Chapter 5 Scientific Exploration of Mars UNDERSTANDING MARS successfully inserted Mariner 9 into an orbit about Mars8 on November 13, 1971. It was the The planets have fascinated humankind ever first spacecraft to orbit another planet (box 5-A). since observers first recognized that they had For the first 2 months of the spacecraft’s stay in characteristic motions different from the stars. Mars’ orbit, the most severe Martian dust storms Astronomers in the ancient Mediterranean called ever recorded obscured Mars surface features. them the wanderers because they appear to wan- After the storms subsided and the atmosphere der among the background of the stars. Because cleared up, Mariner 9 was able to map the entire of its reddish color as seen by the naked eye, Mars Martian surface with a surface resolution of 1 9 drew attention. It has been the subject of scientif- kilometer. ic and fictiona13 interest for centuries.4 In recent Images from Mariner 9 revealed surface fea- years, planetary scientists have developed in- tures far beyond what investigators had expected creased interest in Mars, because Mars is the from the earlier flybys. The earlier spacecraft had most Earthlike of the planets. “The study of Mars by chance photographed the heavily cratered is [therefore] an essential basis for our under- southern hemisphere of the planet, which looks standing of the evolution of the Earth and the more like the Moon than like Earth. These first inner solar system.”5 closeup images of Mars gave scientists the false Planetary exploration has been one of the Na- impression that Mars was a geologically “dead” tional Aeronautics and Space Administration’s planet, in which asteroid impacts provided the (NASA) primary goals ever since the U.S. civilian primary agent for altering its surface geology. space program was started in 1958.6 As the next Mariner 9 showed instead that Mars also had planet from the Sun beyond Earth, and the sub- huge volcanoes, complex fault zones, and an enor- ject of intense ground-based observations prior mous canyon some 2,800 miles long just south of to the first satellite launch, Mars has received the equator, named Vanes Marineris by the particular attention. After sending three Mariner NASA spacecraft team.10 Detailed examination spacecraft on Mars “flybys” in the 1960s,7 NASA of numerous channels and valleys suggests that l~e tem c~planet~t derives from the Greek word meaning to wander. ~bservations of Mars dominated the scientific interest of Percival Lowell, founder of Lowell Observatory. He popularized the incorrect notion that the surface of Mars was covered with canals, a claim first advanced by Giovanni Virginio Schiaparelli in 1877. JFor e=mple, the inteW]anetaV invade~ of H.G. Wells’ 1897 novel War o~lhe Worlds were suppo~d to have come from Mars. firlY in this centuty, Edgar Rice Burroughs wrote an entire series of adventure novels set on Mars. dsee John Noble Wilford, Man Bec~m (New York, NY: Knopf, 1990), for a highly readable historical summary of the interest in Mars by Western civilization. sNational Re~arch Council, Space Science Board Committee on Planetary and Lunar @loration, SZrategY for fiplorah”on of tie znner~/an- ets: 1977-1987 (Washington, DC: National Academy of Sciences, 1978), p.43. %I%e National Aeronautics and Space Act of 1958 was signed by President Dwight D. Eisenhower on July 29,1958, and became law on Oct. 1, 1958. TMannem 4, 6, and 7 successfully returned sufiace images and other data. Manner 3 failed before reaching the Planet. 8N~A planned t. ~nd ~. identical spacecraft t. Mare) in part to provide redundancy in ca~ one spacecraft failed. Placing the tWO SpaC& craft in different orbits would have allowed the two to provide a complete survey of the planet relatively quickly. However, the first spacecraft, Mariner 8, was lost when the Centaur stage on the Atlas-Centaur launch vehicle malfunctioned shortly after liftoff. %l%is implies that objects equal to or greater than about 1 kilometer diameter could be distinguished on the images. In practice, the ability to resolve surface features also depends on other factors, e.g., the viewing conditions, surface contrast, and processing capabilities. lo~ard Clinton well and Linda Neumann ~el], On Mare: Exploration of the Red Planet 1958-1978 (Washington, DC: National Aeronautics and Space Administration, 1984), pp. 288-297. -65- 66 ● Exploring the Moon and Mars Box 5-A – Findings of Mariner 9 Mariner 9 reached Mars in late 1971 and became the first spacecraft to orbit Mars. During the first several weeks of its orbital stay, Mariner 9 encountered a dust storm that completely obscured the surface. Over time, however, the spacecraft provided a complete record of the surface features on Mars at resolu- tions of 1 to 3 kilometers, which