The Mars missions have involved three basic stages. The most primitive were the initial flyby missions. These were followed by orbiters and finally by lander and rovers. In 2009, the orbiters and rovers are both still active on the planet collecting data for scientists on Earth to study.
The first types of Mars missions were flybys. These very early craft included Mariners 3, 4, 6, and 7. These aircraft literally flew by the planet, taking pictures as they went by. These pictures were the first close-up shots of a planet ever taken. They showed impact craters similar to the moon and showed that the lines seen from Earth were not the canals that some had believed they were.
Orbiters were sent to Mars as technology advanced. These included Mariner 8 and 9, Viking 1 and 2, Mars Observer, Mars Global Surveyor, Mars Climate Orbiter, 2001 Mars Odyssey, Mars Express, and the Mars Reconnaissance Orbiter. As of 2009, the Odyssey and Reconnaissance Orbiters were still consistently sending back information. They have shown signs of caves, glaciers, and salt deposits on Mars, while the Gamma Ray evidence has pointed to the possibility of oceans on Mars at one point. The European Mars Express has shown similar findings.
Finally, the Mars missions advanced to landers and rovers that were sent to the surface of the planet for "hands on" exploration. These include Viking 1-2, Pathfinder, Polar Lander/Deep Space 2, Mars Exploration Rovers, and Phoenix. Under the control of the National Aeronautics and Space Administration (NASA) scientists, the rovers move around the planet collecting data on key issues. Spirit and Opportunity are still going strong after five years. Although they are controlled from Earth, they are subject to the weather and changes on the surface of Mars.
As of early 2009, the latest of the Mars missions was the rover Phoenix. Phoenix landed in August of 2008 with the primary purpose geological in nature. It is intended to study the geology behind water on Mars, which in turn would help to understand climate changes. It is also tasked with discovering any potential habitat in the ice-soil boundary.
The future of Mars missions is boundless. NASA plans on sending airplanes and balloons to the surface to study with close up aerial views. Subsurface explorations will explore the geology of the planet and check for water or signs of previous life. The samples being collected by the rover missions will in time give scientists the opportunity to study rocks, soils, and the atmosphere of Mars from Earth.