Toxic2040
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June 13, 2019, 09:29:58 PM



4 km wide comet?

Yeah, as I said, such really really big rocks are all discovered already. No surprises.


Whilst size does matter...mass is equally important imho.


Quote
4 SOME GEOPHYSICAL EXPECTATIONS

We consider here some broad-brush expectations arising from the encounter of a swarm of cometary debris impinging on a hemisphere of the Earth. To match the observations at the Boundary, the swarm model must be able to reproduce the observations of extensive conflagration on at least a continental scale, predict the high concentration of nanodiamonds, and account for the presence of apparently lunar material in the boundary layer.
4.1 Thermal effects

Wood subjected to a flux of radiant energy forumla will ignite within 1–20 s. While the whole-Earth encounter may take hours, the energy within any local horizon may be released overhead within a few seconds. Wildfires will thus be initiated over a land area say 5 per cent of the area of the Earth (that of North America, for example) if the meteoroid swarm deposits ∼1–20 × 1025 ergs during the encounter. At the extreme, we can assume an encounter speed v= 30 km s−1 and 100 per cent efficiency of conversion of kinetic to radiant energy in the upper atmosphere. Then, the required mass of swarm to yield a continent-wide conflagration is ∼2–40 × 1012 gm. If the radiant energy is an order of magnitude down on this (say with the most of the energy going into bulk motion of air before disintegration, slowing the bolides to say 10 km s−1), then one requires the Earth to intercept a mass ∼2–40 × 1013 gm which is in the range of the masses discussed in Section 3. In reality, this energy will be distributed over a large number of discrete areas corresponding to Tunguska-like fireballs. There is therefore an expectation of conflagration over at least continental scales following such an encounter. A similar figure is reached if one distributes say N epicentres each of 2 × 103 km2 of fire damage over 25 × 106 km2 of continent: then one requires N∼ 104 Tunguska-like impacts corresponding to an intercepted mass ∼5 × 1014 gm.


Just to be clear, I am not really disagreeing with you.. I think we have mapped 90%+ plus of these debris fields caused by either comets or NEO's intersecting orbits and/or collisions.

Its the ones we might have missed that are cause for worry. This is not hypothetical or fringe theories, there is hard evidence that these events have happened in the past and are likely to happen again in the future.

Should you spend your precious time worrying over such things?  Probably not, but I dont think it should be ignored either.