested by the presence of faults with underthrust displacement on the north and west walls of Meteor Crater" It suggests a NW direction of travel... is this correct? And how do we know? Does the "underthrust displacement" imply that the impactor was traveling from the SE toward the NW? Eric __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Meteor Crater Shape and Entry Angle
>>What can probably be agreed is that an impactor with an entry angle of 45* degrees could produce a round crater. Meaning of course that Meteor Crater, since it's not perfectly round as evidenced by the "bulges" in the NW and SE corners, must have been produced by an impactor with a trajectory much shallower than 45 degrees. Logically.<< I don't know, but I wonder if the shape of the terrain upon impact(hills/gulleys etc) or perhaps a varied pattern of rock strength underground could have had some influence to the craters shape? GeoZay __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Meteor Crater Shape and Entry Angle
Hi John, Thanks for the details. It's interesting to note that the angle of descent is not known, though there are educated guesses or calculations. What can probably be agreed is that an impactor with an entry angle of 45* degrees could produce a round crater. Meaning of course that Meteor Crater, since it's not perfectly round as evidenced by the "bulges" in the NW and SE corners, must have been produced by an impactor with a trajectory much shallower than 45 degrees. Logically. Here's another question. Which direction was it traveling SE to NW or NW to SE? According to the Shoemaker paper here: http://arrowsmith410-598.asu.edu/Lectures/Lecture16/i0-8137-5402-X-2-0-399Shoemaker.pdf "...Somewhat greater energy was required if the projectile struck at an oblique angle, as suggested by the presence of faults with underthrust displacement on the north and west walls of Meteor Crater" It suggests a NW direction of travel... is this correct? And how do we know? Does the "underthrust displacement" imply that the impactor was traveling from the SE toward the NW? Eric On 9/10/2010 8:05 AM, Kashuba wrote: Eric, Bernd, Sterling, List, David Kring of LPL put together a great guidebook for the 2007 MetSoc tour of the crater (150 pages). He is Gene Shoemakers successor as advisor to the Barringer family. He and family members lead the tour. Carolyn Shoemaker was there too. Chapter 9. "Trajectory" begins and ends thusly: The trajectory of the impacting asteroid is another issue of considerable debate and still unresolved. Historically, circular plan views of impact craters confounded many investigators who assumed a circular crater requires a vertical impact. They wondered why more craters are not elliptical. Gilbert and Barringer both realized that 45 degree impacts are the most probable trajectories for meteoritic material. Yet Gilbert, like many of his contemporaries, mistakenly thought a 45 degree impact produces an oval crater (Hoyt, 1987). Barringer, on the other hand, realized that a 45 degree impact will produce a round crater (Hoyt, 1987). Despite this insight, Barringer, like Gilbert, initially assumed that the northern Arizona impact had been vertical or nearly vertical and that the asteroid was buried beneath the center of the crater floor. When extensive drilling did not locate a main mass beneath the crater floor and instead only produced traces of the projectile, Barringer began to consider other options. He had already noted several features that seem to have a directional symmetry. - snip - More recently, techniques similar to those of Sutton were applied by Holliday et al. (2005) to the Odessa impact site. They estimated the Odessa craters were produced approximately 63,000 years ago. Although the ages of Barringer and Odessa craters are still not precisely known, these approximate ages suggest Odessa formed earlier, with the caveat that the Barringer crater may be older than 49,000 yrs. (See discussion in Chapter 11). Thus, the two impact events may not be directly related and may not have any bearing on the issue of trajectory. Nonetheless, several other potential indicators of trajectory survive (and even the Odessa connection might be revived). Unfortunately, these indicators cannot be reconciled at the present time and I think it fair to conclude that the trajectory of the impacting asteroid that produced Barringer Crater remains uncertain. Chapter 9: http://www.lpi.usra.edu/publications/books/barringer_crater_guidebook/chapte r_9.pdf Whole "guidebook": http://www.lpi.usra.edu/publications/books/barringer_crater_guidebook/index. shtml Regards, - John Ontario, California -Original Message- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of bernd.pa...@paulinet.de Sent: Friday, September 10, 2010 3:26 AM To: Meteorite-list@meteoritecentral.com Subject: [meteorite-list] Meteor Crater Shape and Entry Angle Eric wrote: "The crater is not perfectly round as would be expected from an impactor coming in at a sharper angle. In fact the crater is more elliptical in shape." SHOEMAKER E.M. and KIEFFER S.W. (1974, 1979) Guidebook to the Geology of Meteor Crater, Arizona (Publ. No. 17, Center for Meteorite Studies, Arizona State University, Tempe, Arizona): "Regional jointing has controlled the shape of the crater, which is somewhat squarish in outline; the diagonals of the "square" coincide with the trend of the two main sets of joints. The largest tears occur in the "corners" of the crater." Eric also inquired: "What would a "relatively low" impact angle be? 10 degrees, 20 degrees?" I tried to find more precise information on that but was unable to find something that might be of help here. Maybe someone else can shed more light on this! Regards, Bernd __
Re: [meteorite-list] Meteor Crater Shape and Entry Angle
