Yes, there are secondaries, and fragments, but you screen a huge number of primaries with an atmosphere. Remember that the number of small craters on an airless world increases as about the inverse square of size, so there are 4 times as many bodies with half the energy (and energy scales as the cube of radius or diameter, so that's 80% of the diameter)
As for thickness, you can do it with Amagads, which is the technical way, but for those of little brain like myself, I follow Torricelli:
He found that a closed water tube over 30' (10m) tall exceeded the capacity of the atmosphere to support the water column, and a vacuum developed. In this way, he measured the pressure of the atmosphere and the weight of an equivalent column (layer) of water - i.e. 10m.
On other planets, you have to correct for gravity, but it works pretty well.
In fact, what we're doing with the meteors is balancing masses of the impactor vs mass of atmosphere swept out by the incoming trajectory. So low angle impacts are more efficient in weeding out small bodies, for example.
Space/Science » in reply to crater sizes
re: crater sizes
The whole thread (52 posts)
- Bill Hartmann (Scientist, textbook/fiction Author, & Painter)
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- Hartmann's Travelers Guide to Mars
- re: Bill Hartmann (Scientist, textbook/fiction Author, & Painter)