Comparing Curiosity with Spirit

Curiosity, at left in the artist's rendering here, is much larger than the Spirit/Opportunity generation. That extra size will let the new rover carry more instruments and what NASA promises will a bigger, stronger robotic arm. "The most important difference is that Spirit and Opportunity aren't analytical labs--they are more for observing. This newest rover will be performing a more comprehensive study of the Martian environment," NASA's Michael Meyer said in the October post.

Well, there is at least one other, rather notable difference: Curiosity will be nuclear-powered. The rover will draw its electricity from the heat generated by the radioactive decay of plutonium. NASA says that the radioisotope system will give Curiosity more ample and more consistent power than was the case for the solar-powered Spirit and Opportunity. The expected operational life span for Curiosity will be at least a full Martian year, or 687 Earth days.

This isn't the first time NASA will have packed plutonium in a spacecraft. That was the power source for the Viking landers, which visited Mars three decades ago, as well as for missions including Pioneer, Voyager, Galileo, Cassini, Ulysses, and New Horizons--in short, every spacecraft ever launched beyond Mars.