Martian Clouds
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.
Views of Martian Clouds
Cyclonic Disturbances
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.
Lee Wave
This is a good example of a lee wave associated with an impact crater. Note the wave periodicity in the clouds.
Wave 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.
Cloud Streets
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
Streaky clouds seem to be found most everywhere; however, they seem to be more concentrated in the highlands southwest of Syrtis Major.
Fog
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.
Clouds in Noctis Labyrinthis
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.
Dust Plume
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.
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.
The Lunar Phases (from new, waxing crescent, first quarter, waxing gibbous, full waning gibbous, last quarter, waning crescent and back to new)
Phases of the Moon is at the top of the list of things that students seriously misunderstand. Most teachers run into problems in trying to explain the Moon’s phases to young people, and evidence suggests that many have a very difficult time with the concepts. The problem starts immediately when the teacher uses a light piece of chalk on a dark board. Is he or she making the drawing as a positive or a negative?
Total lunar eclipse of January 20-21, 2000, taken from Prestwich, Manchester, UK by Michael Oates between 1700 hours to 1810 hours.
This full disc of the Moon was photographed by the Apollo 17 crew during their trans-Earth coast homeward following a successful lunar landing mission in December 1972. Mare seen on this photo include Serentatis, Tranquillitatis, Nectaris, Foecunditatis and Crisium. 
This image was taken by Apollo 11 astronauts in 1969. It shows a portion of the Moon’s heavily cratered far side. The large crater is approximately 80 kilometers in diameter. The rugged terrain seen here is typical of the farside of the Moon. 
This mosaic is composed of 1,500 Clementine images of the south polar region of the Moon. The top half of the mosaic faces Earth. Clementine has revealed what appears to be a major depression near the lunar south pole (center), evident from the presence of extensive shadows around the pole. This depression probably is an ancient basin formed by the impact of an asteroid or comet. A significant portion of the dark area near the pole may be in permanent shadow, and sufficiently cold to trap water of cometary origin in the form of ice. The impact basin Schrodinger (near the 4 o’clock position) is a two-ring basin, about 320 kilometers in diameter which is recognized to be the second youngest impact basin on the Moon. The center of Schrodinger is flooded by lavas. A volcanic vent seen in the floor of Schrodinger is one of the largest single explosive volcanoes on the Moon. The Apollo 11 Lunar Module (LM) ascent stage, with Astronauts Neil A. Armstrong and Edwin E. Aldrin Jr. aboard, is photographed from the Command and Service Module (CSM) during rendezvous in lunar orbit. The LM was making its docking approach to the CSM. Astronaut Michael Collins remained with the CSM in lunar orbit while the other two crewmen explored the lunar surface. The large, dark-colored area in the background is Smyth’s Sea, centered at 85 degrees east longitude and 2 degrees south latitude on the lunar surface (nearside). This view looks west. The Earth rises above the lunar horizon. 
Astronaut Edwin E. Aldrin Jr., lunar module pilot, poses for a photograph beside the deployed United States flag during Apollo 11 extravehicular activity on the lunar surface. The Lunar Module Eagle is on the left. The footprints of the astronauts are clearly visible in the soil of the Moon. This picture was taken by Astronaut Neil A. Armstrong, commander, with a 70mm lunar surface camera. 
This view of the Earth rising over the Moon’s horizon was taken from the Apollo 11 spacecraft. The lunar terrain pictured is in the area of Smyth’s Sea on the nearside. 
A close-up view of an astronaut’s footprint in the lunar soil, photographed with a 70mm lunar surface camera during the Apollo 11 extravehicular activity (EVA) on the Moon. 
This is a view of the Lunar Roving Vehicle photographed alone against the desolate lunar background during an Apollo 15 lunar surface extravehicular activity (EVA) at the Hadley-Apennine landing site. This view is looking north. The west edge of Mount Hadley is at the upper right edge of the picture. Mount Hadley rises approximately 4,500 meters above the plain. The most distant lunar feature visible is approximately 25 kilometers away. 
This is the landing site of the last Apollo mission (Apollo 17). It was in the valley among the Taurus-Littrow hills on the southeastern rim of Mare Serenitatis. Astronauts Eugene Cernan and Harrison H. Schmitt explored the valley with the aid of an electrically powered car. This image shows Schmitt inspecting a huge boulder that has rolled down the side of an adjacent hill. 
Earth in the far distant background is seen above a large lunar boulder on the Moon. This photo was taken with a handheld Hasselblad camera by the last two Moon walkers in the Apollo Program. 
This image is an excellent view of the desolate lunar space at Station 4 showing scientist-astronaut Harrison H. Schmitt, lunar module pilot, working at the Lunar Roving Vehicle during the second Apollo 17 extravehicular activity at the Taurus-Littrow landing site. This is the area where Schmitt first spotted the orange soil which is visible on either side of the Lunar Roving Vehicle in this picture. Shorty Crater is to the right, and the peak in the center background is Family Mountain. A portion of South Massif is on the horizon at the left edge. 
