For starters, the way Curiosity will lower itself to the surface of Mars in less than 20 days is unprecedented. The rover will use a new and complex sky crane system to slow its descent.
According to Doug McCuistion, director of the Mars Exploration Program at NASA Headquarters, Curiosity's landing "could arguably be the most important event — most significant event — in the history of planetary exploration." [How Curiosity's Nail-Biting Landing Works (Pictures)]
Previous Mars rovers, such as the twin Spirit and Opportunity rovers (collectively known as the Mars Exploration Rovers), used airbags to cushion their landing. Spirit and Opportunity arrived at the Red Planet about three weeks apart in January 2004. Each rover weighs about 384 pounds (174 kilograms), but since Curiosity tips the scales at 1 ton, it was deemed too heavy and too large for an airbag-assisted landing.
"The mass of Spirit and Opportunity was just about at the limit for what that airbag design could handle," McCuistion said.
Spirit and Opportunity were designed for three-month missions on Mars, but both far outlived their warranties. After getting stuck in Martian sand and losing contact with Earth, Spirit was officially declared dead in May 2011. But, Opportunity is still alive and well, and is currently exploring a massive crater, called Endeavour. Since it landed on the Red Planet, Opportunity has logged an impressive 21.4 miles (34.4 km).