Martians beware. Here come the robot Earthlings.
Their forerunners temporarily set up shop 20 years ago this month when Viking 1 landed on July 20, 1976. Viking 2 followed on Sept. 3. Now the robots are coming again to set up continuing operations. It's the start of the most intensive exploration ever of another world.
Three spacecraft are due to head for Mars this fall. They're bringing along three surface stations, two soil penetrators, and a rover explorer vehicle. The United States Mars Global Surveyor will study the Red Planet from orbit. The US Pathfinder will travel on a bullet-like trajectory right to the planet's surface carrying one robot research station and the rover. Russia's Mars '96, which also will orbit Mars, carries the other two stations and the penetrators.
Planetary scientists want to really know the only other planet in the solar system they think has - or may once have had - even the remotest possibility of supporting life. So from now on, whenever Earth and Mars are favorably aligned for space travel, they hope to send their robots. That means more orbiters, landers, penetrators, and rovers arriving at Mars roughly every two years. And, by 2005, the explorers hope one of the robots will bring samples of Mars back to Earth.
Future missions are an international effort. No single nation can afford the massive exploration envisioned. The California Institute of Technology's Jet Propulsion Laboratory (JPL) in Pasadena, which manages the National Aeronautics and Space Administration's Mars program, calls international cooperation "the cornerstone" of Mars exploration.
NASA's Mars Global Surveyor carries a French-supplied radio to help relay data from the Russian landers and penetrators. The Mars Surveyor planned for 1998 will carry the first Russian instrument to fly on an American planetary craft. It's the beginning of the Mars Together cooperative program between Russia and the United States, which will include a variety of future joint projects.
Meanwhile, experts from 20 countries share in Russia's Mars '96 craft. Writing in The Planetary Report of the Pasadena-based Planetary Society, Vassili Moroz of the Russian Academy of Science's Space Research Institute notes that "the entire world planetary community is interested in the success of Mars '96."
Even the first wave of invading spacecraft promises major advances in scientists' knowledge of Mars. With these new data and the knowledge from earlier missions, "we're going to know what Mars is made of," at least roughly, says Donna Shirley, manager of the Mars exploration program office at the Jet Propulsion Laboratory.
She explains that two wide-angle cameras on the Global Surveyor orbiter will give the big picture by mapping the entire planet through changing seasons. A high resolution camera will give more detailed views of selected areas.
Using the cameras together with the orbiter's laser altimeter, researchers should "be able to really look at the topography of the planet," Dr. Shirley says. She adds that the orbiter will also collect "a lot of information" on how the atmosphere changes during the course of the Martian year, which is 687 Earth days long.
Down on the surface, the Pathfinder science station and rover will study atmosphere, rocks, and soil. The station will have a stereo imager and will work with the rover's imager to study surface-atmosphere interactions as small as a few centimeters. The bread-box-sized rover will be able to roll up to a rock and analyze what elements it contains. But this rover, named Sojourner, can't do chemical analysis. That job is left for the rover to be sent with the 1998 lander.
Pathfinder's landing site is Area Vallis. That's a location where a channel apparently caused by a catastrophic flood empties into Chryse Planitia, the Plain of Gold. It's about 500 miles from Viking 1. Mars geologists think that debris representative of a wide Martian region may be found there.
Meanwhile, Russia's Mars '96 orbiter, landers, and soil penetrators will gather data that complement the Surveyor-Pathfinder studies. The Viking landers found that Mars has a chemically reactive soil that destroys organic matter. The penetrators should reach below that surface activity. If traces of organic matter or water exist beneath the topsoil, they may find them.
These new data should ease scientists' disappointment over loss of the Mars Observer spacecraft that fell silent on Aug. 21, 1993, just prior to arrival at Mars. In fact, Mars Observer lives again in the sense that the Global Surveyor carries copies of five of the original Mars Observer experiments.
These new explorations are pursuing what Shirley calls "the three great themes of climate, life, and resources." That includes searching for water and other resources humans might need or that robot factories could use to make fuel for sending samples back to Earth.