allowed NASA and the U.S. Geological Survey to compile a topographic map of the planet. About 2 percent of the surface in specific areas was imaged at 100- to 300-meters resolu- tion. Mariner 9 discovered massive volcanic mountains, deep channels that reveal evidence of fluid flow in the distant past, and layered sediments in the polar regions. Mariner 9 revealed a hemispherical global dichotomy (half the planet has craters dating from the early history of the planet, while the other half has few craters). observations of the cloud systems revealed westerly winds in winter and easterly winds in the sum- mer, weather fronts, lee wave clouds, ice fogs, and other atmospheric meteorological phenomena. Mari- ner 9 observations led to the realization that Mars has experienced both secular and periodic (cyclic) climate changes. An infrared interferometer spectrometer evaluated the extremely small amount of atmospheric wa- ter vapor, and demonstrated that it exhibits strong seasonal variations. The Mariner 9 ultraviolet spec- trometer showed that the amount of ozone in the atmosphere, which is found only in the polar regions, vanes with the seasons. It is greatest during the winter, when it reaches some 2 percent of the ozone in Earth’s atmosphere, and falls to zero in the Mars summer. The virtual lack of ozone allows ultraviolet light to reach the Martian surface and destroy any organic compounds present in the soil. SOURCE: W.K. Hartmann and O. Rasper, The Discoveries ofMariner 9, NASA SP337 (Washington, DC: U.S. Government Printing Office, 1974); Michael C. Malin, Arizona State University, 1991. flowing water was once common on Mars.ll Some The Viking program launched two spacecraft scientists speculate that before this water disap- toward Mars in 1975. 14 They were carried into peared from the surface, it may have made life orbit by two Titan III launch vehicles on August 12 possible. 20, 1975 and September 9, 1975, respectively. Af- The scientific arguments for finding evidence ter searching the surface with high-resolution of extinct or existing life on Mars had been noted cameras to select safe landing sites, the Viking 13 as early as 1959. However, only after the Mari- craft landed on the surface in 1976, photographed ner 9 images were available did scientists have the surroundings, analyzed the soil, and tested for direct evidence of the past existence of water that evidence of life (box 5-B). The test for life on Mars might have supported life. This finding lent addi- was inconclusive, although nearly all scientists tional support to those scientists interested in searching for evidence of extinct or present life on agree that it showed that no living organisms 15 Mars and spurred development of life-seeking existed at the Viking sites. These tests, however, instruments on the Mars Viking spacecraft that made the unexpected discovery that Martian soil were then in the design stages. in the vicinity of Viking landers is highly reactive llMichael H. Cam, “Mars: A Water-rich Planet,” lcarus, vol. 68, 1986, pp. 187-216; “Water on Mars,” Nature, vol. 326, 1987, Pp. 30-35. l~hristopher R McGy and Carol R. Stoker, “The E@ Environment and Its Evolution on Mars: Implications for Life,” Reviews o~Ge~PhY~- ics, vol. 27, No. 2, 1989, pp. 189214. lssee the Summaw histow of the early search for life on Mars in ~ell and fiell, op. cit., footnote lo) Ch. 3. Idorginally planned for launch in 1973, the Viking launches were slipped to 1975 as a result of a severe budget squeeze. l~is conclusion is based not only on the biology experiments but other experiments that attempted to detect organic material in the soil. The conclusion that life does not exist at the Viking sites cannot be extended to other sites on the planet where conditions more conducive to life, e.g., hydrothermal vents, might exist. Chapter 5–Scientific Exploration of Mars .67 Box 5-B – Findings From the Viking Mars Landers NASA sent two Viking spacecraft to Mars in 1975, which reached Mars orbit in 1976 after nearly a year in transit. Upon reaching Mars orbit, the orbiters surveyed the surface at high resolution to select the best landing sites for the Viking 1 and 2 landers. Both landers separated from their parent craft and ex- ecuted soft landings at different sites in July and September, 1976, respectively. Viking 1 landed at a site on Chryse Planitia at 22.3 North latitude, 48.0 degrees longitude. Viking 2 landed at the same longitude on Utopia Planitia 25.4 degrees North of Viking 1. The orbiters then began to relay visual images and other data from the landers back to Earth. Although both orbiters and landers were expected to complete their missions within a few months, they lasted far beyond their design lifetimes and continued to transmit data to Earth for several years.