The larger the planet, the longer it takes to cool. Earth and Venus have cooled the least, Mercury and the Moon the most. Mars is in between. The molten cores generate any magnetic field there may be. Venus hasn't ever had one and we don't know about Mercury.
Impact cratering When comet or asteroid crashes into the planet's surface, it leaves a crater.
See craters on all planets or bodies with a solid surface. The impact vaporizes the rock in the area it crashes into, and the meteor itself will be either vaporized or pulverized. Crater is circular and the debris that is kicked up during impact will cover a greater area than the hole itself. More small craters than large ones because more small meteors than large ones. Largest meteor craters are called impact basins .