Mars Global Surveyor

On 2 November 2006, NASA lost contact with the spacecraft after commanding it to adjust its solar panels. Several days passed before a faint signal was received indicating that the spacecraft had entered safe mode and was awaiting further instructions.[3]

On 21 and 22 November 2006, MGS failed to relay communications to the Opportunity rover on the surface of Mars. In response to this complication, Mars Exploration Program manager Fuk Li stated, "Realistically, we have run through the most likely possibilities for re-establishing communication, and we are facing the likelihood that the amazing flow of scientific observations from Mars Global Surveyor is over."[8]

On 13 April 2007, NASA announced the loss of the spacecraft was caused by a flaw in a parameter update to the spacecraft's system software.[3] The spacecraft was designed to hold two identical copies of the system software for redundancy and error checking. Subsequent updates to the software encountered a human error when two independent operators updated separate copies with differing parameters. This was followed by a corrective update that unknowingly included a memory fault which resulted in the loss of the spacecraft.

Originally, the spacecraft was intended to observe Mars for 1 Martian year (approximately 2 Earth years). However, based on the vast amount of valuable science data returned, NASA extended the mission three times. MGS remains in a stable near-polar circular orbit at about 450 km altitude, and was expected to crash onto the surface of the planet at some point after about 2047 at the time of its original launch, having by then spent fifty years orbiting the red planet. This is to prevent contamination of the Martian surface with any germs that may be stuck to the spacecraft.[4]

The Mars Orbiter Camera

TES

Five scientific instruments flew aboard MGS:[10]

• The Mars Orbiter Camera (MOC) operated by Malin Space Science Systems- The Mars Orbiter Camera (MOC), originally known as Mars Observer Camera,[11] used 3 instruments: a narrow angle camera that took (black-and-white) high resolution images (usually 1.5 to 12 m per pixel) and red and blue wide angle pictures for context (240 m per pixel) and daily global imaging (7.5 km per pixel). MOC returned more than 240,000 images spanning portions of 4.8 Martian years, from September 1997 and November 2006.[12]
• The Mars Orbiter Laser Altimeter (MOLA) - MOLA was designed to determine Mars' global topography. It operated as an altimeter until a portion of the laser reached end-of-life in June 2001. The instrument then functioned as a radiometer until October 2006.[13]
  

  High resolution topographic map of Mars based on the Mars Global Surveyor laser altimeter research led by Maria Zuber and David Smith. North is at the top. Notable features include the Tharsis volcanoes in the west (including Olympus Mons), Valles Marineris to the east of Tharsis, and Hellas basin in the southern hemisphere.
• The Thermal Emission Spectrometer (TES) - This instrument mapped the mineral composition of the surface by scanning thermal emissions.[13]
• A magnetometer and electron reflectometer (MAG/ER) - This instrument was used to interrogate the planet's magnetic fields and determine that Mars does not have a global magnetic field but rather many smaller localized fields.
• The Ultrastable Oscillator (USO/RS) - Precise clock measurements from this device were used to map variations in the gravitational field.[13]
• The Mars Relay (MR) - The Mars Relay antenna supported the Mars Exploration Rovers for data relay back to Earth in conjunction with the Mars Orbiter Camera's 12 MB memory buffer.[10]

The spacecraft circled Mars once every 117.65 minutes at an average altitude of 378 km (235 mi). The nearly polar orbit (inclination = 93°) which is almost perfectly circular, moved from the south pole to the north pole in just under an hour. The altitude was chosen to make the orbit Sun-synchronous, so that all images that were taken by the spacecraft of the same surface features on different dates were taken under identical lighting conditions. After each orbit, the spacecraft viewed the planet 28.62° to the west because Mars had rotated underneath it. In effect, it was always 14:00 for MGS as it moved from one time zone to the next exactly as fast as the Sun. After seven sols and 88 orbits, the spacecraft would approximately retrace its previous path, with an offset of 59 km to the east. This ensured eventual full coverage of the entire surface.[10]

