"It was about the size of a microwave oven," Jet Propulsion Laboratory engineer Jennifer Tosper says of Sojourner. "And if you look at the two Mars rovers, they're about the size of small cars."
CBS News Correspondent Jerry Bowen reports scientists call them the monster trucks of Mars rovers, equipped with an array of sophisticated hardware to look for signs of water and answer critical questions.
Among those questions, says Mars rover scientist Matt Golombek, are: "Did the climate change? Was it warmer and wetter in the past? Could life have started in the past?"
If all goes well, the rovers will make separate landings next January, parachuting to the surface in a protective cocoon of inflated air bags, and then come to life.
It will start roving to rocks targeted by ground controllers with a built-in navigation system designed to keep it out of trouble.
"It knows how to navigate around the rocks that are too big for it, and to go and reach that target," says test engineer Jessica Collisson. "So that at the end of the day, it can communicate back to us, and say, 'Yep, I made it. I'm here.'"
And once there, the robot geologist goes to work.
On earth, scientist Steve Squyres, says, "When we get up to a rock, we'll reach out with the arm. We'll use the rock abrasion tool to grind a hole into the rock, put the microscope down in that hole and take a close-up picture of the interior of the rock."
This $800 million mission has more riding on it than the two rovers. With the loss of two other Mars-bound spacecraft in 1999 and the grounded shuttle program, NASA is in need of a success story.
And it has company. Last Monday, the European Space Agency launched its Mars Express, another little lander looking for life on the red planet.