X-Message-Number: 19284 From: "George Smith" <> References: <> Subject: Why the moon has round craters. Date: Sat, 15 Jun 2002 11:08:46 -0700 Apparently no one knows. Here are the two examples posted yesterday to offer why the moon (and most known astronomical bodies) have almost universal circular "impact craters". (1) In Message #19280 Damien Broderick wrote in part > Of course there is, George, and even a child can test it. Go and make a > sand pit. Throw marbles at it from angles ranging from vertical to oblique. > At almost every trajectory, the crater is circular. > > As google said after about 10 seconds, > > http://cse.ssl.berkeley.edu/AtHomeAstronomy/activity_05.html > > >The results of this test are often very > > surprising. One would normally expect the > > crater to have an oblong shape on extremely > > wide-angle impacts. In fact, all craters that > > we have seen on the Moon and Earth are > > pretty much circular. The reason is that an > > explosion occurs on impact and the forces > > associated with an explosion are always > > spherically symmetrical. > (Well, perhaps we should ignore the butterfly patterns generated by nuclear explosions. Not spherical at all. Oh well). I see. If only marbles were being dropped on the moon everything would be just fine. God ... I mean, Newton would be in his heaven and all would be right with the world. But something "felt" wrong about giant marbles dropped on the moon from the hand of God or Newton or a child. Maybe it was from years of experience from seeing the results of high impact projectiles as well as explosions. So I went out into the real world and discovered that if I substituted high velocity bullets and various surfaces from a celestial body (the Earth) for a sandbox and marbles what I actually see are ELLIPTICAL craters. Didn't matter if I used .22LR rounds from my Smith & Wesson or .22 magnum cartridges from a North American minirevolver or .45 rounds from a Colt Combat Commander or 12 gauge solid slugs from my Remington Model 870 Wingmaster pump shotgun. Not one single circular crater unless I shot at a precise right angle into a clay cliff wall. But what about the "explosion" explanation? (2) In Message #19277 Magnus Redin wrote in part: > That was an easy one. The impacting bodies hits the moon with many > km/s. The sudden breaking when the moons surface is hit releases this > large ammount of energy and vaporises the impacting body along with a > part of the moon. This ball of gas and plasma expands in all > directions, not only in the direction the impacting body hit the > surface. > My high velocity projectiles were not exploding on impact. Not having access to a grenade launcher I decided I would ask a friend (a physicist who asked to not be named) about that part of the story and forwarded him the email. Here is part of what he wrote back to me: "This explanation defies the Law of Conservation of Momentum. If a rock hits the Moon so fast that it vaporizes both itself and a piece of the Moon, then it has so much momentum that hardly ANY of the resulting gas and plasma would go "backwards." His explanation would work were the craters all PARABOLAE (that is, curved cones). The vapor and plasma would expand rapidly due to the lack of atmosphere, yes, but the intense momentum transmitted to the fluid mass would project it in one specific direction, resulting in kind of a spreading blast "forward" (relative to the trajectory of the impacting body). "So what if the fluid mass expands so rapidly that it dissipates, or - horror of horrors - manages to look practically indistinguishable from a circle? Well, what we're talking about here is debris. That would explain why the circular edges of the craters are raised, and where all that lunar dust comes from. However, the impact crater itself would be lopsided - an ellipse - because the original impact came in at an angle. The momentum has to go SOMEWHERE, and if it goes into the rock "in front of" the incoming projectile, then more of that part of the crater will be vaporized than the stuff "behind" the projectile. His explanation works if and only if you break the laws of physics. "Furthermore, the last I checked, the BOILING point of rock is pretty high. The immense pressure of the entire Earth on its core fails to do anything more than melt it. Last I checked, what vapor that comes out of a volcano does NOT cool down to become lava elsewhere! The amount of energy this fellow is suggesting impacting bodies have is comparable to that of an atomic explosion. And that's just to vaporize the rock; turning it into PLASMA is an entirely new game! "Suppose, though, that for some magical reason nearly all impacting bodies that have ever hit the Moon have had more than nuclear bomb levels of kinetic energy. Not all of the rock would vaporize; some of it would just melt, particularly around the edges, and immediately underneath the vaporized material. That would tend to fill up the craters - not completely, mind you, but they would look like someone went over them with sandpaper. Furthermore, you would expect that the areas of the Moon immediately around the craters would be smoother than the parts away from any craters. As far as I know, this is not the case. "In short, this fellow doesn't know what he's talking about and probably doesn't realize it." Of course, my entire initial posting was to underline the fact that the current crop of lock step true believers still don't get it. They stand on the shoulders of dead midgets. They don't WANT to check their facts. They know they do not need to. Given enough time, reality will beat to death the most beautiful beliefs which do not account for the facts. Given enough time even the most stubborn dogmatist will pass away and be replaced by others hopefully less dogmatic. I fully expect to be there to see it all happen. Why does the Moon have round craters? Apparently no one really knows. Just my opinion ... and the Moon's. George Smith CI Member and Immortalist Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=19284