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

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/

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"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

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

CLT wrote:
snip
Thanks Chuck,
It does help. I can understand it now
Regards
Phil

snip
Thanks Chris
Chuck and yourself have answered my question

(I was worried that all the Astronomers had 'left the building' grin)

Regards
Phil

"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/

************************************

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.

"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

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

"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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