In its extended mission, MGS did much more than study the planet directly beneath it. It commonly performed rolls and pitches to acquire images off its nadir track. The roll maneuvers, called ROTOs (Roll Only Targeting Opportunities), rolled the spacecraft left or right from its ground track to shoot images as much as 30° from nadir. It was possible for a pitch maneuver to be added to compensate for the relative motion between the spacecraft and the planet. This was called a CPROTO (Compensation Pitch Roll Targeting Opportunity), and allowed for some very high resolution imaging by the onboard MOC (Mars Orbiting Camera).[17]

In addition to this, MGS could shoot pictures of other orbiting bodies, such as other spacecraft and the moons of Mars. In 1998 it imaged what was later called the Phobos monolith, found in MOC Image 55103.[18]

The Phobos monolith (right of center) as taken by MGS (MOC Image 55103) in 1998.

After analyzing hundreds of high-resolution pictures of the Martian surface taken by the spacecraft, a team of researchers found that weathering and winds on the planet create landforms, especially sand dunes, remarkably similar to those in some deserts on Earth.[19]

Other discoveries from this mission are:

• The planet was found to have a layered crust to depths of 10 km or more. To produce the layers, large amounts of material had to be weathered, transported and deposited.

• 
  Layers in an old crater in Arabia, as seen by MGS, under the MOC Public Targeting Program. Layers may form from volcanoes, the wind, or by deposition under water. The craters on the left are pedestal craters.
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  Layers in crater found within the Schiaparelli crater basin as seen by MGS. Image from the Sinus Sabaeus quadrangle.
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  Buttes and layers in Aeolis quadrangle, as seen by MGS.

• The northern hemisphere is probably just as cratered as the southern hemisphere, but the craters are mostly buried.
• Many features, like impact craters, were buried, then recently exhumed.

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  Crater that was buried in another age and is now being exposed by erosion, as seen by the Mars Global Surveyor under the MOC Public Targeting Program. Image is located in the Noachis quadrangle.
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  Lava flows were once covered over, now these platy flows are being exposed.
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  Crater was buried, now it is being exhumed by erosion. Image located in Ismenius Lacus quadrangle.
• 
  The northern hemisphere appears smooth, but the craters are covered over. Here, a group of craters are partially exposed. Image located in Cebrenia quadrangle.

• Large areas of Mars are covered by a mantle that coats all but the very steepest slopes. The mantle is sometimes smooth, sometimes pitted. Some believe the pits are due to the escape of water through sublimation (ice changing directly to a vapor) of buried ice.

• 
  Close up image of Phaethontis surface taken by Mars Global Surveyor, under MOC Public Targeting Program. Pits are thought to be caused by buried ice turning into a gas.
• 
  The mantle drapes most of the area. Note the absence of boulders on the cliff face. An area that shows the edges of the mantle is circled. Image located in Ismenius Lacus quadrangle.
• 
  Mantle material, as seen by MGS.
• 
  Steep cliff in Ismenius Lacus quadrangle with smooth mantle covering its face. Picture taken under MOC Public Targeting Program.

• Some areas are covered by hematite-rich material. The hematite could have been put in place by liquid water in the past.[20]
• Dark streaks were found to be caused by giant dust devils. Dust devil tracks were observed to frequently change; some changed in just one month.[21]

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  Pattern of large and small tracks made by giant dust devils as seen by Mars Global Surveyor, under the MOC Public Targeting Program. Image is located in Eridania quadrangle.
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  Kepler (Martian crater) showing dust devil tracks, as seen by Mars Global Surveyor. Kepler is a large crater in the Eridania quadrangle.
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  Dust devil, as seen by MGS.
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  Dust devil in action showing shadow to the right. Image located in Cebrenia quadrangle.

