Scientists working with NASA’s orbiting Mars Global Surveyor mission released photographs from several Martian locations that possibly indicated water had surfaced and flowed downhill, producing erosional features similar to those on Earth. After the initial press release, other photographs of geologically recent erosion were provided. These pictures reinforced the possibility of aquifers—water-giving, underground layers of earth—which would be vital for sustainable human colonization on Mars.
In anticipation of an article to be published in the June 30, 2000, issue of Science, imaging scientists announced the discovery of steep Martian slopes possibly disturbed by recently flowing water. The conclusion was based on photographs taken by an onboard camera of the Mars Global Surveyor (MGS). The pictures depicted erosion comparable to groundwater discharges and surface water drainage on Earth.
In 2002, a collaborative group of American and Australian geologists suggested the erosion was a consequence of liquid carbon dioxide. The group’s findings were based on laser altimetric data from the MGS. Publishing their speculations in Geophysical Research Letters, the geologists theorized that Martian temperatures, barometric pressures, and nonaqueous chemistry allowed for the temporary formation of liquid carbon dioxide. Consequently, the erosional influence of carbon dioxide on the formations photographed by the MGS could not be eliminated.
In November, 1996, the MGS was launched from Cape Canaveral in Florida aboard a Delta II rocket. Malin Space Science Systems (MSSS), of San Diego, California, designed, constructed, and operated the camera under contract to Jet Propulsion Laboratory
The science payload located on the nadir panel of the spacecraft. The Mars Orbiter Camera, at the top center, was designed to provide low-resolution images every day and high-resolution images of regions of scientific interest.
From late 1997 to March 1999, aerobraking—deceleration caused by passing through a planet’s atmosphere—lowered the spacecraft’s average two-hour orbit to a nearly perfect circle 450 kilometers (280 miles) above the planet’s surface at a 93-degree inclination in relation to the Martian poles. The vehicle’s polar orbit was oriented to the Sun at 1400 hours. Consequently, the orbital path was solar-synchronous with all mapped surface features that had the same latitudinal sun angles. The solar-synchronous orbit—when a vehicle or satellite is in continual sunlight—was used for the purposes of photographic illumination and contrast. Successfully positioned, the MSSS camera began its photographic survey as Mars rotated beneath the MGS.
The Martian surfaces that depicted recent hydraulic erosion were limited. Eroded hollows were imaged on steep, shaded slopes protected from direct sunlight at temperate and polar latitudes. Project scientists theorized that masses of surface ice eventually accumulated enough latent heat or impounded liquid mass to cascade gravitationally down steep slopes; through erosion, the Earth-like arroyos photographed by the MGS were produced. Upon reaching the bottom of the slopes, water quickly dissipated, possibly sublimating within the deeply shaded crevices, continuing the cycle of hydraulic erosion. None of the arroyos was found to have running water or carbon dioxide flowing downward.
The onboard spectrometer analyzed the chemical components of rocks, soil, ice, aerosols, and clouds. Laser altimeter data from the MGS found that Mars was, for the most part, very flat. Researchers interpreted this flatness as evidence of ancient basins once possibly filled with water. A photograph of an enormously broad lowland basin in the northern hemisphere exhibited the possible existence of ancient shorelines.
Previously, the Martian atmosphere was found to have only one-hundredth the mass of the Earth’s and to contain mostly carbon dioxide, with subordinate amounts of oxygen and nitrogen. Mars had no surface water and lacked the thermal protection of a true greenhouse effect, a benevolent process not possible without an abundance of water and atmospheric water vapor. Consequently, global surface temperatures were usually much colder on Mars than on Earth. Many scientists believed the greenhouse effect was the radiative consequence of atmospheric carbon dioxide. Paradoxically, the mass of Martian atmospheric carbon dioxide was one hundred times greater than its proportionate partial pressure on Earth, despite intensely colder Martian temperatures. Thus the critical difference between Mars and Earth was water and water vapor, not carbon dioxide.
The MGS spectrometers revealed the presence of hematite—the mineral form of iron oxide—on Mars. This was significant because hematite is sometimes the mineralogical consequence of an aqueous environment. It also pointed to the possible presence of bacteria-like organisms because bacteria can precipitate ferric oxides—or rust—from water, ferrous iron, and oxygen. At the time of NASA’s Mars Exploration Rover robotic missions, these processes and organisms were apparently absent or evasively cryptic.
