Mars Global Surveyor
Launch: November 7, 1996
Arrival: September 12, 1997
Launched November 7, 1996, Mars Global Surveyor became the first successful mission to the red planet in two decades. After a year and a half spent trimming its orbit from a looping ellipse to a circular track around the planet, the spacecraft began its prime mapping mission in March 1999. It has continued to observe the planet from a low-altitude, nearly polar orbit ever since.
The mission has studied the entire Martian surface, atmosphere, and interior. One of the most exciting observations of the spacecraft's wide-angle camera system, known as the Mars Orbital Camera, is that the red planet has very repeatable weather patterns. Each day the camera operates, it collects images that are used to build up a daily global map. These maps provide a record of changing meteorological conditions on Mars. Weather patterns observed by the spacecraft include some dust storms that repeat in the same location within a week or two of the time they occurred in the previous year. In addition, local disturbances and dust devils may start up at any time after the first day of spring and continue until Martian autumn.
A panoply of high-resolution images from the Mars Global Surveyor has documented gullies and debris flows suggesting that occasional sources of liquid water, similar to an aquifer, were once present at or near the surface of the planet. Magnetometer readings have shown that the planet does not have a global magnetic field but has localized magnetic fields in particular areas of the crust. Temperature data and closeup images of the Martian moon Phobos have determined that the moon is covered by a layer of powdery material -- the pulverized output of millions of years of meteoroid impacts -- at least 1 meter (3 feet) thick.
By studying Mars for several Martian years (a Mars year is about twice as long as an Earth year), Mars Global Surveyor has has observed gully formation, new boulder tracks, recently formed impact craters, and diminishing amounts of carbon dioxide ice within the south polar cap. Data from the spacecraft's laser altimeter has given scientists their first 3-D views of Mars' north polar ice cap. Changes in radio transmissions as they are refracted by the Martian atmosphere have enabled scientists to create vertical profiles of atmospheric temperature and pressure. Spacecraft accelerations due to gravity have given scientists a better understanding of the interior of Mars. Findings such as these have shown that Mars is a dynamic planet with a history of seasonal and long-term change recorded in the planet's surface.
During 2006, weather observations by the Mars Orbital Camera will be used to provide guidance for the aerobraking maneuvers of the Mars Reconnaissance Orbiter as well as daily assessments for the operation of the twin Mars Exploration Rovers. Detailed images will show if dust storms are present and whether the dust they kick up changes the density of the atmosphere through which the orbiter passes. This information is vital to operating the spacecraft as it uses atmospheric friction to slow down and trim its orbit. High-resolution images will also be used to select and confirm landing sites for the Phoenix and Mars Science Laboratory missions, scheduled for launch in 2007 and 2009, respectively.