ANN ARBOR—American science will return to the surface of Mars on July 4, after a 21-year absence, according to University of Michigan astronomer Richard Teske, when NASA’s Mars Pathfinder spacecraft enters the Martian atmosphere around 1 p.m. EDT.

“The spacecraft will first be braked by atmospheric friction, then by parachute and rockets, and finally bounce to a soft landing on air bags,” Teske said. “After turning itself right side up, if necessary, Pathfinder will open and deploy a mobile, wheeled robot called Sojourner, the first roving vehicle on Mars.”

The rover’s mission, intended to last seven Mars days, is to roam about analyzing the soils and rocks there, and take pictures of what it encounters. The non-moving Pathfinder will carry out its own months-long scientific program, taking color pictures of the landscape and relaying communications between Sojourner and Earth.

“Sojourner is the size of a six-wheeled desk drawer weighing 23 pounds on Earth and just over nine in Mars’ weaker gravity,” Teske said. The vehicle has the capability to climb in soft sand and scramble over rocks. Although operators on Earth will command the rover to go to specific locations selected from pictures made by Pathfinder, the rover will steer itself and decide on its own how to get to its assigned sites.

In addition to a camera, Sojourner has a small sensor, carried on its front like an elephant’s trunk, which it will use to determine the composition of materials on the surface. To analyze a sample, the rover will drive over, press the stethoscope-like device against the sample’s “chest,” and wait while automatic equipment makes the necessary measurements. Its camera helps operators on Earth position the sensor and gives close-up pictures of the sample being examined.

This is the first of a new series of landing probes, which will be sent every two years to explore Mars, although it’s the third time NASA has landed something on the planet. In 1976, two Viking spacecraft touched down on Mars. They sampled the soil and atmosphere, took pictures, and sent back a years-long record of the weather. Scientists now expect to extend the significant knowledge gained from those Vikings by making detailed studies of Mars’ surface at different locations.

“Pathfinder is targeted toward a region on Mars that promises to be especially revealing,” Teske explained. “We have clear photographic evidence that large areas of Mars experienced vast floods in the past, although no liquid water exists on the surface today. Planetary scientists want to know what caused the inundations and where the water went afterward. To help answer these questions, Pathfinder will land near the mouth of a giant dry outflow channel larger than the state of Michigan called ‘Ares Vallis.’ Located at a place corresponding to the latitude of Mexico City on Earth, the landing site shows abundant signs of past flooding.”

According to Teske, scientists won’t know initially exactly where the probe lands. “Pathfinder is to descend somewhere within a target oval whose length would stretch from Detroit to Kalamazoo and whose width is equal to the distance from Lansing to the Ohio/Indiana border,” he said. “But the lander’s operators expect that after several months of exchanging radio communication with it on Mars’ surface, they will be able to pinpoint its position to within an area the size of an average living room.”

One of Pathfinder’s tasks is gathering information on daily and seasonal meteorological variations. Another is assessing interactions between the atmosphere and surface.

Because erosion, transport and deposition of sand and dust by strong winds are important processes shaping Mars’ desert-dry landscape, Pathfinder is designed to observe them in action. It carries a system for measuring temperatures, air pressures and the direction and speed of winds at different elevations above ground. Other devices measure the amount and composition of wind-blown dust. A long series of stereo pictures will show how the dust piles up and gets blown away, and how weathering of rocks takes place. Pathfinder’s camera will peer down at Sojourner’s tracks in the dust and sand, allowing scientists to estimate mechanical properties of surface soils.

Scientists expect that some of the rocks Sojourner will examine may have been washed down from distant regions by ancient flood waters passing over the site. Thus the materials being analyzed could represent conditions from across a wide area of Mars. Finally, scientists will be alert for yet-unanticipated clues about the origin and disappearance of the waters that scoured Ares Vallis long ago. 

More information:

• Richard Teske
• Sojourner
• Ares Vallis
• pobo@umich.edu