Educational Product National Aeronautics and Educators I Grades 512 Space Administration EB-1999-02-128-HQ Educational Brief Exploring Mars HY EXPLOREMARS? Why would we explore Mars, the fourthplanet fromthe Sun, the next outward Wfromthe Earth? What is there forhumankind? Through a telescope, Mars' red light reveals few details, an orange round world splashed with gray; white poles; rarely obscured by clouds. Close up, Mars is stunning: clouds hovering above lava-draped volcanos; nearly endless chasms, their depths lost in mist; towering ice cliffsstriped with red. Mars' past is laid bare in the landscape. Impact scars mark world-jarring collisions with asteroids, and deep winding channels recall titanic floods. But robot eyes alone have seen these sights, and then only from orbit high above. Mars is the only planet besides Earth that was ever cut by flowingwater or graced by lakes and ponds. Now, that water is frozenat the poles and buried beneath Mars' frigiddeserts. In those ancient martian pools, might life have sprung up and prospered? The pools are dry and sterile today, but could life persist in deep and hidden places? Someday, will humans walk those distant deserts, seeking signs of ancient life? Mars seen fromEarth orbit. A HISTORY OF EXPLORATION umans have known of in an ellipse, not a circle. Seventy-fiveyears later, Kepler's H Mars since beforere­ solution was crucialto Isaac Newton's discovery of the law of corded history. Even 3600 years gravity. ago, the Babylonians wrote about Mars' While Kepler explained its orbit, Galileo Galilei transformed looping motion across the Mars into a world. In 1609, Galileo firstviewed Mars through his sky and changing brightness. newly invented telescope. Although his telescope was no better Mars was one of five "stars that than a modem toy, it revealed enough to prove that Mars was a wandered" among the fixedstars large sphere, a world like the Earth. Could this new world be of the night, and was special Thecaldera at thesummit inhabited? As telescopes improved, more of Mars could be seen: because of its color: red. In of theOlympus Monsvol­ polar icecaps, color patterns on its face,clouds, and hazes. These ancient India, Mars appeared like cano is 90 kilometers observations all fita habitable planet, and speculations that Mars a fire in the sky - formany other across and about 2 kilo- was inhabited became more and more believable. cultures, its redness recalled the meters deep. The idea of living martians came to fullflower in 1877 when fire and blood of war. In ancient the Italian astronomer Giovanni Schiaparelli observed thin dark Greece, the red wanderer personifiedthe god of war, "Ares." lines crossing Mars' bright "continents." He called the lines When the Romans conquered Greece, they adopted this symbol­ "canali," "channels" in Italian, and the word was widely misread ism and named the planet fortheir god of war, "Mars." as "canals." In the U.S., Percival Lowell seized on the canals as Through the Middle Ages, astrologers studied Mars' motions proof of a martian civilization, advanced enough to move water to help them predict the future- if Mars moved unfavorably, across a whole world. Many scientists agreed, but most thought wars would be lost! But no one could predict Mars' motion that the canals were optical illusions.They thought that Mars was accurately, even using Copernicus' theory (of 1543) that the too cold and its air too thin forlife as we know it. planets orbit incircles around the Sun. Johannes Kepler solved Understanding of Mars advanced little from Lowell's time in this puzzle in 1609 when he discovered that Mars orbits the Sun the late nineteenth century until 1965, when the Mariner4 1 spacecraftflew within 10,000 kilometers of the martian surface. Its pictures, the first close-up views of Mars, showed a Moonlike landscape of plains pocked by impact craters. There were no canals or other signs of life. Mariner 4 finally proved that Mars' atmosphere, only 0.7% as thick as the Earth's, was much too thin for life as we know it. Four years later the twin spacecraftMariner 6 and Mariner7 flewby Mars again, carrying cameras and spectrometers to measure the temperature of Mars' surface and the composition of its atmosphere. Their photos again showed no canals or other signs of life, but did reveal a volcano, plains without impact craters, and areas of chaotic hills. Mars' mass and density were calculated from spacecraft tracking. Thespectrometers showed that Mars was very cold (-123°C at the south pole), and that Mars' thin atmosphere was almost all carbon dioxide. At the time, Apollo11 's landing on the Moon overshadowed the successes of Mariners 6 and 7. Exciting as they were, the early Marinersonly spent a short These channels in Maja Valles were cut by giant floods at some time near Mars as they flewpast; more time was needed, and that point in the history of Mars. The scene