Scientists at Jet Propulsion Laboratory say Mars is a giant puzzle, but a picture of the planet is slowly emerging. The rover Spirit landed on Mars early this month and Opportunity will land Sunday. Scientists say although they've had trouble communicating with Spirit since Wednesday, these missions are still important early steps in planetary exploration.

Not everything will go smoothly on the two missions, says JPL Engineer Randii Wessen, but if things go mostly right, much can be learned from the two robotic geologists, the Mars exploration rovers, Opportunity and Spirit.

"For three months, these guys are going to be driving around, trying to piece together the history of Mars," he said.

The rover missions follow three years of intensive work, and earlier successes, and failures. Two thirds of all missions to Mars have not succeeded. The most dramatic disappointment was the loss of two spacecraft, the Mars Climate Orbiter and the Mars Polar Lander, in 1999.

Engineers and scientists have been thrilled with high-resolution pictures sent by Spirit. Project team members are anticipating close-up analysis of rock samples. Brett Lindenfeld of Alliance SpaceSystems helped design and build the robotic arm on the two rovers, which will conduct that analysis, and says he felt exhilarated to see the arm in action.

"I've used this word a lot lately, but it's all been a little surreal. It's very rare that you see your hardware that you've paid so much attention to and worked so hard on, and you see it actually on another planet, with you're own eyes. It's a pretty special feeling," he said.

A 14-year-old student from Hyderabad, India, named Vignan Pattamatta, is also getting a special view of the project. Along with 15 other students, he is spending a week on the rover mission after winning a contest. He worked for three months on an essay on to become one of the winners. He says space exploration can answer the question: Are we alone in the cosmos?

"In Hyderabad, we actually took this contest very seriously," he said, "and an organization called the Hyderabad Planetary Society had conducted a briefing session: 'Students, this is what you're supposed to do in this contest, and if you're selected, you'll get to go to JPL and work along with the scientists of JPL.' Oh, [I thought] this is exciting. OK!"

Space scientist Candice Hansen is part of the mission team for the Mars Reconnaissance Orbiter, which is scheduled for launch in 2005. The craft will use a high-resolution camera to map Martian surface features. She says this is serious science, but adds that space exploration brings out the child in all of us.

"Children are so curious," she said. "My child asks me a million questions a day - why, why, why, why? And in a way, exploring another planet is us being children. We are exploring still. We are learning still. We are curious too. We are big, curious grownups."

Mars rover mission manager Jennifer Trosper says she views Spirit, the rover that she works with, as if it were a child. "This rover, I talk about it like it's a young teenager," she said. "It needs a lot of care. And I have a four-year-old stepson as well and I'll say, I need to go take care of the rover. The rover needs attention right now."

JPL engineer Randel Lindemann says engineers and scientists are slowly mastering the rover as they work with it. "Everything that we do with the rover that is new is a learning experience, to find out not only how the rover will perform, but how the communications link, how the software that runs on the rover and the software that runs on the ground and the software that talks between these two pieces of software, how all these things need to come together," he said.

Louis Friedman of the Planetary Society, a private organization that promotes space research, sees extraordinary excitement in the science community because of the Mars missions, and because of a recent statement by President George W. Bush. Mr. Bush announced plans to put humans back on the moon between the year of 2015 and 2020, and to use the moon as a base to visit Mars and other planets.

"We've got the president of the United States saying this isn't enough," he said. "We've got to send people there. Yeah, we're going to argue about details all the time, and my favorite vehicle won't be somebody else's favorite vehicle, and the pace won't be good enough for somebody and somebody else will think we're doing it too fast. Whether we should spend this much or 10 percent more or 10 percent less will be debated and argued, and it should be. But to me the principles are very, very exciting. We're on Mars. We're going to send people there. We're going to do it with the whole world. And we're going to explore the whole solar system. It's a great time to be alive."

JPL engineer Randii Wessen says the return to manned space flights is exciting. "But it needs real schedules, real funding, and a real commitment. And we'll see," he said.

Ambitious plans remain in place for the unmanned space program. The spacecraft Cassini will start to orbit Saturn in July this year. Other future missions include the Mars lander Phoenix in 2007, and an unmanned Mars science laboratory in 2009.