Gas Density of Lunar Crater Rims: Comet vs. Asteroid Impacts

[snorkack]

TL;DR Summary

Properties of vapour driving explosion

I mean - when they form.
What are typical gas densities at lunar crater rim when the crater is made by a comet? An asteroid?

Both a comet and an asteroid, hitting Moon at several km/s, initially heat up to several thousand K, and even asteroid produces some vapour... at hypocentre.

However, by the time a crater rim forms, the blast has spread out a lot. If a crater is 100 km in diametre, then throwing soil 50 km from the centre to the rim requires propelling the soil at 400 m/s... by the time crater rims are formed, the energy of explosion has been transmitted from a small amount of rock moving at several km/s to a large amount of soil moving a few hundred m/s. Which process would be accompanied by drop of temperature - and condensation of rock and iron vapour.

However, cometary ices would NOT be in any hurry to condense!
Does this cause comet craters on Moon to be very different from asteroid craters?
For example... on Earth, Venus and perhaps Mars, air is ahead of soil thrown out of crater. It follows that fine dust and sand in soil are slowed down by air, while boulders continue further, by inertia.

In contrast, on Moon what lies ahead is vacuum, and the steam is behind the soil. It follows that fine dust and sand should be accelerated more and blown further from the crater, while boulders should be left behind.
Are this kind of winnowing effects conspicuous on Moon?

 

[malawi_glenn]

Also by a "typical" object (asteroid, comet)?

The Moon has some atmosphere though, 0.3 nPa so its not vacuum (still better vacuum than most/all man made vaccuums)

 

[Drakkith]

While I can't answer your question, I found some promising papers that might help on arxiv: https://arxiv.org/search/?query=crater+formation+physics&searchtype=all&source=header

 

[256bits]

Summary: Properties of vapour driving explosion

Does this cause comet craters on Moon to be very different from asteroid craters?
For example... on Earth, Venus and perhaps Mars, air is ahead of soil thrown out of crater. It follows that fine dust and sand in soil are slowed down by air, while boulders continue further, by inertia.

In contrast, on Moon what lies ahead is vacuum, and the steam is behind the soil. It follows that fine dust and sand should be accelerated more and blown further from the crater, while boulders should be left behind.
Are this kind of winnowing effects conspicuous on Moon?

Strength of gravity, the presence of an atmosphere, as well as surface material strength would all play a part in the formation of the crater and ejecta. And of course, the yield strength of the incoming celestial body for atmospheric conditions - does the incoming body explode from the pressure wave within resulting from the drag force of the atmosphere somewhere above the surface, or stay relatively intact to produce a hypervelocity impact upon the surface ( in a no, or thin, atmosphere this would be the case ).
Since the mv^2 kinetic energy is huge, the release of that energy is of several atomic bombs strength.
In no atmospheric conditions, ejecta would be following a ballistic path,
In an atmospheric conditions, large ejecta would follow a more ballistic paths but still suffer from atmospheric drag. Smaller ejecta would probably go pyrothechnic-ish ( its ballistic trajectory ( velocity ) greatly reduced due to the atmosphere ) much the same way as from a volcano, and blanket the surrounding area for several crater radii ( I presume. )