AstronomyAstronomers have at last found definitive evidence that the universe's first dust - the celestial stuff that seeded future generations of stars and planets - was forged in the explosions of massive stars.
The findings, made with NASA's Spitzer Space Telescope, are the most significant clue yet in the longstanding mystery of where the dust in our very young universe came from. Scientists had suspected that exploding stars, or supernovae, were the primary source, but nobody had been able to demonstrate that they can create copious amounts of dust - until now. Spitzer's sensitive infrared detectors have found 10,000 Earth masses worth of dust in the blown-out remains of the well-known supernova remnant Cassiopeia A.
Space dust is everywhere in the cosmos, in our own neck of the universe and all the way back billions of light-years away in our infant universe. Developing stars need dust to cool down enough to collapse and ignite, while planets and living creatures consist of the powdery substance. In our nearby universe, dust is pumped out by dying stars like our sun. But back when the universe was young, sun-like stars hadn't been around long enough to die and leave dust.
That's where supernovae come in. These violent explosions occur when the most massive stars in the universe die. Because massive stars don't live very long, theorists reasoned that the very first exploding massive stars could be the suppliers of the unaccounted-for dust. These first stars, called Population III, are the only stars that formed without any dust.
The terrestrial planets are the four innermost planets in the solar system, Mercury, Venus, Earth and Mars. They are called terrestrial because they have a compact, rocky surface like the Earth’s. The planets, Venus, Earth, and Mars have significant atmospheres while Mercury has almost none. The following diagram shows the approximate distance of the terrestrial planets to the Sun.
Jupiter, Saturn, Uranus, and Neptune are known as the Jovian (Jupiter - like) planets, because they are all gigantic compared with Earth, and they have a gaseous nature like Jupiter. The Jovian planets are also referred to as the gas giants, although some or all of them might have small solid cores. The following diagram shows the approximate distance of the Jovian planets to the Sun.
This image of our galaxy, the Milky Way, was taken with NASA’s Cosmic Background Explorer’s (COBE) Diffuse Infrared Background Experiment (DIRBE). This never-before-seen view shows the Milky Way from an edge-on perspective with the north pole at the top, the south pole at the bottom and the galactic center at the center. The picture combines images obtained at several near-infrared wavelengths. Stars within our galaxy are the dominant source of light at these wavelengths. Even though our solar system is part of the Milky Way, the view looks distant because most of the light comes from the population of stars that are closer to the galactic center than our own Sun.
The Andromeda Galaxy, M31, is located 2.3 million light years away, making it the nearest major galaxy to our own Milky Way. M31 dominates the small group of galaxies (of which our own Milky Way is a member), and can be seen with the naked eye as a spindle-shaped “cloud” the width of the full Moon. Like the Milky Way, M31 is a giant spiral-shaped disk of stars, with a bulbous central hub of older stars. M31 has long been known to have a bright and extremely dense grouping of a few million stars clustered at the very center of its spherical hub.
This image shows the Sun and nine planets approximately to scale. The order of these bodies are: Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
This image shows the terrestrial planets Mercury, Venus, Earth and Mars approximately to scale. The terrestrial planets are compact, rocky, Earth - like planets.
This image shows the Jovian planets Jupiter, Saturn, Uranus and Neptune approximately to scale. The Jovian planets are named because of their gigantic Jupiter-like appearance.
On February 14, 1990, the cameras of Voyager 1 pointed back toward the Sun and took a series of pictures of the Sun and the planets, making the first ever “portrait” of our solar system as seen from the outside. This image is a diagram of how the frames for the solar system portrait were taken.
This image shows the series of pictures of the Sun and the planets taken on February 14, 1990, for the solar system family portrait as seen from the outside. In the course of taking this mosaic consisting of a total of 60 frames, Voyager 1 made several images of the inner solar system from a distance of approximately 6.4 billion kilometers and about 32° above the ecliptic plane. Thirty-nine wide angle frames link together six of the planets of our solar system in this mosaic. Outermost Neptune is 30 times further from the Sun than Earth. Our Sun is seen as the bright object in the center of the circle of frames. The insets show the planets magnified many times.
These six narrow-angle color images were made from the first ever “portrait” of the solar system taken by Voyager 1, which was more than 6.4 billion kilometers from Earth and about 32° above the ecliptic. Mercury is too close to the Sun to be seen. Mars was not detectable by the Voyager cameras due to scattered sunlight in the optics, and Pluto was not included in the mosaic because of its small size and distance from the Sun. These blown-up images, left to right and top to bottom are Venus, Earth, Jupiter, Saturn, Uranus, and Neptune.
