Question: how do meteorites crash into planets

Daniel Parsons answered on 10 Nov 2014:

Meteorites are mostly fragments of small planets that were smashed by large collisions early in the history of the Solar System. These remnants are now in the Asteroid Belt, where many thousands of small objects endlessly circle the Sun, between Mars and Jupiter.
These fragments all knock into one another and some fly off into space. If their path crosses the Earth’s orbit they may eventually hit the Earth and fall to ground as meteorites.
Once on a collision course, how the crash into Earth (or other planets) depends on quite a few things. How big they are is very important. Small meteorites are slowed by friction with the Earth’s atmosphere (from over 10 kilometres every second to less than 10 metres per second such that the hole that they make when hitting ground is normally only a bit bigger that the meteorite itself. Howver, very large meteorites, of 100 tonnes or more are not slowed by the atmosphere anywhere near as much and they are still travelling so fast that they explode or vaporize on hitting the ground. This forms a massive crater that is much bigger than the actual meteorite. Immense volumes of Earth are blasted out from the explosion from an impact crater.
The dinosaurs were almost certainly pushed into extinction by the impact from a meteorite and there is evidence for this collision in a large 200 km diameter impact crater in Mexico. The explosion from the collision caused so much destruction, including massive global tsunamis, world-wide fires, and so much dust in the atmosphere it blocked out the sun for years. This caused significant climate change and killed the dinosaurs!