Mars is the fourth planet from the Sun, the next planet furthest out from Earth. It just barely missed being in the Goldilocks zone for our Sun by just a bit. At one time in its life (after forming from the planetary debris field), it had temporarily been able to support liquid water. This is why it is so interesting to us, because who knows what could have happened within that liquid water environment. This is all possible because the Sun, in its initial span of life, burned hotter and brighter than the Sun we know today, which is good, because it provides the third planet, our Earth, with just the right amount of energy to keep us from freezing solid or boiling all of our water away.