Safe and sound on Mars.

The U.S. is back on Mars. After a journey of seven months and 302 million miles, NASA's rover spacecraft Spirit touched down on the Martian surface on January 3. But the landing caused NASA scientists some anxious moments.

First, the 400-pound robot craft had to survive the fiery plunge through the Martian atmosphere. Then Spirit had to land and come to a precise half after bouncing and rolling around on the rocky plain for more than a mile. When it finally settled and transmitted its first strong, steady radio signals home, the scientists at NASA's Jet Propulsion Laboratory in Pasadena, California, burst into cheers.

"We hit the sweet spot," said Dr. Steven W. Squyres, the mission's principal science investigator. "We are in the place we absolutely wanted to be!"

In the days that followed, scientists were equally overjoyed at the high quality of the color photographs Spirit sent of the Mars surface.

Spirits mission is to study the planet's rocks and sediments for proof that Mars once had water. Finding evidence of water might mean that Mars could have supported life.

The Spirit mission is extremely important to NASA, which has not had a successful landing on Mars since 1997. In 1999, the agency sent a spacecraft to Mars, but it disappeared during landing.

Last month, President Bush announced his plan to send NASA astronauts back to the moon and to Mars. The President wants a human on the moon by 2020 and on Mars by 2030. "We choose to explore space," he said, "because doing so improves our lives and lifts our national spirit."