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Meteor Craters
Morning All
Every time I see a picture of the Lunar/Martian /other landscapes they are dotted with meteor craters - understandable. The point I have difficulty understanding is that all the craters are perfectly circular, implying that the object creating the crater arrived perpendicular to the surface. I can accept a number of them doing so but find it hard to believe no meteor/asteroid or whatever came in at a low trajectory so that it 'gouged' the surface. (Much like a plane crash on landing does) Surely the gravitational pull of the planet is not so strong that it overcomes the velocity of the meteors every time to cause them to crash perpendicular to the surface instead of, say, 10 or 20 degrees above horizontal. Curious Phil |
#2
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Hi Phil,
You are right, the gravity is not enough to change the trajectory to vertical. But the crater will be circular regardless of the trajectory, unless it is *extremely* low trajectory. The reason is the crater is not made by material being pushed out by the motion of the impactor. Instead, the kinetic energy results it acting as a large underground bomb. Imagine an underground railroad track. Now put a huge bomb on one of the cars. The resultant explosion will make a circular crater, even if the train is moving rapidly. This was confirmed by hypervelocity pellets fired at materials at various angles. Of course, as the angle gets low enough, there is a change. The first and biggest change is in the scatter pattern of rays. For example, if you look at a rectified view of Tycho (shifted so you are directly overhead Tycho), you will see the ray pattern is not symmetrical. The same is true for Proclus. Messier is an extreme example. And if you look around on the moon, you will find others where the craters are elongated. But in summary, all that kinetic energy is converted at an instant and acts like a huge bomb which almost always results in a largely circular crater. Hope this helps. Chuck Taylor Do you observe the moon? Try http://groups.yahoo.com/group/lunar-observing/ Are you interested in understanding optics? Try http://groups.yahoo.com/group/ATM_Optics_Software/ ************************************ "Phil Hawkins" wrote in message news Morning All Every time I see a picture of the Lunar/Martian /other landscapes they are dotted with meteor craters - understandable. The point I have difficulty understanding is that all the craters are perfectly circular, implying that the object creating the crater arrived perpendicular to the surface. I can accept a number of them doing so but find it hard to believe no meteor/asteroid or whatever came in at a low trajectory so that it 'gouged' the surface. (Much like a plane crash on landing does) Surely the gravitational pull of the planet is not so strong that it overcomes the velocity of the meteors every time to cause them to crash perpendicular to the surface instead of, say, 10 or 20 degrees above horizontal. Curious Phil |
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On Thu, 24 Feb 2005 20:06:44 GMT, Phil Hawkins
wrote: Morning All Every time I see a picture of the Lunar/Martian /other landscapes they are dotted with meteor craters - understandable. The point I have difficulty understanding is that all the craters are perfectly circular, implying that the object creating the crater arrived perpendicular to the surface. I can accept a number of them doing so but find it hard to believe no meteor/asteroid or whatever came in at a low trajectory so that it 'gouged' the surface. (Much like a plane crash on landing does) True, most are circular, but there are exceptions. When an object strikes the surface at very high velocity, the resulting impact will always be circular except for impactors that arrive at very shallow angles. The distribution of circular to oval craters on the Moon does match what you would expect for objects arriving from random directions. Surely the gravitational pull of the planet is not so strong that it overcomes the velocity of the meteors every time to cause them to crash perpendicular to the surface instead of, say, 10 or 20 degrees above horizontal. It isn't. Large impactors are only slightly deflected by gravity. _________________________________________________ Chris L Peterson Cloudbait Observatory http://www.cloudbait.com |
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CLT wrote:
snip Thanks Chuck, It does help. I can understand it now Regards Phil |
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snip
Thanks Chris Chuck and yourself have answered my question (I was worried that all the Astronomers had 'left the building' grin) Regards Phil |
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"Phil Hawkins" wrote in message
... snip Thanks Chris Chuck and yourself have answered my question (I was worried that all the Astronomers had 'left the building' grin) LOL! Elvis is still in the building. Of course, if you sit down to watch the politics raving movies, keep on eye on Chris, or he'll eat all your popcorn. ;-) Chuck Taylor Do you observe the moon? Try http://groups.yahoo.com/group/lunar-observing/ Are you interested in understanding optics? Try http://groups.yahoo.com/group/ATM_Optics_Software/ ************************************ |
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Phil Hawkins wrote:
Morning All Every time I see a picture of the Lunar/Martian /other landscapes they are dotted with meteor craters - understandable. The point I have difficulty understanding is that all the craters are perfectly circular, implying that the object creating the crater arrived perpendicular to the surface. I can accept a number of them doing so but find it hard to believe no meteor/asteroid or whatever came in at a low trajectory so that it 'gouged' the surface. (Much like a plane crash on landing does) Surely the gravitational pull of the planet is not so strong that it overcomes the velocity of the meteors every time to cause them to crash perpendicular to the surface instead of, say, 10 or 20 degrees above horizontal. Curious Phil I always wondered about that myself until I was watching some Science Channel programs were a researcher was looking into the phenominum himself. Using a high speed cannon he blasted craters in piles of sand (?) at various angles. The resulting craters were in fact circular no matter the angle of strike. Dave N. |
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"Phil Hawkins" wrote in message ... snip Thanks Chris Chuck and yourself have answered my question Chris has a bad habit of doing that. Seems he just needs to heard too |
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CLT wrote:
snip Elvis is still in the building. Of course, if you sit down to watch the politics raving movies, keep on eye on Chris, or he'll eat all your popcorn. He can have my popcorn Just leave my beer and nuts alone!!!! ;-) snip |
#10
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"Mike" wrote in message
news:vyvTd.3678$ab2.1002@edtnps89... "Phil Hawkins" wrote in message ... snip Thanks Chris Chuck and yourself have answered my question Chris has a bad habit of doing that. Seems he just needs to heard too I'm not sure what you meant. Did you mean: (1) Chris writes clear answers that are consistently accurate, and shares his knowledge with others? or (2) Chris writes posts that are grammatically correct and make sense, unlike your post above? I'm sure you didn't mean: (3) Chris answered a question after it had already been answered. The reason I'm sure you didn't mean #3 is that this would display an ignorance of how newsgroups work. This is not like a Yahoo group or astromart forum where everyone receives the posts at the same time. A question is posted and that post migrates to various news servers. In this case, I received it and answered it before Chris saw it. Other people will receive only the question, even after I had answered it. They will receive the question, but not the answer(s) that have been posted to it. So they will in turn answer it, not knowing it has been answered. This is one reason you will see several answers to one question, even though the answers are nearly all the same. Of course, many of us (myself included) simply start at the top and work our way down. So we answer a question and do not discover until later it has already been answered. And as well, a third reason you will find different answers is that each person posting an answer will explain it a little differently. One may include a detail another omitted and vice versa. Or simply because it is described differently, one answer may make sense to the original questioner while another does not. Of course, I'm sure this isn't what you meant as it would display ignorance on your part. However if that is the case, reading posts by Chris and others will aid your education. Clear Skies Chuck Taylor Do you observe the moon? Try http://groups.yahoo.com/group/lunar-observing/ Are you interested in understanding optics? Try http://groups.yahoo.com/group/ATM_Optics_Software/ ************************************ |
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