When I first heard about them planning on using a helicopter on Mars, I thought it was a joke. Helicopter in Martian almost nonexistent atmosphere? But apparently they were serious and this is probably even more impressive than the rover itself.
It's
not an almost nonexistant atmoshere... It's an atmosphere of (virtually all) Carbon-Dioxide. THAT gas is heavier than the 'mix' we have here
on Earth. (Let off CO2 extinguishers here, and it stays low to the ground). Therefore it is denser. Now, yes, Mars is smaller than Earth, and so the
Gravity on Mars is less, and it's the amount of Gravity (as well as the depth of atmosphere!) that determines the ground Pressure, and the resultant
effectiveness of such a 'rotating-wing'. However, the lower Gravity also means that the downward thrust that is required for lift, is much less!
In fact a 'helicopter' on Mars, would require much less Power/Lift/Weight ratios, than anything here on Earth...