Mars Global Surveyor
New Gullies Form
on Sand Dune
Rolling Stones Make
New Boulder Tracks
4 Mars Years of
S Polar Changes
over Arsia Mons
High-Res Views of
cPROTO Mosaic in
Mars Global Surveyor (MGS) has been orbiting the red planet for 8 Earth years. For this month's anniversary of MGS's Mars Orbit Insertion, we take a moment to reflect upon the journey and describe the incredible value and scientific results of the Mars Orbiter Camera (MOC) during the MGS Extended Mission, which began after the Primary Mission ended in early 2001.
Twenty years ago this summer, in 1985, Mars scientists were busy writing proposals to NASA for science investigations to be conducted on the Mars Observer spacecraft. Selections were announced in 1986. The Mars Observer Camera (MOC) was among those instruments. Mars Observer launched in September 1992, and failed just days before reaching Mars in August 1993. Several of the Mars Observer science instruments were re-built for the Mars Global Surveyor (MGS) mission (the remainder were flown on Mars Climate Orbiter, Mars Odyssey, and the Mars Reconnaissance Orbiter).
MGS, carrying the new Mars Orbiter Camera (MOC), was launched from Florida in November 1996. It reached Mars and entered orbit around the planet 8 years ago, on 12 September 1997. After a period of aerobraking and initial, contingency science operations, MGS began its Primary Mission to observe the red planet for 1 martian year (687 Earth days) in March 1999. The Primary Mission ended on 31 January 2001.
Following the Primary Mission, the spacecraft entered an Extended Mission phase. Whether a planetary spacecraft's mission is extended is a function of two things: (1) the health of the spacecraft and its science instruments, and (2) the ability of the sponsoring agency (in this case, NASA), to continue to fund the spacecraft's operation. Mars Global Surveyor has had its mission extended three times, thus far, permitting MGS MOC to observe how the planet has changed over the course of more than 4 whole martian years.
Some of the most important discoveries about Mars that MGS has made would not have been possible without an Extended Mission. Much that is presently known about Mars would not be known. The most important discovery, in our opinion, is the recognition of a fossilized river delta in a crater that has been provisionally named 'Eberswalde' by the International Astronomical Union. This delta, featured in one of today's releases, provided the "smoking gun" evidence for persistent flow of water across the surface of Mars and deposition of water-lain sediment in a body of standing water. The sediment later became cemented to form sedimentary rock. This discovery preceded the revolutionary views of martian sedimentary rock provided by the Mars Exploration Rover, Opportunity, on Meridiani Planum.
The second most important discovery of the MGS MOC Extended Mission centered on the observation of changes in the south polar residual cap. This was initially noticed during the first year of the MGS Extended Mission, when we began to repeat earlier MOC images of the south polar "swiss cheese"-like terrain, with a goal of using the image pairs for stereo (3-d) and topographic mapping. What was found, instead, was that the scarps formed in the polar ice cap were retreating at a rate of about 3 meters (~10 ft) per Mars year. This is a phenomenal rate of geomorphic change, for any planet, and could only occur on Mars if the material is made largely of carbon dioxide, rather than water ice. MOC has now observed changes on the south polar cap that span four martian years; one of today's releases shows a "movie" documenting changes that were observed from 1999 to 2001 to 2003 to 2005. Each year, the scarps retreated about 3 more meters; MOC has seen no evidence for new carbon dioxide deposition. This suggests that the climate is presently warmer (and perhaps still getting warmer) than it was several decades to centuries ago, when the carbon dioxide was originally deposited. In other words, Mars, like Earth's Ice Ages, has had recent periods in which the climate was colder than it is today.
During the MGS MOC Extended Mission, the camera and spacecraft operations teams worked very closely together to implement and then use on a routine basis two techniques that have improved our opportunities to target features of high scientific interest, and to sometimes image them at spatial resolutions higher than 1 meter (~3 ft) per pixel.
The first technique, called ROTO (Roll Only Targeted Observation), was developed in 1998 to image the Viking, Mars Pathfinder, and "Face on Mars" sites, and further developed in 1999/2000 to search for the lost Mars Polar Lander. With the start of the Extended Mission in February 2001, the MOC operations team began routinely targeting ROTO images, with sometimes as many as 10-16 targets per week. This vastly increased the science team's ability to repeatedly monitor areas of high scientific interest, complete mosaics (e.g., of the Eberswalde delta), and acquire critical data to assess landing sites for the Mars Exploration Rovers and the 2007 Phoenix lander.
