Athena Review 2,2: Then and Now: On the Surface of Mars

Athena Review Vol.2, no.2

Then and Now: On the surface of Mars

Early Views of Mars: While Mars had been identified as a planet (wandering body) by the ancient Greeks, the 17th century Dutch astronomer Christiaan Huygens was the first to study Mars through a telescope. In 1659 he identified white spots at the poles of the otherwise orange-red globe, which he correctly identified as polar ice caps. These are now an intensive focus of study by NASA.

[Fig.1: Mars with north pole from the Hubble space telescope in 1997 (NASA/JPL/Caltech).]

The Italian astronomer Giovanni Schiaparelli, working with much larger and better telescopes between 1877 and 1890, saw blue-green patches on the surface of Mars. These he (incorrectly) thought to be seas which seemed to grow and shrink with the seasons, as if filled by the melting of polar ice. He also noted faint lines across the surface which he called canali, or channels, perhaps of natural origin.

The American Percival Lowell soon began to refer to the canali not as channels but as canals, possibly man-made. Lowell commenced serious study of Mars in 1894 through an 18 inch telescope near Flagstaff Arizona (now Lowell Observatory). He reasoned that the blue-green regions observed by Schiaparelli could not be seas because the canals, which themselves appeared to wax and wane with the seasons, in many cases flowed straight across the “seas.” As viewed from the Earth, however, these canals would be implausibly wide. He therefore proposed that the canals were actually belts of vegetation growing along waterways, much as trees grow along rivers on Earth. This interpretation spurred the belief that Mars was a dying planet and the canals were a last attempt by its inhabitants to concentrate their remaining resources, a scenario like many a science fiction story including War of the Worlds by H.G. Wells (1895).

Fig.2 Mars from the Global Surveyor, 1997. The dark area at right center is Syrtis Major, with clouds to the south (NASA/JPL/Caltech; Malin Scientific Systems).]

Lowell published Mars and its Canals in 1906, promoting his view that the canals of Mars were constructed by some highly advanced civilization. Lowell’s work received criticism from scientists such as Alfred Russel Wallace, codeveloper of the theory of natural selection. Ultimately, however (as noted by Carl Sagan, premier chronicler of Mars exploration), Lowell inspired many of his day. Besides Wells, the writer Edgar Rice Burroughs (also the creator of Tarzan) helped popularize the idea of life on Mars with a series of adventure books on the travels of Virginia gentleman John Carter, among Martians who resembled barbarian warriors and beautiful princesses.

Mars in the Space Program: Reality began to creep in after early spectroscopic scans of Mars in the 1940s and 50s showed its atmospheric pressure to be perhaps one-tenth that of the Earth, barely sufficient for liquid water. In July 1965 (after one US and six USSR failed missions), Mariner 4 made the first successful flyby of Mars, returning 22 photographs showing cratered plains like the Moon, but no evidence of the canals. It scanned a CO2 atmosphere with 5-10 mbar pressure, too low to support liquid water. In 1969 Mariners 6 and 7 confirmed the low atmospheric pressure of Mars, took over 200 pictures each, and showed virtually no water in ice caps seen as mainly frozen carbon dioxide.

In December 1971, the Soviet Mars 3 mission made the first successful soft landing on Mars, a week after Mars 2 had crashed. While the Mars 3 lander relayed only 20 seconds of video data before contact was lost, both orbiters returned atmospheric and temperature data through 1972.

[Fig.3: The giant Martian volcano Olympus Mons, 15 miles high (NASA/JPL/Caltech; Malin Scientific Systems).]

Meanwhile, US Mariner 9 reached Mars orbit Nov. 1971 during a huge duststorm. When the air cleared, its cameras revealed a much more complex planetary history. A huge volcanic range with giant caldera lay in the Tharsis region, with several of the largest known peaks in the solar system, including Mt. Olympus (fig.3), each dwarfing Mt. Everest. Such active interior geology could produce the molecules needed for life (including water). Importantly, Mariner 9’s images showed water had probably once flowed across the Martian surface in river-like channels. This provided a major research incentive for the Viking experiments and all later missions.

[Fig.4: Viking image of two large channels in the Xanthe Terra region; inset shows fig.5 (NASA/JPL/Caltech; Viking).]

The US Viking 1 and 2 missions, two lander-orbiter pairs designed to test for life on Mars, each landed successfully in 1976 (year of the US Bicentennial) amid ancient channels in Chryse and Utopia Planitia. The world watched as Viking 1 returned its first video stills of a cobble-strewn, arid red plain much resembling northern Arizona near the Lowell Observatory, or Death Valley. While Carl Sagan and colleagues joked about who would be the first to see a prospector on muleback, the robot Viking landers proceeded to take soil samples and performed three complex biochemical tests. These included a probe for organic molecules (with virtually none found), a radioactive, labeled release experiment (giving some ambiguous results), and a gas exchange experiment with anomalous findings later attributed not to life, but to highly oxidized clays on Mars. Until 1980 both orbiters documented the red planet’s surface with over 100,000 photos used to plan return trips by Pathfinder and Surveyor.

The 1993 loss of contact with NASA’s Mars Observer craft was forgotten by 1997 amid a very successful landing by the Mars Pathfinder mission, whose small, economical lander and tiny Sojourner rover jointly returned 16,550 images of rocky surface in Ares Valles, plus data from 15 chemical analyses of rocks, and wind and weather readings. The Global Surveyor orbiter, meanwhile, has returned detailed photos of Mars topography for two years, testing, confirming, or refuting theories that grew from Mariner and Viking imagery, from river channels and sedimentation (confirmed) to “the face of Mars” (not confirmed). Fig.5 shows a portion of the meandering canyons of the Nanedi Valles system, a valley about 2.5 km cutting across plains of the Xanthe Terra regionfirst imaged by Viking (fig.4). In the upper right corner is preserved a small, 200 m-wide channel (elsewhere, covered by dunes and debris) that indicates water must have flowed through this system for an extended period of time.

[Fig.5: Channels of Nanedi Valles system in the Xanthe Terra region, imaged recently by the Mars Global Surveyor (NASA/JPL/Caltech; MOC image 8704, Malin Space Systems).]

Mars Exploration, Present and Future: Many Earthlings feel nothing but awe for NASA’s skills of telemetry to land robots softly on the Moon and Mars, or to send craft a billion miles to precisely circle and image the icy moons of Neptune. It thus seems ironic that the Mars Climate Orbiter, after a perfect liftoff from Canaveral in 1998, should crash into Mars on Sept. 23, 1999 because somebody forgot to use the metric system in calculating final orbital insertion, and nobody at NASA/JPL bothered to check (thus voiding $125 million, and beefing up “Murphy’s Law”). The related Mars Polar lander, launched January 1999 to search for water near the South Pole (341 years after Huygens first identified it in a small telescope) was also lost during landing in December, 1999.

The 2000 Mars Odyssey Probe, however, achieved Mars orbit, and has now (Feb. 2003) returned important data showing recent water release due to melting snow in small channels at a crater's edge. Mars Exploration Rovers, scheduled for launch in May and June, 2003 will test such areas, as scientific interest in the geology and water environments of the red planet remain at a high level.

[For more information on NASA and JPL/Caltech, see http://www.jpl.nasa.gov ]

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