|Vikings 1 and 2 became the first space probes to successfully land on the surface of Mars. Viking Lander 1 was the first U.S. spacecraft to successfully touch down on any planet other than Earth. Both spacecraft were launched in 1976, the year in which the United States celebrated its bicentennial. The Viking probes analyzed gases in the Martian atmosphere and chemicals in the soil for evidence of the existence of simple life. The probes also measured wind speed, wind direction, atmospheric temperature, and atmospheric pressure. The Viking orbiters mapped the Martian surface.|
On July 4, 1997, after a 7 month journey, Pathfinder entered the Martian atmosphere. Minutes later, its airbag-cocooned lander bounced to a stop on the Martian surface. The Pathfinder Lander, now known as the Sagan Memorial Station, carried onboard a robotic rover named Sojourner. The 10 kilogram solar-powered rover was equipped with a spectrometer used to analyze the chemical composition of Martian rock and a camera which relayed images of the landscape back to Earth. The Pathfinder lander and the Sojourner rover sent thousands of images, more than 15 analyses of Martian rocks and data on weather condition to scientists on Earth. The low-cost mission has been said to set the standard for 21st century space exploration.
As part of their mission to explore Mars, NASA launched twin robotic rovers on June 10 and July 7, 2003. For landing, each rover was encased in a beach ball - like apparatus with a parachute attached. After impact, the lander bounced along the Martian surface, eventually rolling to a stop. The airbag then deflated and retracted, exposing the rovers. Both rovers landed during the Martian afternoon while Earth was still in view. This allowed the rovers to communicate with Earth via the Deep Space Network, letting scientists know they had landed safely. The Network is a series of antennae located in California, Spain, and Australia; it allows the rovers to send scientific data to Earth and allows scientists on Earth to send commands to the rovers on Mars. The rovers, named Spirit and Opportunity, landed on the Martian surface approximately three weeks apart in January, 2004.
The rovers were sent with the specific goals of locating and examining soils and rocks that might hold clues to past water activity on Mars. The rovers landed in different regions of the planet. The landing sites were chosen because previous observations had suggested water activity in the areas. The rovers carry various scientific instruments that aid the scientists in their long distance exploration. The panoramic camera helps determine the texture and structure of the terrain. Spectrometers are used for analysis of soil, rock, and atmospheric samples. A microscopic imager is used to collect high resolution images of soil and rock particles. There is also a rock abrasion tool that removes weathered surfaces from rocks, exposing fresh materials for examination by the imager and spectrometers. The scientists move the rovers approximately 40 meters per day, examining the terrain as progress is made. The rovers were designed to last a minimum of 90 days on the Martian surface.
Spirit and Opportunity are solar powered. The longer they are on the surface, the thicker the layer of dust that collects on the solar panels, blocking out their power source. Also, as Mars continues on in its orbit, it temporarily moves farther away from the Sun, further decreasing the sunlight reaching the solar cells. Eventually the batteries will lose their ability to power the rover activities and telecommunications will be lost. As of January 1, 2009 the rovers are still in service.
So what have the two rovers found? Lots and lots of evidence that liquid water was once plentiful on the surface of Mars! Among this evidence, they have found crystals that only grow in the presence of water, and rock formations which could only have been carved by flowing liquid water.
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