The skies around Mars are expected to get busier soon, and traffic on the ground will increase, too. The United States, Europe and Japan are sending spacecraft and landers to give them a broader and closer view of the Red Planet. The European and Japanese craft are already on their way, and the first of two American probes is to go up Sunday. A major goal is to find water and life.
The frequency of earthly visits to Mars late this year and early next is no coincidence. The chief of space science at the U.S. space agency NASA, Ed Weiler, says Mars and Earth reach their closest point every 26 months, and this August, they will come closer than they have in nearly 60,000 years. "The celestial mechanics of the situation - that is, where Earth and Mars are in 2003, how much sunlight would be at the landing site - all those things added up to make 2003 a very, very good opportunity for surface science," explained Mr. Weiler.
NASA has been trying to get back to Martian soil since its successful 1997 landing mission. That one parachuted the Pathfinder lander down in a protective airbag, delivering a small rover that analyzed rocks and took stunning images of the terrain. NASA tried to repeat that success in 1999, but failed when it lost contact with a lander that used rockets to slow its descent. Months earlier, it had lost communications with an orbiter as it reached Mars.
To regain the momentum, the space agency is dispatching two new landers with bigger, more sophisticated rovers than the one that scoured Martian soil six years ago. "We are returning to Mars - this time in force with twins," said former NASA Mars program director, Scott Hubbard, who is now a member of the panel investigating the shuttle Columbia disaster.
"This is a chance to not only double our science but to do it for far less than twice the cost - in fact, about half the cost of developing the first mission," he said. In one sense, the two new U.S. Mars Explorers are dual recreations of the successful 1997 mission in that they are to float down and bounce to a landing and deploy two robotic rovers.
Doubling the mission enables NASA to bring the landers down on opposite sides of the Red Planet. They will extend panoramic cameras to let scientists select promising geological targets in areas where water is thought to have flowed.
But NASA researcher Jim Garvin says these are more capable rovers that can roam much farther than the one six years ago - up to one kilometer during the 90-day missions. For the first time, they will be able to steer themselves around obstacles without specific commands, and see rocks in much finer detail.
"Seeing the actual grains that make up the building blocks of the rocks for the first time is in itself a major discovery no matter what it shows," said Mr. Garvin. "We haven't seen the underbelly of Mars at the scale it's assembled at. So we'll be looking at those bits the way we geologists do."
NASA's strategy is to seek further evidence of Martian water in its effort to determine if microbial life ever existed there or still does. In the 1997 mission, the shapes, composition, and placement of rocks revealed clear signs of ancient water flows. Mr. Garvin noted that American satellites circling Mars have reinforced this data, detecting landforms and soil movement that could be evidence of underground water.
"This has shown us, I think, that our scientific strategy for Mars that is sometimes referred to as 'following the water' has been true, and we're going to stay the course. Dual surface mobile field explorers on the surface of Mars are, indeed, very consistent with that," he said.
A European Mars probe launched Monday on a Russian rocket has similar goals, but is technically more modest. A very small lander will separate from an orbiter and parachute to a cushioned landing. However, rather than roam, it will seek signs of life from a single location while the companion orbiter scans the planet with radar for underground water.
Japan's Nozomi mission, also set to arrive at Mars in December, has a different objective. As an orbiter only, it will study the red planet's thin atmosphere to determine why it has leaked into space and the impact solar radiation has had on the process.
Two-thirds of the more than 30 American and Russian missions to Mars since 1960 have failed. If all four U.S., European, and Japanese spacecraft arrive successfully this year, they will have beaten the odds.