Our solar system consists of an average star we call the Sun, the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes: the satellites of the planets (Moons); numerous comets, asteroids, and meteoroids; and the interplanetary medium.
The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The Sun’s nearest known stellar neighbor is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away.
The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky Way.
The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere. They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The nearest large galaxy is the Andromeda Galaxy. It is a spiral galaxy like the Milky Way but is 4 times as massive and is 2 million light years away. Our galaxy, one of billions of galaxies known, is traveling through intergalactic space.
The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits. When looking down from above the Sun’s north pole, the planets orbit in a counter-clockwise direction. The planets orbit the Sun in or near the same plane, called the ecliptic.
Pluto is a special case in that its orbit is the most highly inclined (18 degrees) and the most highly elciptical of all the planets. Because of this, for part of its orbit, Pluto is closer to the Sun than is Neptune.
The axis of rotation for most of the planets is nearly perpendicular to the ecliptic. The exceptions are Uranus and Pluto, which are tipped on their sides.
Viking was the culmination of a series of missions to explore the planet Mars; they began in 1964 with Mariner 4, and continued with the Mariner 6 and 7 flybys in 1969, and the Mariner 9 orbital mission in 1971 and 1972.
Viking was designed to orbit Mars and to land and operate on the planet’s surface. Two identical spacecraft, each consisting of a lander and an orbiter, were built.
NASA’s Langley Research Center in Hampton, Virginia, had management responsibility for the Viking project from its inception in 1968 until April 1, 1978, when the Jet Propulsion Laboratory assumed the task. Martin Marietta Aerospace in Denver, Colorado, developed the landers. NASA’s Lewis Research Center in Cleveland, Ohio, had responsibility for the Titan- Centaur launch vehicles. JPL’s initial assignment was development of the orbiters, tracking and data acquisition, and the Mission Control and Computing Center.
NASA launched both spacecraft from Cape Canaveral, Florida — Viking 1 on August 20, 1975, and Viking 2 on September 9, 1975. The landers were sterilized before launch to prevent contamination of Mars with organisms from Earth. The spacecraft spent nearly a year cruising to Mars. Viking 1 reached Mars orbit on June 19, 1976; Viking 2 began orbiting Mars on August 7, 1976.
After studying orbiter photos, the Viking site certification team considered the original landing site for Viking 1 unsafe. The team examined nearby sites, and Viking 1 landed on July 20, 1976, on the western slope of Chryse Planitia (the Plains of Gold) at 22.3 degrees North latitude, 48.0 degrees longitude.
The site certification team also decided the planned landing site for Viking 2 was unsafe after it examined high-resolution photos. Certification of a new landing site took place in time for a Mars landing on September 3, 1976, at Utopia Planitia, at 47.7 degrees North latitude, and 48.0 degrees longitude.
The Viking mission was planned to continue for 90 days after landing. Each orbiter and lander operated far beyond its design lifetime. Viking Orbiter 1 exceeded four years of active flight operations in Mars orbit.
The Viking project’s primary mission ended November 15, 1976, 11 days before Mars’s superior conjunction (its passage behind the Sun). After conjunction, in mid-December 1976, controllers re-established telemetry and command operations, and began extended-mission operations.
The first spacecraft to cease functioning was Viking Orbiter 2 on July 25, 1978; the spacecraft had used all the gas in its attitude-control system, which kept the craft’s solar panels pointed at the Sun to power the orbiter. When the spacecraft drifted off the Sun line, the controllers at JPL sent commands to shut off power to Viking Orbiter 2’s transmitter.
Viking Orbiter 1 began to run short of attitude-control gas in 1978, but through careful planning to conserve the remaining supply, engineers found it possible to continue acquiring science data at a reduced level for another two years. The gas supply was finally exhausted and Viking Orbiter 1’s electrical power was commanded off on August 7, 1980, after 1,489 orbits of Mars.
The last data from Viking Lander 2 arrived at Earth on April 11, 1980. Lander 1 made its final transmission to Earth Nov. 11, 1982. Controllers at JPL tried unsuccessfully for another six and one-half months to regain contact with Viking Lander 1. The overall mission came to an end May 21, 1983.
With a single exception — the seismic instruments — the science instruments acquired more data than expected. The seismometer on Viking Lander 1 would not work after landing, and the seismometer on Viking Lander 2 detected only one event that may have been seismic. Nevertheless, it provided data on wind velocity at the landing site to supplement information from the meteorology experiment, and showed that Mars has very low seismic background.