To produce an elongated crater you need a very low angle impact, on the order of only a few degrees at most. Here's a quick, but more detailed answer. Additional searches will allow reader to find explanations with as much detail (and math) as they would like. http://www.scientificamerican.com/article.cfm?id=why-are-impact-craters-al -- Richard Kowalski Full Moon Photography IMCA #1081 --- On Fri, 9/10/10, bernd.pa...@paulinet.de wrote: > From: bernd.pa...@paulinet.de > Subject: [meteorite-list] Meteor Crater Shape and Entry Angle > To: Meteorite-list@meteoritecentral.com > Date: Friday, September 10, 2010, 3:25 AM > Eric wrote: > > "The crater is not perfectly round as would be expected > from an impactor > coming in at a sharper angle. In fact the crater is more > elliptical in shape." > > SHOEMAKER E.M. and KIEFFER S.W. (1974, 1979) Guidebook to > the > Geology of Meteor Crater, Arizona (Publ. No. 17, Center for > Meteorite > Studies, Arizona State University, Tempe, Arizona): > > "Regional jointing has controlled the shape of the crater, > which is somewhat > squarish in outline; the diagonals of the "square" coincide > with the trend of the > two main sets of joints. The largest tears occur in the > "corners" of the crater." > > Eric also inquired: > > "What would a "relatively low" impact angle be? 10 degrees, > 20 degrees?" > > I tried to find more precise information on that but was > unable to find something > that might be of help here. Maybe someone else can shed > more light on this! > > Regards, > > Bernd > > __ > Visit the Archives at > http://www.meteoritecentral.com/mailing-list-archives.html > Meteorite-list mailing list > Meteorite-list@meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list > __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
Re: [meteorite-list] Meteor Crater Shape and Entry Angle
Eric, Bernd, Sterling, List, David Kring of LPL put together a great guidebook for the 2007 MetSoc tour of the crater (150 pages). He is Gene Shoemakers successor as advisor to the Barringer family. He and family members lead the tour. Carolyn Shoemaker was there too. Chapter 9. "Trajectory" begins and ends thusly: The trajectory of the impacting asteroid is another issue of considerable debate and still unresolved. Historically, circular plan views of impact craters confounded many investigators who assumed a circular crater requires a vertical impact. They wondered why more craters are not elliptical. Gilbert and Barringer both realized that 45 degree impacts are the most probable trajectories for meteoritic material. Yet Gilbert, like many of his contemporaries, mistakenly thought a 45 degree impact produces an oval crater (Hoyt, 1987). Barringer, on the other hand, realized that a 45 degree impact will produce a round crater (Hoyt, 1987). Despite this insight, Barringer, like Gilbert, initially assumed that the northern Arizona impact had been vertical or nearly vertical and that the asteroid was buried beneath the center of the crater floor. When extensive drilling did not locate a main mass beneath the crater floor and instead only produced traces of the projectile, Barringer began to consider other options. He had already noted several features that seem to have a directional symmetry. - snip - More recently, techniques similar to those of Sutton were applied by Holliday et al. (2005) to the Odessa impact site. They estimated the Odessa craters were produced approximately 63,000 years ago. Although the ages of Barringer and Odessa craters are still not precisely known, these approximate ages suggest Odessa formed earlier, with the caveat that the Barringer crater may be older than 49,000 yrs. (See discussion in Chapter 11). Thus, the two impact events may not be directly related and may not have any bearing on the issue of trajectory. Nonetheless, several other potential indicators of trajectory survive (and even the Odessa connection might be revived). Unfortunately, these indicators cannot be reconciled at the present time and I think it fair to conclude that the trajectory of the impacting asteroid that produced Barringer Crater remains uncertain. Chapter 9: http://www.lpi.usra.edu/publications/books/barringer_crater_guidebook/chapte r_9.pdf Whole "guidebook": http://www.lpi.usra.edu/publications/books/barringer_crater_guidebook/index. shtml Regards, - John Ontario, California -Original Message- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of bernd.pa...@paulinet.de Sent: Friday, September 10, 2010 3:26 AM To: Meteorite-list@meteoritecentral.com Subject: [meteorite-list] Meteor Crater Shape and Entry Angle Eric wrote: "The crater is not perfectly round as would be expected from an impactor coming in at a sharper angle. In fact the crater is more elliptical in shape." SHOEMAKER E.M. and KIEFFER S.W. (1974, 1979) Guidebook to the Geology of Meteor Crater, Arizona (Publ. No. 17, Center for Meteorite Studies, Arizona State University, Tempe, Arizona): "Regional jointing has controlled the shape of the crater, which is somewhat squarish in outline; the diagonals of the "square" coincide with the trend of the two main sets of joints. The largest tears occur in the "corners" of the crater." Eric also inquired: "What would a "relatively low" impact angle be? 10 degrees, 20 degrees?" I tried to find more precise information on that but was unable to find something that might be of help here. Maybe someone else can shed more light on this! Regards, Bernd __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
[meteorite-list] Meteor Crater Shape and Entry Angle
Eric wrote: "The crater is not perfectly round as would be expected from an impactor coming in at a sharper angle. In fact the crater is more elliptical in shape." SHOEMAKER E.M. and KIEFFER S.W. (1974, 1979) Guidebook to the Geology of Meteor Crater, Arizona (Publ. No. 17, Center for Meteorite Studies, Arizona State University, Tempe, Arizona): "Regional jointing has controlled the shape of the crater, which is somewhat squarish in outline; the diagonals of the "square" coincide with the trend of the two main sets of joints. The largest tears occur in the "corners" of the crater." Eric also inquired: "What would a "relatively low" impact angle be? 10 degrees, 20 degrees?" I tried to find more precise information on that but was unable to find something that might be of help here. Maybe someone else can shed more light on this! Regards, Bernd __ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
