why are people interested in mars? (it's zillions of miles away)?

Scientists have a lot of good data on how Earth formed, but it's always good to have more. If they can add data from Mars to their mathematical model of the solar system, they can better understand how planets formed and make better predictions of what's going to happen.

Also, we want to know more about the environment so we can move there at some point. It's good to not have all your eggs in one basket.

Haha! I don't really know but I assume it's because it's not "zillions" of miles away and scientists believe that it may have been the only other planet in our solar system that may have once held life.

So therefore, if they have found evidence that Mars once had life, they want to figure out why life no longer exists on that planet and what we can do on earth so that we dont wind up like Mars.

Maybe they also think that Mars is likely to be habitable again (if it ever was)

Also, all other planet besides out own is mainly made up of gas.