What could happen if a small planet-sized rock would collide with the earth?
Earth has survived for 4 billion years without meeting a planet-sized rock. Why should it happen now. You obviously have little concept of scale. The rocks that NASA plots, called NEO’s (Near-Earth Objects) are generally of the size a few meters across to several kilometers. None are planetary in size. However, it only takes a rock (asteroid) of ONE kilometer or more to threaten civilisation, and 5 kms to cause extinctions. None of these actually affect the integrity of the solid Earth. People (and I bet you) find it hard to conceive that we live in a thin gaseous envelope – and that is what is threatened by the common rocks flying around us. However, the number of objects drops off with the size, so that a planetary sized object may not even approach closer than the moon in the next 10 billion years, and we will have been swalloed by the sun before then. A planetary-sized object would affect the integrity of the solid Earth, but life would be extinguished before it actually hit. Don’t