The three biology experiments discovered unexpected and enigmatic chemical activity in the Martian soil, but provided no clear evidence for the presence of living microorganisms in soil near the landing sites. According to mission biologists, Mars is self-sterilizing. They believe the combination of solar ultraviolet radiation that saturates the surface, the extreme dryness of the soil and the oxidizing nature of the soil chemistry prevent the formation of living organisms in the Martian soil. The question of life on Mars at some time in the distant past remains open.
The landers’ gas chromatograph/mass spectrometer instruments found no sign of organic chemistry at either landing site, but they did provide a precise and definitive analysis of the composition of the Martian atmosphere and found previously undetected trace elements. The X-ray fluorescence spectrometers measured elemental composition of the Martian soil.
Viking measured physical and magnetic properties of the soil. As the landers descended toward the surface they also measured composition and physical properties of the Martian upper atmosphere.
The two landers continuously monitored weather at the landing sites. Weather in the Martian midsummer was repetitious, but in other seasons it became variable and more interesting. Cyclic variations appeared in weather patterns (probably the passage of alternating cyclones and anticyclones). Atmospheric temperatures at the southern landing site (Viking Lander 1) were as high as -14°C at midday, and the predawn summer temperature was -77°C. In contrast, the diurnal temperatures at the northern landing site (Viking Lander 2) during midwinter dust storms varied as little as 4°C on some days. The lowest predawn temperature was -120°C, about the frost point ofcarbon dioxide. A thin layer of water frost covered the ground around Viking Lander 2 each winter.
Barometric pressure varies at each landing site on a semiannual basis, because carbon dioxide, the major constituent of the atmosphere, freezes out to form an immense polar cap, alternately at each pole. The carbon dioxide forms a great cover of snow and then evaporates again with the coming of spring in each hemisphere. When the southern cap was largest, the mean daily pressure observed by Viking Lander 1 was as low as 6.8 millibars; at other times of the year it was as high as 9.0 millibars. The pressures at the Viking Lander 2 site were 7.3 and 10.8 millibars. (For comparison, the surface pressure on Earth at sea level is about 1,000 millibars.)
Martian winds generally blow more slowly than expected. Scientists had expected them to reach speeds of several hundred kilometers an hour from observing global dust storms, but neither lander recorded gusts over 120 kilometers an hour, and average velocities were considerably lower. Nevertheless, the orbiters observed more than a dozen small dust storms. During the first southern summer, two global dust storms occurred, about four Earth months apart. Both storms obscured the Sun at the landing sites for a time and hid most of the planet’s surface from the orbiters’ cameras. The strong winds that caused the storms blew in the southern hemisphere.
Photographs from the landers and orbiters surpassed expectations in quality and quality. The total exceeded 4,500 from the landers and 52,000 from the orbiters. The landers provided the first close-up look at the surface, monitored variations in atmospheric opacity over several Martian years, and determined the mean size of the atmospheric aerosols. The orbiter cameras observed new and often puzzling terrain and provided clearer detail on known features, including some color and stereo observations. Viking’s orbiters mapped 97 percent of the Martian surface.
The infrared thermal mappers and the atmospheric water detectors on the orbiters acquired data almost daily, observing the planet at low and high resolution. The massive quantity of data from the two instruments will require considerable time for analysis and understanding of the global meteorology of Mars. Viking also definitively determined that the residual north polar ice cap (that survives the northern summer) is water ice, rather than frozen carbon dioxide (dry ice) as once believed.
Analysis of radio signals from the landers and the orbiters — including Doppler, ranging and occultation data, and the signal strength of the lander-to-orbiter relay link — provided a variety of valuable information.
Other significant discoveries of the Viking mission include:
The human exploration of Mars will be an enterprise that confirms the potential for humans to leave their home planet and make their way outward into the cosmos. Though just a small step on a cosmic scale, it will be a significant one for humans, because it will require going away from Earth with very limited capability to return. Once committed to a journey to Mars, astronauts will not be able to return until the alignment of the planets allows their return. This is the most radical difference between this exploration and all previous explorations. There is a very narrow window within which return is possible, and the commitment to launch is a commitment to three years in space.
Mars is an intriguing and exciting planet, and there are many adventures and findings that await explorers. We must prepare for these before we go, providing the tools that the explorers will use, anticipating as much as possible the situations they will encounter and preparing them for the unexpected. For the first time in a space exploration mission, it will be up to the crew to solve their own emergency problems. At the distance of Mars from the Earth, it can be as much as 40 minutes from the time a message goes out from Earth to the time an answer is received back on Earth. The crews and their systems must be able to accomplish their objectives in a highly autonomous manner.
