Step-by-step explanation:
Ans 1 ) As the gravity of a planet increases, there will be increase in thickness of atmosphere around that planet. The gravitational force of the planets holds the bulks of molecules of atmosphere (as gas will need higher escape velocity).
Ans 2) Mars is the easier planets among all other planets in our solar system as it lies in habitable zone and it as a moderate gravity (where live can survive). Well, there's lot of resources too.
Thanks for asking