is 225 kilometersacross. meant going into orbit. So in 1971, Mariner9 arrived at Mars and became the first artificialobject ever to orbit another planet. Angeles to New York! Giant valleys extend fromthe Valles and More than twice as big as its predecessors, Mariner 9 carried elsewhere and are mute testimony to devastating floodsin Mars' color cameras and new instruments tailored to investigating Mars' distant past. Most of the valleys end in the northernplains, a vast surface and atmosphere. An unsung part of the spacecraftwas its lowland encompassing almost a third of the planet. There,the computer system, which allowed Mariner 9 to wait until Mars' floodwatersponded into huge lakes or perhaps even an ocean. atmosphere cleared of a planetwide dust storm. Mariner 9 Signs of water appear in the southernhighlands too, forthe most operated for almost a year, mapped 85% of Mars' surface in more part as small valleys draining away fromthe largest craters and than 7000 images, analyzed Mars' gravity field,measured surface uplands. Despite these signs of ancient water, Mars now is too temperatures and dust abundances, and measured temperatures cold and its atmosphere too thin forliquid water to remain. and humidity of its atmosphere. Mariner 9 also was the firstto see Mars' volcanos, the Mariner 9's view of Mars was the firstdetailed global view biggest in the solar system. The biggest of all, Olympus Mons, is of another planet; it revealed a "New Mars," unlike any earlier 600 kilometers across at its base and 25 kilometers tall. Smaller concept. The earlier Mariners saw land typical of the southern volcanos and lava flows appear all over Mars, especially on the hemisphere: craters and more craters. Mariner 9 saw what they Tharsis Rise, a huge bulge distorting Mars' spherical shape. missed such as the Valles Marineris, a canyon up to 100 kilome­ Looking toward space, Mariner 9 took the firstclose-up images ters wide and 10 kilometers deep that would reach fromLos of Mars' moons, Phobos and Deimos. They are little more than large potato-shaped rocks, about 10 kilometers long, and appear similar to asteroids. Mariner 9's global perspective and spectacular images of water-carved landscapes inspired further exploration of Mars to focuson the search forlife. Afterextensive development, the twin spacecraft Viking1 and 2 were launched in 1975 and entered Mars orbit in 1976. Each Viking was actually two spacecraft: an orbiter and a lander. Each orbiter had a pair of cameras and instruments formapping surface temperature and atmosphere humidity. Each lander included a weather station, a seismometer fordetecting "marsquakes," instruments for analyzing soil, and a stereo TV camera. The Vzking1 lander touched down gently on July 20, 1976, on Chryse Planitia in the northernlowlands. Its robot eyes took the first photos of the martian surface: a rolling desolation of dark rounded rocks and brick-red dust under a pinksky. The rocks are probably volcanic, pitted and smoothed by eons of blowing sands. On landing, the winds were light, at most 30 kilometers per hour. Vzking1 sits at a latitude comparable to the Sahara Desert on Earth, but its daytime temperatures climbed to a Ceraunius Tholus volcano on theTharsis Rise. Thescene is 215 km high of -10°C (14 °F), and dropped to a numbing -90°C (-130°F) across. before sunrise. 2 atmosphere is now colder and much less dusty than during the Viking missions. Clouds of water ice are more abundant now than during the Viking missions, and show how water moves frompole to pole as Mars' seasons change. Another highlight in Mars exploration was the discovery that a fewmeteorites on Earth came originally fromMars! These meteorites contain traces of gas identical to the martian atmo­ sphere as analyzed by the Vikinglanders. Asteroid impacts ejected the meteorites offMars into orbit around the Sun; after millions of years, they landed on the Earth. The martian meteor­ ites are all volcanic rocks, most are young (erupted only 180 million years ago), and almost all have reacted with martian groundwater. These meteorites have revolutionized thinkingabout Mars' atmosphere and its water, and are "ground truth" for Darkrocks and whitefrost at the Viking 2 lander site. The largest interpreting images of the distant geology of Mars. The martian rocks areabout 1 meter long. meteorites are almost like sample returnmissions, except we don't know where on Mars they formed. Some scientists believe that one martian meteorite includes traces of ancient martian The Viking2 lander touched down two months later on life - fossilizedmartian bacteria. However, many scientists Utopia Planitia, closer to Mars' north pole, a latitude comparable remain unconvinced by this claim, which is now a topic of intense to Maineor Mongolia on Earth. The plains of Utopia are rockier investigation. than the Viking 1 site in Chryse; one of Viking2's legs stands on a rock.