A photograph of Mars showing a thin coating of water ice on the rocks and soil.
It remained for future generations to uncover the different fates that carbon dioxide and water had on Mars and on Earth. While the Earth accumulates water at its surface, Mars loses water at its surface. Evidence suggested Mars was severely dehydrated. The photographic depictions of water erosion produced by the MGS indicated the desert planet was still significantly dehydrating through processes yet to be completely and accurately described. Scientists hoped that additional information produced by the onboard spectrometers of the MGS, or information gathered by other international missions, would reveal the possible presence, and thus the location and depth, of subterranean water or carbon dioxide on the frigid, arid planet.
The MGS was scheduled to perform its tasks for one Martian year, approximately two Earth years. The MGS’s primary mission was completed in 2001, but its budget was extended three times to allow the onboard instruments and monitoring scientists to gather additional data. On November 2, 2006, radio contact was lost with the MGS. After repeated attempts to regain operational control of the MGS, it was declared lost in 2007. A wealth of information remained to be analyzed after the project’s termination, however. The value of this information was greatly enhanced when studied in conjunction with other Mars reconnaissance programs. Design, construction, deployment, and mission support cost American taxpayers approximately $400 million.
Photographs acquired by the MGS were made available to the general public via electronic resources administered by supporting agencies funded by American tax dollars. JPL was required to make the information gathered from its various Martian missions available for public dissemination and education. Any person wired to the resources of the World Wide Web could access Martian photographs and examine the circumstantial, topographical evidence for water or liquid carbon dioxide on the surface of Mars. At the beginning of the new millennium the citizens of Earth arguably had access to more data about the solid surfaces of Mars than about those of their own planet.
Scientific interest in the “Red Planet” had long centered on the prospects of water and life. Like the MGS, previous missions had circumstantially determined the ancient presence of water on Mars. Terrestrial organisms require water. Martian groundwater would enable the successful colonization of Mars via the drilling of wells for multiple uses by exploratory colonists. Water could be split—releasing hydrogen and oxygen—thus providing a breathable atmosphere. Like Earth, Mars also receives a steady stream of solar energy that could reliably produce electricity for future colonists.
Undoubtedly, the MGS mission significantly increased the circumstantial evidence for subterranean Martian water or carbon dioxide. Coupled with additional water-prospecting analyses, NASA and other space agencies could significantly move forward with collaborative planning, design, and construction of future Mars missions. Launched in 2003, NASA’s Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) began probing the Martian subsurface in 2005. Information from this and other missions is vital for the planning of future colonization.
For biological and geological purposes, direct investigations of Mars are superior to indirect examinations. Subsurface water would significantly improve the feasibility and sustainability of future science missions. Geologists and biologists, then, could directly examine Martian terrains for physical, chemical, and biological processes. From those observations, future scientists would be able to compare the evolution of Earth and Mars, two remarkably similar, but also very different, worlds.
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Head, James, et al. “Possible Ancient Oceans on Mars: Evidence from Mars Orbiter Laser Altimeter Data.” Science 286 (December 10, 1999): 2134-2137. A summary of high-resolution altimetric data from the northern Martian lowlands possibly indicating an ancient, water-filled basin. -
Malin, Michael, and Kenneth S. Edgett. “Evidence for Recent Groundwater Seepage and Surface Runoff on Mars.” Science 288 (June 30, 2000): 2330-2335. This article prompted the news conference and announcement of possible subsurface water on Mars and its potential uses for future colonization and scientific missions. -
Smith, D. E., et al. “Topography of the Northern Hemisphere of Mars from the Mars Orbiter Laser Altimeter.” Science 279 (March 13, 1998): 1686-1692. A preliminary analysis of topographical relief from altimetric data produced by the MGS, as prepared by participating project scientists from various institutions. -
Tanaka, K. L., et al. “Catastrophic Erosion of Hellas Basin Rim on Mars Induced by Magmatic Intrusion in Volatile-Rich Rocks.” Geophysical Research Letters 29, no. 8 (2002): 37.1-37.4. Presents an alternative, carbon dioxide-influenced explanation for Martian erosional formations.
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