Impacts Lead to Physics Problem
Image
Source
The above image is a detail of three distinct craters on
the asteroid Vesta, taken by NASA's Dawn spacecraft.[NASA] The
effects of impacts between larger planetary bodies and smaller
ones are usually presented as images such as this; sterile,
alien and as a permanent feature of whatever body happens to
be adorned with such scars. Though most of the crates in this
image (and there is very little space not showing an impact
crater) are likely a result of the initial accretion stages of
solar development, or the later Late Heavy Bombardment, many
of them will be relatively recent. We often link asteroids of
substantial size as artifacts of Earth's past or the subject
for unimpressive 90's action movies.
A little closer to home, this image is Meteor Crater,
Arizona and is a little over a kilometer wide, formed from an
impact 20k-50k years ago. Not exactly doomsday sized but
consider that the meteorite that created the crater is only 80
feet wide.[NEOP]
Most modern impacts are with very small rock type meteors,
which tend to burn up, or burst in the atmosphere.[Saito] The Shoemaker-Levy 9 comet
colliding with Jupiter 1994 brought the significance of rouge
hunks of mass moving through space into somewhat sharper
focus.