Mars is an intriguing planet, for what it can tell us about the origin and history of planets and of life. Visible to the ancients, and distinctly reddish in the night sky, the next planet has always been an attractive subject for imaginative science fiction. As the capability for space exploration grew in the 1960’s, it became clear that Mars is not, like Earth, a planet teeming with life, and is now a hostile environment for humans. The images of Mariner 4 showed a Moon-like terrain, dominated by large impact craters. This terrain now is believed to an represent ancient crust, similar to the Moon’s, formed in an initial period of planetary differentiation. Mariner 9 showed for the first time that Mars was not totally Moon-like, but exhibits later volcanic and tectonic features. Large volcanos of relatively recent activity and large crustal rifts due to tensional forces demonstrate the working of internal forces. The absolute time scale is not accurately calibrated, however, by analogy with the Moon, the initial crustal formation may have occurred between 4 billion and 4.5 billion years ago, and the apparent freshness of the large Martian volcanos suggests their formation within the last billion years.
Mars’ atmosphere consists largely of carbon dioxide, with a typical surface pressure of about .01 Earth atmospheres, and surface temperatures that may reach 25°C on the equator in mid-summer, but are generally much colder. At these pressures and temperatures, water can not exist in liquid form on the surface. However, Mariner 9 and the subsequent Viking missions observed features which indicate that liquid water has been present on Mars’ surface in past epochs. Evidence of both running water and standing water has been noted. The interpretation is that the atmosphere of Mars was thicker and warmer in former times, and perhaps much like the Earth’s early atmosphere before the appearance of oxygen.
Three questions arise:
These three scientific questions are at the core of the Mars scientific exploration defined by the Reference Mission. They can all be addressed principally by understanding the geological characteristics of the planet - the types of rocks present, their absolute and relative ages, the distribution of subsurface water, the history of volcanic activity, the distribution of life-forming elements and compounds, and others. These attributes all have to be understood in the context of what we know about the Earth, Moon and other bodies of our solar system.
The dream of human exploration of Mars is intimately tied to the belief that new lands create new opportunities. In human history, migrations of people have been stimulated by overcrowding, exhaustion of resources, the search for religious or economic freedom, competitive advantage, and other human concerns. Rarely have humans entered new territory, then completely abandoned it. In the past, there have always been a few people who were adventurous enough to adopt a newly-found territory as their home. Most of these settlements have eventually become economically self-sufficient, and have enlarged the genetic and economic diversity of humanity. The technological revolution of the 20th Century, with high speed communication and transportation and integrated economic activity, has reversed the trend toward human diversity; however, settlement of the planets can once again enlarge the sphere of human action and life.
The settlement of Mars presents new problems and challenges. Principal among these is the absence of a livable natural environment. That, and the current high cost of transportation are the main barriers to human expansion there. The fact that humans, once on Mars, can not easily return to the Earth, and then only at specified times approximately 26 months apart, makes it necessary to develop systems with high reliability and robustness. The creation of a livable, artificial environment, is technically feasible. The high cost of transportation will ultimately be reduced. The Reference Mission is not a program to settle Mars; however, the objectives of the Reference Mission are to establish the feasibility of and the technological basis for human settlement of the planet.
The space age gained its start in a period of intense technical and social competition between east and west, represented by the Soviet Union and the United States. Competition during the International Geophysical Year resulted in the Soviet Union being the first to launch a satellite into Earth orbit, and served as a challenge and reminder to the United States that technological supremacy was not solely the province of the United States. The start of the Apollo program was a political decision based more on the perception of the political and technological rewards to be gained by attacking a truly difficult objective in a constrained time period. The space race began, the United States won it, and a few years later, the Soviet Union had collapsed.
Fortunately, the Russians did not view the Apollo success as a reason to terminate their program, and they continued to develop capabilities that are fully on a par with United States capabilities in many areas. Also, during the post-Apollo time frame, space capability grew in Europe, with the formation of the European Space Agency, in Japan, China and other countries.
The basis has been laid for a truly international approach to Mars exploration. The exploration of Mars should be an international enterprise.
It would exhibit a great vanity for any country to undertake human exploration of Mars alone, particularly when others, who may not now have the required magnitude of capability or financial resources, do have the underlying technological know-how. Mars should be an objective in which all humanity can share. An underlying requirement for the Reference Mission is that it be implemented by a multinational group of nations and explorers.
