For what it’s worth, it seems that there are more than a few doctoral dissertations on the impact effects and modeling of the Chicxulub impact, presumed in this paper: https://www.geo.arizona.edu/Antevs/Theses/GoldenPHD08.pdf to be about 10 km in diameter. You can skip ahead to page 161 for some of the discussion of the results of the model. This paper in particular challenges the earlier “global firestorm” presumptions, conclusions start on page 210, "Although a pulse above solar values for ~30 minutes and peaking at 6 kW/m2 , as predicted by our nominal Chicxulub model, is sufficient to cause significant dermal damage (even to large animals), this is below the lower limit for piloted ignition of most woody biomasses.”. 

The whole thing is probably a good read though, from skimming through it. 

On Dec 29, 2019, at 7:05 PM, Kurt Feltenberger <xxxxxx@thepaw.org> wrote:

Folks,

I'm trying to develop some backstory for a world that has had a societal collapse from several different threat vectors.  The world is very much Earthlike; consider it being similar size, hydro, etc. when the event happens.  It's just on the cusp of developing the J-Drive, Fusion, and M-Drive, so some of these things are already operating in some form of testbed.

A comet or meteor is discovered that will hit the planet and naturally after initial panic is over, they decide to try and destroy it with nuclear weapons.  The plan works...to a point.  The single object is destroyed, but now it's created a swam of smaller objects that will pass by/impact the planet over a two day period.

I recall reading a discussion on this list many years ago (pre 9/11/01?) about something similar and the effects that all the smaller objects would have.  IIRC, even if they didn't impact and cause significant damage, they would burn up in the atmosphere and raise the average temperature, the debris would linger in the atmosphere and potentially help cause a greenhouse effect, and I'm not sure what all else.

What would happen if only a few city killer sized objects made it through, but the majority of a large "planet killer" sized object burned up in the atmosphere over a couple days?

--
Kurt Feltenberger
xxxxxx@thepaw.org/xxxxxx@yahoo.com
“Before today, I was scared to live, after today, I'm scared I'm not living enough." - Me

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