• The south pole's residual cap was observed to look like Swiss cheese, with holes generally a few meters deep. The holes get bigger each year, so this region or hemisphere may be warming.[22] Claims that this represents a global trend, however, are cherry-picking regional data versus the planetary dataset, and MOC results versus TES and radio science (see below).

• 
  Changes in south pole from 1999 to 2001, as seen by Mars Global Surveyor. Notice how Swiss-cheese type holes have grown in the two years.
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  Swiss cheese terrain, as seen by MGS. Largest mesa in image is 4 meters high.
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  Layers in Swiss cheese terrain. There is a bright upper layer and a darker lower layer.
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  Close-up view of Swiss cheese terrain. Polygonal pattern was probably formed by shallow troughs.

• The Thermal Emission Spectrometer observes in infrared for atmospheric studies and mineralogy.[23][24][25] TES found that Mars' planetary climate has cooled since Viking,[26] and just about all of the surface of Mars is covered with volcanic rock.

• 
  Ceraunius Tholus, one of many volcanoes found on Mars.
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  Lava flows in the Tharsis quadrangle.
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  Image shows both young and old lava flows from the base of Olympus Mons. The flat plain is the younger flow. The older flow has channels with levees along their edges. The presence of levees is quite common in many lava flows.
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  Small volcano in Phoenicis Lacus quadrangle. Image covers a distance 1.9 mi (3.1 km) long.

• Hundreds of house-sized boulders were found in some areas. This indicates that some materials are strong enough to hold together, even when moving downslope. Most of the boulders appeared in volcanic regions so they were probably formed from weathered lava flows.[27]

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  House-sized boulders are scattered throughout this image.
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  These boulders are near Ascraeus Mons, a Martian volcano. Volcanoes on Mars probably form hard boulders made up of basalt that is resistant to erosion in the current environment of Mars.

• Thousands of dark slope streaks were observed. Most scientists believe they result from the avalanching of dust.[27] However, some researchers think that water may be involved.[28]

• 
  Many streaks underwent changes during the many years that MGS functioned.
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  Tikonravev Crater floor, as seen by Mars Global Surveyor. Click on image to see dark slope streaks and layers. Tikonravev Crater is in the Arabia quadrangle.
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  Dark streaks in Diacria quadrangle, as seen by Mars Global Surveyor, under the MOC Public Targeting Program.

Data from MGS have been used to perform a test of the general relativistic Lense–Thirring precession which consists of a small precession of the orbital plane of a test particle moving around a central, rotating mass such as a planet. The interpretation of these results has been debated.[29][30]

Hundreds of gullies were discovered that were formed from liquid water, possibly in recent times.[31][32][33]

• 
  Group of gullies on north wall of crater that lies west of the crater Newton (41.3047 degrees south latitude, 192.89 east longitude). Image taken by Mars Global Surveyor, MOC Public Targeting Program. Image is located in the Phaethontis quadrangle.
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  Gullies in a crater in Eridania quadrangle, north of the large crater Kepler. Also, features that may be remains of old glaciers are present. One, to the right, has the shape of a tongue. Picture taken under the MOC Public Targeting Program.
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  Gullies on one wall of Kaiser Crater. Gullies usually are found in only one wall of a crater.
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  Full color image of gullies on wall of Gorgonum Chaos. Image is located in the Phaethontis quadrangle.

A few channels on Mars displayed inner channels that suggest sustained fluid flows. The most well-known is the one in Nanedi Valles. Another was found in Nirgal Vallis.[27]

Inner channel on floor of Nanedi Valles that suggests that water flowed for a fairly long period. Image from Lunae Palus quadrangle.

On 6 December 2006 NASA released photos of two craters in Terra Sirenum and Centauri Montes which appear to show the presence of flowing water on Mars at some point between 1999 and 2001. The pictures were produced by Mars Global Surveyor and are quite possibly the spacecraft's final contribution to our knowledge of Mars and the question of whether water exists on the planet.[34]

Evidence of possible recent water flow