Deimos [DEE-mos] (panic) is a moon of Mars and was named after an attendant of the Roman war god Mars. Deimos is a dark body that appears to be composed of C-type surface materials. It is similar to the C-type (blackish carbonaceous chondrite) asteroids that exist in the outer asteroid belt. Some scientists speculate that Deimos and Phobos (the other martian moon), are captured asteroids; however, other scientists present arguments counter to this theory. Both Deimos and Phobos are saturated with craters. Deimos has a smoother appearance caused by partial filling of some of its craters. Asaph Hall discovered Deimos in 1877.
| Characteristic | Measurement |
|
Mass (kg) |
1.8e+15 |
|
Mass (Earth = 1) |
3.0120e-10 |
|
Radius (km) |
7.5×6.1×5.5 |
|
Radius (Earth = 1) |
1.1759e-03 |
|
Mean density (gm/cm^3) |
1.7 |
|
Mean distance from Mars (km) |
23,460 |
|
Rotational period (days) |
1.26244 |
|
Orbital period (days) |
1.26244 |
|
Mean orbital velocity (km/sec) |
1.36 |
|
Orbital eccentricity |
0.00 |
|
Orbital inclination |
0.9-2.7° |
|
Escape Velocity (km/sec) |
0.0057 |
|
Visual geometric albedo |
0.07 |
|
Magnitude (Vo) |
12.40 |
Measuring 16 by 12 kilometers, Deimos circles Mars every 30 hours. Craters of varying age dot its surface, which is somewhat smoother than the surface of Phobos.
This image was taken by the Viking Orbiter spacecraft in 1977.
This image shows a slightly different view of Deimos. It was acquired by the Viking Orbiter spacecraft.
This image is a photomosaic of Deimos, the outer satellite of Mars. The leading side faces forwards in the orbit of Deimos. The trailing side faces backwards along the orbit. Longitude 0 is at the blunter end with the most prominent craters, and faces Mars. As with all conformal (true shape) projections, the scale in these maps varies, increasing from the center to the outer edge.
Phobos [FOH-bohs] (fear) is a moon of Mars and was named after an attendant of the Roman war god Mars. Phobos is a dark body that appears to be composed of C-type surface materials. It is similar to the C-type (blackish carbonaceous chondrite) asteroids that exist in the outer asteroid belt. Some scientists speculate that Phobos and Mars’ other moon, Deimos, are captured asteroids. However, other scientists point to evidence that contradicts this theory. Phobos shows striated patterns which are probably cracks caused by the impact event of the largest crater on the moon. Asaph Hall discovered Phobos in 1877.
| Characteristic | Measurement |
|
Mass (kg) |
1.08e+16 |
|
Mass (Earth = 1) |
1.8072e-09 |
|
Radius (km) |
13.5×10.8×9.4 |
|
Radius (Earth = 1) |
2.1167e-03 |
|
Mean density (gm/cm^3) |
2.0 |
|
Mean distance from Mars (km) |
9,380 |
|
Rotational period (days) |
0.31910 |
|
Orbital period (days) |
0.31910 |
|
Mean orbital velocity (km/sec) |
2.14 |
|
Orbital eccentricity |
0.01 |
|
Orbital inclination |
1.0° |
|
Escape velocity (km/sec) |
0.0103 |
|
Visual geometric albedo |
0.06 |
|
Magnitude (Vo) |
11.3 |
This image was taken by the Viking Orbiter spacecraft in 1977. Striated patterns can be seen in this image. These are probably cracks caused by the impact event of the Stickney crater shown below.
One of the most striking features of Phobos, aside from its irregular shape, is its giant crater Stickney. Because Phobos is only 28 by 20 kilometers, the moon must have been nearly shattered from the force of the impact that caused the giant crater. Grooves that extend across the surface from Stickney appear to be surface fractures caused by the impact. Near the crater, the grooves measure about 700 meters across and 90 meters deep. However, most of the grooves have widths and depths in the 100 to 200 meters and 10 to 20 meters ranges, respectively.
This image shows a slightly different view of the Stickney crater. A crater within the Stickney crater is visible.
This shows two different views of Phobos in a Morphographic Conformal Projection. One view shows the leading side and the other the trailing side.
Although not as pronounced as on Earth, clouds are common features on Mars. The Martian atmosphere has only a trace of water vapor; however, the temperature and pressure is such that the atmosphere is usually close to saturation and produces clouds. Even from Earth based telescopes, clouds have been observed by transient brightening on the surface of Mars. Numerous cloud patterns have been seen from the Mariner and Viking spacecraft and have been classified into various categories (Carr, 1981; French et al. 1981):
Lee waves. These clouds form in the lee of large obstacles such as mountains, ridges, craters and volcanoes. The air in these regions undergoes wavelike oscillations.
