Craters Caused by Thermonuclear Explosions
--- Impact Craters by Thermonuclear Explosion
Postby CharlesChandler» Tue Jan 15, 2013 6:10am
- I think that all of the perfectly circular craters are formed by thermonuclear explosions.
- The instantaneous temperatures and pressures in the impact of a rock even only a couple of meters across, but traveling at 70 km/s, will be sufficient for nuclear fusion.
- The craters are circular, instead of oblong, because they were caused by the relativistic ejecta from the fusion event, not the trajectory of the impacter.
- And there is nothing to be found of the meteor because it was all reduced to plasma by the explosion.
... A meteor will certainly be charged, having passed through the ionosphere, which is positively charged.
- But any net charge is always around the outside of an object, due to electrostatic repulsion.
- Discharging the potential might char the surface, but it isn't going to blow the thing apart.
- If you want an electrical explosion, the current has to pass through the center, like a transformer blowing up when struck by lightning, because the wires lead through the center.
- in a monolithic charged body, this shouldn't be possible.
- I did have one idea on the topic.
- A meteor coming in at an angle will start spinning, due to the pressure gradient in the air.
- For a meteor 1 km across the air pressure goes from about 1000 mb down to about 850 mb, so the air under the meteor is 15% more dense than the air above it.
- Hence there will be more friction on the bottom than on the top, and this will cause the meteor to "roll" across the air.
- Moving at 70 km/s would develop an extremely fast spin.
- And what do we know about charged objects that are spinning rapidly?
- They generate magnetic fields.
- So the meteor's powerful magnetic field might be deflecting charged particles towards its axis of rotation (parallel to the ground, and perpendicular to the direction of travel).
- Hence there might indeed be an electric current flowing through the meteor's center.
- But it isn't megalightning between the meteor and the ground.
- Rather, it's a self-induced current due to its extremely rapid rotation.
- Would this current be powerful enough to blow the meteor apart? I dunno. :D
- But the magnetic induction from a rapidly rotating object moving through the Earth's magnetic field at 70 km/s would be huge,
- and this would certainly get the current going through the meteor, while electrostatic potentials between the meteor and the ground would not.
... Hydrostatic pressure and electrostatic repulsion will both push outward.
- But the charge is on the outside, and assuming imperfect thermal conductivity, so is the heat.
- So this shouldn't cause an explosion, but rather, just some boiling or burning at the surface.
- To get an explosion, you need the repulsive forces on the inside, contained by inwardly directed forces on the outside.
... By the way, I read up on the Tunguska event.
- Interestingly, there wasn't just one explosion — there was a series of them, and some of the accounts mentioned that they occurred at regular intervals.
- In EM terms, I'd call this "sputtering".
... An electric current through the Tunguska impacter might have sputtered before finally blowing the thing apart.
.Q: If you think electric discharge blew up the Tunguska bolide, could not the same sort of electrical explosion occur when a bolide hits a planetoid's surface?
.CC: On impact with the surface, the thermalization of the momentum will be the dominant energy conversion.
.Q: How can large craters form on small asteroids, moons etc, without blowing them up?
- Thornhill has said that bolide impacts could not make large craters on small asteroids, or moons, because they would break them apart. Wouldn't that be true?
.CC: An iron-core asteroid getting hit by a bolide half its size wouldn't necessarily get destroyed in the process.
- Also, keep in mind that the size of the bolide and the size of the crater are two different things.
- If the crater was formed by a thermonuclear explosion, a 1 km crater might have been formed by a 1 m bolide, and the 10 km asteroid wouldn't necessarily get destroyed by something like that.
- Also, the flat bottom craters are suggestive of an explosive that had an easy time excavating the dust at the surface, but didn't leave a dent on the solid rock below the dust.
- So again, the impacter might have actually been extremely small.
--- Thermonuclear Mechanism --- Crater Central Peaks --- Shock Waves --- Meteor Explosions
Postby CharlesChandler» Fri Jan 18, 2013 4:38am
.Q: How does high velocity impact produce thermonuclear explosion?
.CC: Nuclear fusion requires extreme temperatures (to get particle collisions that break up the existing nuclei) and extreme pressures (to keep the pieces from going anywhere until they get a chance to clank back together into larger nuclei).
- In an impact, the momentum is thermalized, so there's the heat source.
- And until all of the momentum is thermalized, the remaining inertial force provides the pressure.
- And there is no theoretical limit to the amount of energy that can be stored in momentum.
- The velocity "might" be limited to the speed of light, but there is no limit on the amount of mass involved.
- So at least hypothetically, it's an easy reach to conclude that an impact would create the necessary temperatures and pressures for fusion.
- I'm satisfied that it's a hypothetical possibility, and that its properties match the observations.
.Q: How can central peaks contain strata like the surrounding bedrock?
.CC: This is a well-known fluid dynamic phenomenon, which would be an expected property of the ejecta from a thermonuclear explosion.
- When a high-velocity jet hits a perpendicular surface, it accomplishes little erosion where the jet is actually perpendicular.
- This is because there is nowhere for the fluid (i.e., nuclear ejecta) to go, so there is no excavation.
- Away from the normal point, the fluid can gouge out material and carry it off.
- So at the center of the crater, the only material that was removed was by simple vaporization.
- Away from the center, it's vaporization plus entrainment into the high velocity flow, which is more efficient at removing material.
- While on the topic of impacts, my "rolling electrodynamic meteor" epiphany hasn't fully satisfied me, and I kept thinking that I never actually fully answered webolife's questions, concerning a net charge that couldn't get fully neutralized fast enough, resulting in an electrostatic explosion.
- So I did some more thinking, and I came up with another epiphany.
- This concerns something that I have never fully understood about shock waves in front of supersonic objects.
- Why do [shock waves] get detached from the objects themselves, and stand off by quite a distance?
- By Newtonian standards, the shock front should never become "detached" from the object, and molecular rebounds should be fully absorbed in the first dozen collisions, producing an extremely thin buffer between the object and the oncoming air.
- Maybe the shock front isn't a fluid dynamic phenomenon, but an electrostatic one.
- High-velocity atoms in the approaching air are getting embedded in the boundary layer, stripped of their electrons, and therefore building up a positive double-layer around the supersonic object.
- The greater the speed, the thicker this positive double-layer, with electrostatic pressure pushing against the hydrostatic pressure of the oncoming air.
- For impacters getting into the thicker atmosphere, the implication is that this "detached positive double-layer shock front" might be highly charged, and therefore, might be responsible for an enormous amount of electrostatic repulsion within the supersonic object.
- In other words, if the meteor is surrounded by a layer of highly charged air, the air is going to suck all of the electrons out of the meteor.
- Then the whole thing will come unglued.
- The absence of valence electrons will weaken the crystal lattice of the solid object, and electrostatic repulsion will generate an outward force that wasn't there before.
- Once the meteor disintegrates into smaller pieces, the friction goes up exponentially, as that is a function of surface area, which is much greater for a bunch of small pieces than it was for one big piece.
- The increase in temperature adds hydrostatic pressure to the existing electrostatic pressure, and ba-boom!