Lifeforms on other planets will be even more varied than they are on this planet. They will depend to a large extent on the gravitational field on a planet which has a much higher gravity than Earth - obviously you couldn't have large animals - they'd be small and squat and perhaps with many legs. On the other hand, on planets with very low gravity you would have very spindly, thin animals - very tall ones - and trees perhaps hundreds of feet or hundreds of metres high and maybe even kilometres high. The variations we will find in space are almost infinite
