MARS (MYTHOLOGY) In Roman mythology, Mars was the god of war, of agriculture, and of the state. He was the parthenogenetic son of Juno, the husband of the goddess Bellona, and the lover of Venus. He was originally Mars Sylvanus, a god of spring vegetation. As Mars Gradivus, he was identified with the Greek war god ARES. His festivals in March (the month was named for him) and October marked the opening and closing of the military campaign season. As Mars Quirinius, god of the state, he was the father of ROMULUS AND REMUS by the vestal virgin Rhea Silvia. He saved them from drowning in the Tiber and raised them with the help of the she-wolf and the sacred woodpecker Picus. The wolf, the woodpecker, the horse, and the color red were associated with him.
Mars Bleeding warrior/Fallen god the last word from the Mariner was of your death Is this truth or a ploy planned beneath your red dust as cover in a battlefield of surprises Or did the messenger withhold your secrets forced into lying carlyle miller
MARS (PLANET) Mars is the fourth planet from the Sun in the SOLAR SYSTEM, the next one beyond Earth's orbit. Its red color inspired the Greeks and Romans to name it after their god of war, Ares, or Mars. The distance of Mars from Earth, and hence its brightness, vary considerably. At times it is the third-brightest object in the night sky, surpassed only by the Moon and Venus. PHYSICAL CHARACTERISTICS The orbit of Mars lies about 1.5 times as far away from the Sun as the Earth's does. The orbit is somewhat elliptical, so the planet's distance from the Sun varies from a minimum, at perihelion, of 206.7 million km (128.4 million mi) to a maximum, at aphelion, of 249.2 million km (154.8 million mi). Because Mars is farther from the Sun than Earth is, it takes longer to complete a revolution. Its year is 687 Earth days long. Mars speeds along at 24 km/sec (15 mi/sec) in the same counterclockwise direction (when viewed from above the planet's north pole) as all the other planets. The Martian day is 24 hours, 37 minutes, and 23 seconds long. The present tilt of the planet's axis is about 25 deg, producing seasonal changes similar to those on Earth. Because of the elliptical orbit of Mars, summer in its southern hemisphere occurs when the planet is nearest the Sun, as does winter in its northern hemisphere. The planet has an average diameter of 6,780 km (4,217 mi), making it about half the size of Earth but nearly twice the size of the Moon. Because of its rotation it is slightly flattened, having an actual diameter of 6,794 km (4,222 mi) at the equator and 6,752 km (4,195 mi) at the poles. The bulk density of the planet (3.9 g/cm3) is lower than that of Earth (5.5 g/cm3). In addition, no measurable magnetic field for Mars has been detected, which indicates that the core is solid and explains why Mars has no radiation belt. The total mass of the planet is only one-tenth that of Earth, and thus Martian gravity is only 38% as strong. Mars is orbited by two irregularly shaped satellites. The larger is named PHOBOS ("fear") and the smaller DEIMOS ("terror"), after attributes personified in Greek mythology as sons of Ares. Each is only a few kilometers wide. The moons are heavily cratered and may be asteroids (see ASTEROID) captured by Mars, or the accumulated remnants of the materials that formed it. ATMOSPHERE AND CLIMATE The major constituents of the Martian atmosphere are carbon dioxide (95.3%), nitrogen (2.7%), and argon (1.6%). Minor amounts of oxygen, carbon monoxide, water vapor, and other trace constituents make up the rest. The average surface pressure of the atmosphere is less than 1/100th of the average surface pressure of Earth's atmosphere, and it varies with season and elevation. The Martian atmosphere undergoes dramatic daily and seasonal temperature changes. It averages about 220 K (-64 deg F) and varies from 145 K (-199 deg F) during the polar night to 300 K (80 deg F) at the equator during midday at perihelion. Although thin and frigid, the Martian atmosphere is very active and complex. Mars and Earth have similar global atmospheric circulation patterns because of their other similarities. In the Martian atmosphere, as in Earth's, warm air rises at the equator, moves poleward, deflects to the east, and then descends at middle latitudes and returns to the equator. At middle to high latitudes, winds blowing from the west contain narrow bands of high winds called jet streams, which produce storm systems near the surface. In addition, Mars has seasonal climate changes driven by solar heating and by the exchange of carbon dioxide between polar ice and frost (discussed below) and the atmosphere. During each Martian hemisphere's fall and winter, carbon dioxide freezes out of the atmosphere to form a frost hood that stretches from the pole to nearly halfway to the equator. As spring comes, strong winds are produced by the temperature contrast, at the edge of the retreating polar cap, between the ice and the sun-heated soil. Augmenting this effect is the hotter southern summer, when the planet is closer to the Sun. The strong southern summer winds lift vast amounts of dust that rise into great storms. These storms have been observed to cover the entire planet. SURFACE FEATURES The color of the Martian surface ranges from orange to brownish black. The darker materials are weathered basaltic rock, and the lighter are iron oxides. As seen from Earth, streaked areas of