The second technique, called cPROTO (Compensated Pitch and ROll Targeted Observation), permits MOC to obtain images with approximately 50 centimeters/pixel of down track spatial resolution, 150 centimeters/pixel of cross track resolution. Initially developed in 2003, this method became routinely employed in 2004 and 2005 to obtain very high spatial resolution images of key science targets (gullies, sedimentary rocks, polar landforms) and landing sites (MER, Phoenix, Viking, Mars Pathfinder). Indeed, without the cPROTO technique, the location of the Viking 2 lander and its geologic context would remain unknown to this day.
All the while, the MOC Wide Angle red and blue cameras continued their daily global monitoring of the red planet. Systematic global observations began in March/April 1999. MOC has now observed the weather on Mars nearly every day for a period spanning four Mars years. The wide angle cameras have shown us that Mars has fairly predictable weather, with some storms and cloud phenomena repeating every year, like clockwork. There are specific times of year and locations on Mars which have experienced the same dust storm patterns every Mars year since we began observing with the first MGS MOC approach image in July 1997. The release presented here gives another example -- the annual repeated spiral clouds that form over Arsia Mons at the beginning of southern spring.
Still other weather events do not seem to be as repeatable -- for example, in 2001 Mars had a global dust storm event. MOC images have shown that Mars has a global dust event every year, but in some years the storm activity is more intense, with very large regional dust storms that kick dust high into the atmosphere. More importantly, MOC images of the 2001 event showed that there really is no such thing as a "global dust storm," in which the entire planet is embroiled in windy conditions and vigorous raising of dust clouds. Unlike what is commonly depicted in science fiction films and novels, much of the planet is actually quite calm during global dust events. It is the dust lofted high into the atmosphere by a few large, regional storms that leads to the global obscuration of the surface that has come to be called a "global dust storm."
An additional, key benefit of MOC's Extended Mission activities has been to support the Mars Exploration Rover (MER) project. MOC images were used to help select and certify the MER landing sites. As the twin spacecraft approached the planet, MOC wide angle images were used to monitor weather conditions at the two landing sites. This weather monitoring has continued throughout the MER Primary and Extended Missions. Finally, the MOC computer buffer is the only buffer onboard MGS that is large enough to record data relayed to MGS from landers and rovers on the martian surface. The MGS/MOC data relay system provided critical support during each MER's Entry, Descent, and Landing in January 2004, and MGS/MOC continued to relay data from the two rovers through mid-2004. Today, MGS/MOC stands ready as a back-up system to the Mars Odyssey relay, to ensure return of MER data in the event that Odyssey cannot do so.
The MGS Extended Mission is currently funded through 2006. This will ensure continuity of the daily global weather coverage from Mars Global Surveyor's MOC to the Mars Reconnaissance Orbiter (MRO) Mars Color Imager (MARCI). MGS's observations of martian weather will also be used to help the MRO mission operations team conduct MRO's critical aerobraking maneuvers in 2006. Extending MGS's mission beyond 2006 is, of course, highly desirable for improving our understanding of Mars. With MRO in a 3 p.m. orbit, and MGS in a 2 p.m. orbit, coordinated daily global observations with the MOC wide angle cameras and the MRO MARCI will permit Mars meteorologists to track and measure the wind speeds of dust storms and clouds as they move over the span of the 1 hour between the MGS and MRO observations.
A further extension for MGS will also permit MOC to continue to acquire the thousands of images needed to monitor the changes that take place on the planet -- south polar scarp retreat, slope streaks, dust devils and dust devil tracks, rockfalls, and occasional new impact craters. More importantly, MOC will be able to continue its on-going campaigns to look for evidence of sand dune movement and gully formation. In 2000, we reported that slopes at middle and high latitudes on Mars exhibit an abundance of geologically young gullies. Were these gullies formed by recent seepage of ground water? At the time, it seemed entirely possible that some gullies might be active today. MOC has been monitoring gullies seen earlier during the MGS mission, as well as discovering new gullies, in an attempt to determine whether any of them are presently active. We're looking for new gullies, evidence of change in a gully, and -- perhaps more telling and exciting -- evidence that unseasonable ice has formed on the floor of a gully channel. Such ice would be terrific evidence of a recent flow. MOC will be able to devote resources not available to the MRO instruments in order to continue these monitoring and tracking efforts. As the MOC narrow angle camera system has only imaged under 5% of the martian surface, it remains possible that the most important MOC discoveries are yet to come.