Wave clouds. These clouds appear as rows of linear clouds. They are common at the edge of the polar caps.
Cloud streets. These clouds exhibit a double periodicity. They appear as linear rows of cumulus-like, bubble-shaped clouds.
Streaky clouds. These clouds have a direction without periodicity.
Fog or ground hazes. Fog usually occurs in low areas such as valleys, canyons and craters. It forms during the coolest times of the day such as dawn and dusk. Sometimes ground haze is caused by dust in the atmosphere; however, if the atmosphere is clear ground fog can be easily identified.
Plumes. These are elongated clouds. They appear to have a source of rising material and in many case are composed of dust particles.
Along the edge of the polar cap, cyclonic disturbances are common during the late summer and fall. This storm system is located at the edge of the northern polar cap. In the foreground, frost can be seen as bright areas.
This is a good example of a lee wave associated with an impact crater. Note the wave periodicity in the clouds.
Wave clouds usually occur at the lee of a large obstacle. They are often found at the edge of the polar cap, and in the Tharsis and Lunae Planum regions.
The cloud patterns illustrated by this image exhibits a double periodicity. These types of clouds usually occur close to the northern-polar cap and in the Tharsis and Syria Planum regions.
Streaky clouds seem to be found most everywhere; however, they seem to be more concentrated in the highlands southwest of Syrtis Major.
Fog often appears in low-lying areas. It typically occurs in the southern hemisphere especially in the Argyre and Hellas basins. It forms frequently in craters. Occasionally, it occurs in higher regions such as Sinus Sabaeus and Solis Planum.
This image shows early morning fog in the Noctis Labyrinthis, at the westernmost end of Valles Marineris. This fog, which is probably composed of water ice, is confined primarily to the low-lying troughs, but occasionally extends over the adjacent plateau. The region shown is about 300 kilometers across.
This is an example of a dust plume in the Solis Planum region. This image was taken during the springtime for this region. Plumes are found primarily in the southern hemisphere, in highlands such as Syrtis Major and in elevated regions such as Tharsis.
Mars is only about one-half the size of Earth and yet has several volcanoes that surpass the scale of the largest terrestrial volcanoes. The most massive volcanoes are located on huge uplifts or domes in the Tharsis and Elysium regions of Mars. The Tharsis dome is 4,000 kilometers across and rises to 10 kilometers in height. Located on its northwest flank are three large shield volcanoes: Ascraeus Mons, Pavonis Mons and Arsia Mons. Beyond the dome’s northwest edge is Olympus Mons, the largest of the Tharsis volcanoes. Olympus Mons is classified as a shield volcano. It is 24 kilometers high, 550 kilometers in diameter and is rimmed by a 6 kilometers high scarp. It is one of the largest volcanoes in the Solar System. By comparison the largest volcano on Earth is Mauna Loa which is 9 kilometers high and 120 kilometers across.
Elysium Planitia is the second largest volcanic region on Mars. Elysium Planitia is centered on a broad dome that is 1,700 by 2,400 kilometers in size. It has smaller volcanoes than the Tharsis region, but a more diverse volcanic history. The three volcanoes include Hecates Tholus, Elysium Mons and Albor Tholus.
The large shield volcanoes on Mars resemble Hawaiian shield volcanoes. They both have effusive eruptions which are relatively quiet and basaltic in nature. Both have summit pits or calderas and long lava flows or channels. The biggest difference between Martian and Terrestrial volcanoes is size. The volcanoes in the Tharsis region are 10 to 100 times larger than those on Earth. They were built from large magma chambers deep within the Martian crust. The Martian flows are also much longer. This is probably due to larger eruption rates and to lower gravity. One of the reasons volcanoes of such magnitude were able to form on Mars is because the hot volcanic regions in the mantle remained fixed relative to the surface for hundreds of millions of years. On Earth, the tectonic flow of the crust across the hot volcanic regions prevent large volcanoes from forming. The Hawaiian islands were created as the Pacific plate moved northwest. These volcanoes have a relatively short life time. As the plate moves new volcanoes form and the old ones become silent.
