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The two powerful new Mars rovers have far greater mobility than the 1997 Mars Pathfinder rover. These identical robotic explorers were originally thought to be able to trek up to 100 meters (about 100 yards) a day ("sol") across the martian surface, but on March 31, 2005 Opportunity traveled a distance of 220 meters (722 feet) in a single day. This is farther than the Sojourner rover's travel throughout its entire mission. Each rover carries a sophisticated set of instruments – the Athena Science Payload – that has allowed it to search for evidence of liquid water in the planet's past.

Mission Overview

On June 10, 2003, the first Mars Exploration Rover (MER) spacecraft Spirit was launched on a Delta II rocket from Cape Canaveral, Florida. After a seven month flight, it entered the martian atmosphere in January 3, 2004. The second lander and rover, Opportunity, followed on January 24. The rovers each had a spectacular landing, similar to that of the Pathfinder spacecraft. After entering the atmosphere, the rovers deployed their parachutes and airbags, hitting the surface with enough force to bounce back up a hundred feet in the martian air. After finally settling down, the lander petals opened to reveal the rovers folded inside like origami. The rovers had to unfold themselves carefully, deploying their camera masts, antennae, wheels, and solar arrays.

The landing portion of the mission featured a design that is dramatically different from that of Mars Pathfinder. Where Pathfinder had a lander and the small Sojourner rover, each MER spacecraft carried just a large, long-range rover. The rover has a mass of nearly 180 kilograms (about 380 pounds).

Each rover can take a 360-degree visible color and infrared image panorama. Athena scientists can choose rock and soil targets and command the rovers to explore their surroundings. The landers have long since been left behind, as both Spirit and Opportunity have searched out enticing clues in the soil. When a rover reaches a target, its multi-jointed arm deploys and the target is examined with a microscope and two spectrometers. The "RAT" (Rock Abrasion Tool) is used to expose fresh rock surfaces for study. Images and spectra of interesting rocks and soils are taken daily. It was originally believed that the rovers would only have the solar power capability to last for around 90 sols, or the early summer of 2004, but regular "cleaning events" and careful maneuvering have allowed them to continue to today.

Science Goals

One of the great mysteries of Mars comes from its marked similarity to Earth. Mars today is dry and cold, but whether this was always so, for how long Earth-like conditions persisted, and whether life ever developed has important implications for many fields, as well as simple curiosity. The mission therefore seeks to determine the history of climate and water at sites on Mars where conditions may once have been favorable to life. The landing sites at Gusev Crater and Meridiani Planum were selected on the basis of intensive study of orbital data collected by the Mars Global Surveyor spacecraft and other missions. These sites not only offer some evidence that liquid water was once present, they also have gentle enough terrain to permit safe landings, and ample light to permit solar power to drive the rovers. The rovers' scientific instruments are working to read the geologic record at each site, in order to investigate what role water played there, and to determine how suitable the conditions would have been for life.

As of this writing, both rovers have revealed substantial evidence for liquid water at some time in the past at both sites. Opportunity early on found evidence of hematite, a mineral formed mostly in the presence of water, rock formations bearing chemical evidence of long-term water habitation, and physical evidence of water-formed rocks. Spirit had more difficulty, but eventually found evidence for water near Husband Hill, one of the hills named in honor of the lost Columbia astronauts.

Both Spirit and Opportunity have contributed a great deal of knowledge to our understanding of Mars, with the rovers doing everything from geology to astronomy, snapping the first picture of Earth from another planet. Much of the data has yet to be analyzed, and will surely yield even more discoveries.

For more information on the study of Mars, check out the JPL website.

Mars Exploration Rovers Press Kit: Launch
Mars Exploration Rovers Press Kit: Landing


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