Mars Opportunity Rover (Courtesy of NASA)
Early missions simply flew by Mars, taking as many pictures as possible in the 1960s and early 1970s. Spacecraft then orbited Mars for longer studies as technology improved. The first mission to the planet's surface took place in 1976 when the two Viking landers made a successful touchdown and sent back images to Earth.
Parachuting to the surface, Pathfinder made a dramatic landing in a bouncing air bag in 1997. It carried a remote-controlled buggy called the Sojourner rover that analyzed chemicals in the Martian rock and soil. Twin rovers Spirit and Opportunity landed on opposite sides of the red planet in January 2004 on missions originally planned to last 90 days, but that are still ongoing.
In the spring of 2008, NASA's Phoenix Mars Lander safely touched down in Mars' north polar region. Launched in August 2007, Phoenix was the first in NASA's Scout program of small spacecraft. Phoenix was designed to study the history of water in the arctic soil and its potential for supporting life. Using a robotic arm to dig beneath the surface, the lander uncovered a layer of ice-rich soil and dug up samples for testing. Phoenix's onboard laboratories found clay, salts, and chalky minerals that could only have formed in liquid water. A laser instrument designed to study clouds detected snow falling from the Martian sky, the first time this has ever been seen. In November 2008, the Phoenix sent its last signals back to Earth, but scientists will be working for many years to continue studying all of the data sent back from Mars by the Phoenix mission.
Also in 2008, the Mars Reconnaissance Orbiter discovered an exciting clue about the planet's history. Scientists think that Mars was wet for a lot longer than they previously thought! Scientists have observed pictures sent back by the spacecraft and discovered a mineral called opal on the surface of Mars. Scientists know that opal only forms where liquid water is present. It is possible that if there was liquid water, Mars could have supported life. Scientists think the rocks that contain the opal minerals are about two billion years old. That means that there was liquid water on Mars two billion years ago. While that might seem like a long time ago, it is much more recent than scientists previously thought liquid water existed on Mars' surface.
Discover more Mars missions on NASA's Solar System Exploration website.