Not all Martian volcanoes are classified as shields with effusive eruption styles. North of the Tharsis region lies Alba Patera. This volcano is comparable to Olympus Mons in its horizontal extent but not in height. Its base diameter is 1,500 kilometers but is less than 7 kilometers high. Ceraunius Tholus is one of the smaller volcanoes. It is about the size of the Big Island of Hawaii. It exhibits explosive eruption characteristics and probably consists of ash deposits. Tyrrhena Patera and Hadriaca Patera both have deeply eroded features which indicate explosive ash eruptions. Mt. Saint Helens is an example of a terrestrial ash eruption.
This set of images was chosen to show some of the best examples of volcanic landforms on Mars.
The alignment of the three shield volcanoes that make up the Tharsis [THAR-siss] Montes region is clearly evident in this view. They are named Ascraeus Mons (top right), Pavonis Mons (middle) and Arsia Mons (bottom). Olympus Mons can be seen in the upper left hand corner. The three volcanoes are each somewhat smaller than Olympus Mons, varying from 350 to 450 kilometers in horizontal extent and each rising about 15 kilometers above the surrounding plains. The Tharsis Montes are located on the crest of a broad uplift of the Martian crust so that their summits are at about the same elevation as the summit of Olympus Mons. The fractures southeast of Pavonis Mons are named Noctis Labyrinthus; this region merges with the enormous Vallis Marineris canyon system to the east.
This image shows a computer simulation of processes in the interior of Mars that could have produced the Tharsis region. The color differences are variations in temperature. Hot regions are red and cold regions are blue and green, with the difference between the hot and cold regions being as much as 1000°C. Because of thermal expansion, hot rock has a lower density than cold rock. These differences in density cause the hot material to rise toward the surface and the cold material to sink into the interior, creating a large-scale circulation known as mantle convection. This type of mantle flow produces plate tectonics on Earth. The hot, rising material tends to push the surface of the planet up, and the cold, sinking material tends to pull the surface down. These motions contribute to the overall topography of the planet. This deformation of the planet’s surface is shown in gray along the outer surface of the planet in this image. The amount of deformation is highly exaggerated to make it visible here. The actual uplift in Tharsis is estimated to be about 8 kilometers at its center. This uplift also stretches the crust, forming features such as grabens and Valles Marineris. In addition, the hot, rising material may melt as it approaches the surface, producing volcanic activity.
Elysium Planitia is the second largest volcanic region on Mars. It is located on a broad dome that is 1,700 by 2,400 kilometers in size. The volcanoes Hecates Tholus, Elysium Mons and Albor Tholus can be seen going from north to south (top to bottom) in this image. Hectas Tholus is 160 by 175 kilometers in size with a caldera complex 11.3 by 9.1 kilometers in size. Elysium Mons is the largest volcano in this region. It has base dimensions of 420 by 500 by 700 kilometers and rises 13 kilometers above the surrounding plains. Its summit caldera is about 14.1 kilometers in diameter. Albor Tholus measures 160 by 150 kilometers with a summit caldera of 35 by 30 kilometers. Its northwest flanks have been partially buried by lava flows from Elysium Mons.
Olympus [oh-LIM-pus] Mons is the largest volcano known in the solar system. It is classified as a shield volcano, similar to volcanoes in Hawaii. The central edifice of Olympus Mons has a summit caldera 24 kilometers above the surrounding plains. Surrounding the volcano is an outward-facing scarp 550 kilometers in diameter and several kilometers high. Beyond the scarp is a moat filled with lava, most likely derived from Olympus Mons. Farther out is an aureole of characteristically grooved terrain, just visible at the top of the frame.
This 3D image of Olympus Mons was created from several images taken from different spacecraft positions and combined with a computer model of the surface topography. The final mosaic shows Olympus as it would be seen from the northeast. It is possible that volcanoes of such magnitude were able to form on Mars because the hot volcanic regions in the mantle remained fixed relative to the surface for hundreds of millions of years.
This complex caldera is composed of several discrete centers of collapse where the older collapse features are cross-cut by more recent collapse events. The lowermost circular floor preserves the last lava flooding event that followed the last major collapse. The southern wall of the caldera has at least 3 kilometers of vertical relief with an average slope of at least 26° (from horizontal). The caldera complex truncates several lava flows, indicating that the flows predate the collapse event and that their source areas have been destroyed by the caldera formation.
The caldera on Arsia Mons is considerably larger than the calderas on either Ascraeus Mons or Pavonis Mons. However, the last major collapse event on Arsia Mons was followed by a substantial outpouring of lava within the caldera. The caldera rim has been breached on the southwest side while the caldera floor lavas bury portions of the northeast rim. Aligned between these breaks in the caldera is a series of very subdued domes on the caldera floor, perhaps representing localized sources of the lava that flooded the caldera. The flaks of the shield have been deeply eroded near the locations of the breaks in the caldera rim and lava flows extend away from the volcanoes at these embayments.