contrasting brightness commonly form within or around topographic features. Many of them change seasonally in form and size, indicating that most of the surface is covered by thin deposits of dust and sand that are easily transported by winds. Photographs of the Martian surface provided by the U.S. VIKING landers confirm the presence of windblown deposits and also show pebbles and cobbles strewn across the surface. These observations may be typical of most of Mars, as demonstrated by various measurements by both Earth-based and spacecraft instruments. Because Mars has no oceans and hence no sea level, elevations on the planet are referenced to an artificial datum, or average surface level. Using this datum, the topography of Mars can be broadly divided into southern cratered highlands that mostly range from 1 to 5 km (0.6 to 3 mi) above the datum, and relatively smooth northern lowlands--covering nearly 40% of the surface--that range 0 to 3 km (1.9 mi) below it. Superposed on the highlands is the Tharsis rise, more than 3,000 km (1,800 mi) across, which reaches 10 km (6 mi) in elevation and supports several huge volcanic shields. The smaller Elysium rise is as much as 5 km (3 mi) higher than the surrounding lowland plains. The canyon system of Valles Marineris, the largest and deepest known in the solar system, extends for more than 4,000 km (2,500 mi) and has 5 to l0 km (3 to 6 mi) of relief between its floors and the tops of the surrounding plateaus. Two immense circular basins within the southern highlands, Hellas and Argyre, are 1,500 and 800 km (about 900 and 500 km) across and 7 and 2 km (4.3 and 1.2 mi) deep, respectively. Each Martian pole is covered by layered deposits, forming a plateau 1,000 to 1,500 km (600 to 900 mi) across and mostly 2 to 4 km (1.2 to 2.5 mi) thick. The plateaus are partly capped by thin ice sheets. The northern ice cap covers about two-thirds of its plateau, whereas the southern cap covers only about one-fifteenth of its plateau. GEOLOGICAL EVOLUTION Although the overall geologic character of Mars is unique in the solar system, it shares characteristics of both the Moon and Earth. This comes as no surprise, because Mars is similar in composition to both bodies. What does come as a surprise is the immensity of many geologic features on Mars compared with the same kinds of features on Earth. The size can be explained by the lack of plate tectonics on Mars, which tends to relocate centers of mountain-building activity, and by the planet's less erosive atmosphere and climate. Another major difference between the two planets is the catastrophic flooding that has occurred on Mars when its abundant ground water was released in great volumes. Noachian Period The lunarlike, ancient cratered highlands of Mars formed within the Noachian Period, the first billion years of the planet's history. Craters and basins were shaped by impacts of meteorites and comets. Thousands of craters tens of kilometers wide, their raised rims surrounded by heaps of ejected materials, mark this ancient highland landscape. Hellas and Argyre are the largest well-preserved impact basins of the period. Evidence exists for several dozen others, ranging from hundreds to thousands of kilometers across, throughout the highlands and along their border with the lowlands. Stream valleys formed throughout much of the highlands, apparently by seepage of groundwater. Their shallow depth shows that the temperature of near-surface rocks was above the freezing point of water and that the surface was warmer than at present. The higher temperatures probably were caused by heat released from the interior of the planet and by a thicker atmosphere. Water erosion contributed to the overall degradation of the surface, which distinguishes most terrain of this period from younger terrains. During Noachian time the Tharsis rise also began to develop. This occurred through a combination of magma intrusion in the crust, volcanic buildup, and uplift caused by heating and density changes of the crust and mantle rocks. Hesperian Period The intermediate, or Hesperian, period of Martian history saw great changes in the landscape, even though bombardment of the surface had declined rapidly and the atmosphere had thinned and become less effective as an erosional agent. First, extensive fields of very fluid lava flows were emplaced over a third of the planet. Most flows originated from fissures, but a few are associated with broad, low, circular volcanic centers. The flanks of some of these volcanoes are eroded, indicating explosive volcanic activity and fluid erosion triggered by interactions between magma and groundwater. As loss of internal heat caused the planet's surface to contract, buckling of the rocks formed long, low ridges on the solidified lava flows. Meanwhile, the Tharsis grew to much of its present great size, producing extensive systems of faults that span an entire hemisphere of the planet. Distinctive, tongue-shaped lava flows from the Tharsis volcanoes covered millions of square kilometers of the rise. The deeper, linear canyons of Valles Marineris developed as a result of rifting that originated in the Martian mantle. These canyons are some of the major source areas for immense channel systems that extend for thousands of kilometers across a highland region that makes up about 10% of the Martian surface. The channels presumably formed by catastrophic outbursts of millions of cubic