Mars is cold. It is 1.52 times farther from the sun than is Earth. Its largely carbon-dioxide atmosphere, with a surface pressure only about 1/8,000th of that on Earth, is too thin hold in much heat. Mars temperatures range from 93 degrees Celsius below freezing to 13 degrees above. Liquid water can't exist on the surface now, even though dry channels indicate that it once flowed there. And without liquid water, there's little hope for organic life as we know it.
No Mars missions, including the Viking landers, have found any sign of life. Antarctic meteorites that apparently come from Mars show no signs of life either. If life exists now, it must be hidden deep underground or in other protected areas, perhaps where there may be volcanic heat and hot springs. The Mars missions will look for such places. But most scientists today have little hope of finding life.
Fossils are another matter. The prevailing view of early Mars is that the planet may once have had an arctic-like climate with lakes or other surface water where liquid water could exist. If even primitive life once evolved, traces of it may be found in old lake beds and sites of former hot springs. Such sites are possible exploration targets.
Shirley notes that, even if no living or fossil organisms are ever found, finding evidence of life-like chemistry would be important. Jack Farmer of the NASA Ames Research Center, at Moffet Field, Calif., says that even finding evidence of a prelife chemistry would be valuable. Geological processes have wiped out the record of that phase of life's evolution on Earth. If Mars, which has been less active geologically, preserves a record of such chemistry, it could fill an important gap for earthly biology.
Whether or not the Mars explorers will fulfill their ambitious plans depends partly on the willingness of participating governments to fund their contributions. Louis Friedman, executive director of the Planetary Society, keeps close tabs on the Russian program. He says that it seems on track for the launch of Mars '96. But beyond that, he says, no one - not even Russian space officials - can know what future funding will be.
NASA's Surveyor program, which envisions launches at every two-year opportunity through 2005, is currently in good shape, according to JPL's Dr. Shirley. It has the money for the 1996 missions. Future missions will be funded through the annual budget process.
Meanwhile, NASA teams continue planning future Mars missions. That includes studying what to do on Earth if Mars samples are ever brought here. With even the remote possibility that such samples contained alien organisms, NASA might have to file an environmental impact statement. Donald DeVincenzi, life sciences manager at NASA headquarters, says that could throw the prospect for a sample-return mission into the environmental political arena, with unpredictable results.
Planned Mars Missions
Nov. 6-25, 1996: US Mars Global Surveyor will survey Mars from orbit using copies of five of the instruments on the lost Mars Observer. The ship will carry French-built radio to relay data from US and Russian landers and soil penetrators on the Martian surface.
Nov. 11-22, 1996: Russian Mars craft will survey Mars from orbit. Carries two landers and two soil penetrators. The US and several European nations are participating.
Dec. 2-25, 1996: US Mars Pathfinder lander will make a direct flight to Martian surface with a small Sojourner rover vehicle.
Aug. 1998: Japanese Planet B orbiter to study Martian upper-atmospheric physics.
Dec. 1998: Mars Surveyor 98 orbiter will continue orbital surveys, carrying the first Russian instrument (an infrared sensor) ever to fly on a US planetary craft, beginning the US-Russian Mars Together cooperative program.
Jan. 1999: Mars Surveyor 98 lander will land near a Mars polar region, and will carry a stereo camera, two small soil penetrators, and a Russian laser-ranging instrument.
2001: Russian Mars 2001. Its mission, not fully defined, will include a rover and/or surface stations. Possible international participation. May be part of US-Russian Mars Together program.
US Mars Surveyor 01 orbiter will conduct science from orbit. May be part of Mars Together program.
US Mars Surveyor 01 lander. Mission to be defined.
2003: US Mars Surveyor 03. Mission to be defined. May include orbiter and lander.
2005: US Mars Surveyor 05. Mission to be defined. May include returning Mars samples to Earth, a possibility now under study.
*Note: Some missions are still in the early planning stage.