This view of Apollinaris Patera, shows characteristics of an explosive origin and an effusive origin. Incised valleys in most of the flanks of Apollinaris Patera indicates ash deposits and an explosive origin. On the west side (left), landslides that have shaped its surface also indicate ash deposits. Towards the south flank, a large fan of material flowed out of the volcano. This indicates an effusive origin. Perhaps during its early development Apollinaris Patera had an explosive origin with effusive eruptions taking place later on.
Ceraunius Tholus (bottom) shows several incised valleys cut into its flanks which indicate that it was easily eroded and probably consists of ash deposits due to explosive activity. The lower flanks of the volcano have been buried beneath the plains material. Ceraunius Tholus is about the size of the Big Island of Hawaii. Uranius Tholus (Top) also shows similar characteristics to Ceraunius Tholus. A major impact crater, just above Ceranius Tholus, postdates the plains material and volcano. However, a prominent delta of probable volcanic material was emplaced within the impact crater at the mouth of a sinuous channel that extends up the flank of Cerauius Tholous to the summit crater. (Credit: Calvin J. Hamilton and Lunar and Planetary Institute)
This is a three dimensional view of Ceraunius Tholus (right) and Uranius Tholus (left). The view is from the northwest.
Tharsis Tholus measures about 150 kilometers across and 8 kilometers high. The east and west flanks are indented giving it a strange appearance. One possible cause for its appearance is that when the lava supply drained away, the center of the volcano collapsed. An alternative is that big slump areas carried off portions of the flanks, giving it the broken appearance.
Uranius Patera is about the size of the Big Island of Hawaii. It is about 3 kilometers in height. It has shallow slopes and lava flows. This indicates an effusive origin. The center caldera was formed when lava drained away and the volcano collapsed.
This feature is an example of a class of volcanoes that are considerably smaller than the broad shield volcanoes. The summit consists of a single, very circular caldera with a smooth floor that predates the ejecta from two large impact craters. The lower flanks of the volcano, including portions of the impact craters, have been buried by the material that makes up the surrounding plains. This superpositional relationship indicates that the plains were emplaced subsequent to both the volcano and the large impact craters on the volcano. The plains are probably made up of lava supplied from Tharsis Montes that flowed down the sides of the broad uplift associated with the Tharsis shields. Both the plains and the volcano are cut by a graben, indicating tectonic activity subsequent to the emplacement of the plains.
This shows perspective view of Ulysses Patera looking from the north.
Volcanoes located within the densely cratered southern highlands have a very different morphology from either the Tharsis or Elysium volcanoes. Tyrrhena Patera has very little vertical relief (< 2 kilometers), resulting in very shallow flank slopes. The flanks of the volcano are deeply eroded with many broad channels that radiate from the summit region. The low relief and easily erodible nature of the flank materials has been interpreted to indicate that the bulk of the volcano is composed of pyroclastic ash deposits. This interpretation implies that the style of eruption for the highland volcanoes like Tyrrhena Patera is significantly different from the repeated effusion of fluid lavas that built up the shield volcanoes.
This shows perspective view of Tyrrhena Patera looking from the north. The vertical dimension has been greatly exaggerated to show detail.
Much like Tyrrhena Patera, Hadriaca Patera is a deeply eroded feature having little vertical relief. Several impact craters are superimposed on the eroded flanks, indicating a great age for this volcano. A large channel has its source near the southeastern margin of the volcano; the fluid that carved the channel flowed southwest into the interior of the Hellas basin.
Volcanic construct on Mars are not all enormous mountains like the Tharsis Montes. This elongate hill surmounted by a linear depression is interpreted to be a product of localized but not extremely voluminous eruptions. If the volcanic material was emplaced by ejection along a ballistic trajectory, this feature may be similar to a terrestrial cinder cone. This feature is aligned with several grabens in the area so that a structural weakness in the crust may have provided the conduit for the volcanic material to reach the surface.
Numerous small mounds having summit craters are found in various locations on Mars. The mounds shown here are east of the Hellas basin. These features have been interpreted to be pseudocraters created by localized phreatic explosions where lava interacts with volatile-rich ground. Most of the mounds are between 400 meters to 1 kilometer across. Many have slotlike summit vents. However, images presently available do not have sufficient resolution to show conclusive evidence of a volcanic origin for the mounds.
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