kilometers of water, ice, and debris, released from artesian aquifers trapped by ice-rich rocks. Most channels originated from jumbled, blocky terrain produced by collapse of the ground that formerly contained the discharged debris and water. At the terminus of the channels in the northern plains, expanses of sediments were deposited in temporary lakes that ultimately sublimated and disappeared. Amazonian Period Overall geologic activity declined during the youngest, or Amazonian, period on Mars, but not before the major development of immense volcanoes on the Tharsis and Elysium rises. Most of the volcanoes form large shields having summit calderas and made up of basaltic lava flows, similar to the Hawaiian volcanos. The largest shield, Olympus Mons, is more than 15,900 m (52,000 ft) high and 600 km (370 mi) across, having roughly the same area as the state of Arizona. Along the canyon walls of Valles Marineris, huge landslides dumped millions of tons of debris across canyon floors. Wind continues to reshape the Martian surface. It has produced an immense "sand sea" of dunes surrounding the north polar plateau. Both polar plateaus appear to be made up of layered deposits of dust and ice that are easily eroded and redeposited by solar heating and wind. PAST AND FUTURE STUDIES OF MARS Mars played an important role in resolving the orbital motions of the planets, because of its puzzling looping motion in the heavens as viewed from Earth. When Johannes Kepler determined in 1609 that the orbital path of Mars is elliptical, he abolished the older Ptolemaic theories based on circular orbits of the planets. The very next year, Galileo made the first telescopic observations of the planet and recorded its phases. In the late 1600s other scientists made closer observations of Mars, determining that its rotational period is close to Earth's, that it has polar caps that show seasonal change, and that dark areas could be distinguished. These were thought to be seas. In the late 1700s, William Herschel noted bright, changing patches that he thought were clouds, suggesting that the planet had an atmosphere. He and later astronomers therefore shared the view that life thrives on Mars. In the late 1800s astronomers also began to observe linear markings--termed "canali" by Giovanni Schiaparelli, though he simply meant channels and not "canals"--that connected broad, dark areas. These observations increased speculation about intelligent life on Mars, culminating in the popularization of this idea by Percival LOWELL. (The "canali" are now known not to be real features but probably to result from a visual illusion in which dark areas appear connected by lines.) The Martian satellites were discovered by Asaph Hall in 1877. Knowledge of the planet has greatly increased through spacecraft missions, beginning with MARINER 4 in 1965 and the Mariner 6 and 7 flybys in 1969. The highly successful Mariner 9 mission in 1971-72, and the Viking Orbiters launched in 1976 together imaged the entire Martian surface and revealed the geologic diversity of the planet. The Viking landers made long-term observations of the surface and atmosphere and performed experiments to determine the composition of surface materials. Their biological experiments found no evidence of organic material. Its apparent absence, together with the planet's thin, dry atmosphere, have led most researchers to believe that no near-surface life exists on Mars. Hospitable conditions for life may be present, however, in warm, wet subterranean environments, if such exist. Other scientists think that life may have existed early in Mars's history, when climate conditions were probably more favorable. Spacecraft missions will continue to be the most productive source of new data for Mars, although the rare SNC (shergottite-nakhlite-chassignite) class of meteorites collected on Earth are pieces of basaltic rock that are thought to have been ejected from Mars by impacts. Various spacecraft missions are in the planning stage. They include landers capable of sophisticated on-site measurements, sample return, seismic detection, and roving, robotic investigation. Such studies are expected to provide further insight into the planet's composition, structure, atmosphere, and possible biology, as well as to open the door for human exploration of the planet. Bibliography: Carr, Michael, The Surface of Mars (1984); Ezell, E. C. and L. N., On Mars (1984); Hartmann, W. K., "What's New on Mars?" Sky and Telescope, May 1989; Haberle, R. M., "The Climate of Mars," Scientific American, May 1986; Hoyt, W. G., Lowell and Mars (1976); Kieffer, H. H., et al., Mars (1992); Miles, Frank, and Booth, Nicholas, Race to Mars (1988); Schultz, Peter H., "Polar Wandering on Mars," Scientific American, December 1985; Wilford, John Noble, Mars Beckons: The Mysteries, the Challenges, the Expectations of Our Next Great Adventure in Space (1990). CHARACTERISTICS OF MARS ------------------------------------- Mean distance from Sun: 227,900,000 km (141,600,000 mi) Length of year: 687 days Length of day: 24 h, 37 min, 23 sec Inclination of axis: 23 degrees 59' Equatorial diameter: 6,787 km (4,210 mi) Mass compared to Earth: 0.107 Specific density (water=1): 3.9 Atmosphere: 95% carbon dioxide, 2% Argon, 3% nitrogen Mean surface temperature: -23 degrees C (-19 degrees F) Satellites: 2 -------------------------------------
Mars: 1995 exploration
Mars: Viking 1
Mars: Viking 2