While Mars rovers such as Curiosity, Spirit and Opportunity have provided important discoveries, There is only so much Mars a rover can see from the ground. A drone could let the us see further. NASA’s working on a small flying robot copter for a future Mars mission. Drones are proving themselves versatile on Earth, so it’s natural to think they might be useful on Mars too.
The biggest challenge: while Martian gravity is less than that of Earth, Martian atmosphere is a lot thinner. A fixed-wing scout plane on Mars would have to go fast to generate the kind of lift needed to stay airborne, which in turn would likely require prohibitive amounts of fuel or battery power. Instead, NASA is looking at a copter, with two spinning rotors going 2400 rpm.