|MISSIONS TO MARS|
December 2, 1999
The Mars Polar Lander is the next in a series of missions to Mars conducted by American scientists. In the past, some missions sought orbital photography or climate analysis. Others, such as the Mars Pathfinder, actually landed on the red planet. The timeline below provides a look at the previous eight missions.
Launch Date: November 28, 1964
The Mariner 4 -- equipped with a television camera, solar plasma probe and other gear -- gave scientists their first glimpse of Mars at close range, erasing earlier theories that civilization might have once existed on the red planet. The spacecraft gathered images and data from a fly-by distance of 10,000 km, without actually landing on the surface.
MARINER 6 & 7
Scientists designed the Mariners 6 and 7 to explore the equator and southern hemisphere of Mars. This mission -- another fly-by -- revealed cratered deserts, collapsed ridges and other geologic features of the planet.
Launch Date: May 30, 1969
Mariner 9 became the first spacecraft to orbit another planet. For a year, the spacecraft circled Mars, photographing the planet's surface and analyzing the surrounding atmosphere. Photographs from Mariner 9 revealed gigantic volcanoes and canyons across the planet. Scientists also found signs of ancient riverbeds in Mars' dry landscape.
VIKING 1 & 2
With Mariner 9's findings, scientists wanted to know whether life had ever existed on the red planet. In 1975, they sent their first robotic spacecraft to land on Mars, called Viking 1. Three weeks later, they sent a partner spacecraft called Viking 2. The Vikings were known as "landers" and recorded the seasonal changes on Mars from a low-lying volcanic region. They also gave scientists their first images from the planet's surface.
Launch Date: September 25, 1992
The Mars Observer was the first mission launched to Mars since the Viking orbiter landing 17 years earlier. The Mars Observer would again orbit the planet -- instead of landing -- to map the surface and monitor the atmosphere during a full Martian year. Two days before entering the orbit of Mars, however, scientists lost contact with the spacecraft. The reason why is still unknown.
MARS GLOBAL SURVEYOR
Launch Date: November 7, 1996
Delayed another four years after the Mars Observer failure, scientists launched the Mars Global Surveyor. This spacecraft arrived successfully and gathered data regarding the planet's surface features, atmosphere and magnetic properties. The Mars Global Surveyor will become a communications satellite to relay information back to earth from future "landers."
Launch Date: December 4, 1996
The Mars Pathfinder Mission was launched in late 1996 to study the Martian atmosphere, weather and geology for future missions to Mars. The mission generated large amounts of public attention as the Pathfinder sent back spectacular images of the surface from its Sojourner Rover, a wheeled remote vehicle.
MARS CLIMATE ORBITER
Launch Date: December 11, 1998
The Mars Climate Orbiter -- designed for another atmospheric study -- entered the Martian orbit about 9 ½ months after launch. But, like the Mars Observer, this spacecraft was soon lost too. A peer review points to the mixing of English and metric units in critical spacecraft operation calculations. The Mars Climate Orbiter was not able to maneuver properly with the wrong numbers.