Why is almost every solid surface in the solar system covered by craters?
Question:
Answer:
Because there were a lot of meteors falling, and there was a long time for them to do so. And for bodies that are not geologically active, no mechanism exists to wipe out the craters.
because almost every solid surface in the solar system is peppered with meteorites sooner or later in millions of years
Two reasons: first, all the solid bodies in the solar system were created by many small objects collifing and sticking together. Second, in the 4.5 billion years since they were formed, remaining loose junk flying around had been impacting the various objects. The few that have a small number of craters (Earth, Io, Europa, Titan) have extensive amounts of liquid which either fill in or cover the craters.
When the solar system first formed there were still a lot of loose asteroids and comets moving around. These gradually collided with other objects (planets and moons) until we got down to the solar system's present population of such objects, which is small enough that large impacts are rare. The result is that all the planets and moons were left covered with craters.
The only surfaces now that aren't covered with craters are the ones that have been reworked since that time period. Such as the basalt plains of the moon, which were filled in by lava, and the surfaces of Earth and Venus which are reworked by plate tectonics, volcanism, and (in Earth's case) water erosion.
They were all hit by meteorites and comets.
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