These orange glass spheres and fragments are the finest particles ever brought back from the Moon. The particles range in size from 20 to 45 microns. The orange soil was brought back from the Taurus-Littrow landing site by the Apollo 17 crewmen. Scientist-Astronaut Harrison J. Schmitt discovered the orange soil at Shorty Crater. The orange particles, which are intermixed with black and black-speckled grains, are about the same size as the particles that compose silt on Earth. Chemical analysis of the orange soil material has show the sample to be similar to some of the samples brought back from the Apollo 11 (Sea of Tranquility) site
This is an oblique view of the large crater Copernicus on the lunar nearside, as photographed from the Apollo 17 spacecraft in lunar orbit. 
Impact cratering is a process found everywhere in the solar system except on the giant gaseous planets. Earth has been heavily impacted but erosion has removed most of the craters. 
Clouds from Space. Shuttle astronauts are clearly fascinated by the topside view of Earth’s atmospheric patterns that space flight provides, since every space shuttle crew takes a significant number of photographs of clouds. In the past two years, interest in clouds has increased considerably as scientists attempt to understand global warming and the greenhouse effect. Efforts to predict climatic changes associated with global warming have focused new attention on the warming and cooling properties of clouds. The picture is a complex one, involving competing feedback mechanisms, and is not fully understood at this time. All clouds block some fraction of the incoming solar radiation, and absorb some fraction of the heat radiated back from the Earth’s surface, and the balance between these two processes is hard to quantify. However, contemporary thinking suggests that the lower altitude cumulus clouds (such as pictures Thunderstorms, Brazil and Cumulus Cloud Tops) have a net cooling effect on Earth’s surface, reflecting heat back to space. Conversely, the higher, thin cirrus clouds (such as pictures Jet Stream Cirrus and Jet Stream Cirrus, Saudi Arabia) trap heat, reflecting it back to the surface of Earth. 
This photograph taken from about 320 kilometers above the Earth shows a band of cirrus clouds produced by a westerly jet stream that stretches across the Red Sea from Sudan to Saudi Arabia. The contained uniformity of the cloud formation reflects the narrow track of the jet stream moving from left to right across the frame. The shuttle photo shows that the cloud band comprises a series of distinct and precisely spaced roll clouds. These are created by a rolling motion in the upper level air current. 
The shuttle crew approached this storm system from its southern margin in the Gulf of Mexico. The margins are clearly defined. The clouds in the storm system rise to about 16,500 meters. April squall lines,/b> of this type are often associated with tornado development across the southeastern states. 
These cumulus thunderheads near São Paulo, Brazil, where photographed from almost directly overhead by the STS 41-B crew. This perspective conveys something of the energy that drives these cloud columns to punch up into the atmosphere,/b>. The foreshortening resulting from the near-vertical viewing angle disguises the fact that the cloudheads so prominently in view are but the tops of massive thunderhead storm clouds that can tower up to 18,000 meters in the tropics. 
The STS 41-B crew shot this oblique photograph just moments after the previous picture was taken. Some more fully developed thunderheads can be seen in the same Brazilian storm. When the rising cumulus columns meet the tropopause, or base of the stratosphere, at about 15,000 kilometers, they reach a ceiling and can no longer rise buoyantly by convection. The stable temperature of the stratosphere suppresses further adiabatic ascent of moisture that has been driven through the troposphere by the 5-6.8 degree/kilometer lapse rate. Instead, ice clouds spread horizontally into the extended cirrus heads seen in this photograph, forming the “anvil heads” that we identify from the ground. The finer, feathery development around the edges of some of the thunderheads is glaciation - water vapor in the cloud is turning to ice at high altitude. 
All that can be seen in this photograph is cloud stretching several hundred kilometers to the limb of the Earth, yet it tells us a great deal about the water in the Bering Sea below. The line or cloud margin running diagonally across the frame with dense, thick cloud to the right and lighter, more broken cloud to the left reflects an ocean current margin. A difference in water temperature on either side of the margin is reflected in the cloud forms condensing above. This striking cloud boundary stretches for 800-960 kilometers in this photograph. 
Condensing moisture from ocean currents in some parts of the world creates clouds that stay uniformly in position above that current for months at a time. This example shows clouds hanging above the cold Benguela current, which travels northward along the Atlantic coast of southwestern Africa. It is interesting that while the ocean is densely cloud-covered and the clouds lap at the coast, they never cross the coastline. The pinkish-colored Namib Desert is one of the driest places on Earth, confirming that the cloud associated with the ocean current does not stray off its prescribed track. Indeed the Namib Desert is home to unique inhabitants - insects with leg hairs especially adapted to collect moisture from morning dew - a strange irony of life on Earth where moisture-laden clouds hang so closeby. 
These wispy rows of cloud or “cloud lanes” are recognized as a “landmark” by successive shuttle crews. This unique cloud formation off Oman is virtually constant at certain times of year. The clouds are created by a small vortex in the low level wind current. There is little difference between the ocean and atmosphere temperatures here, but the air current may have been subjected to heating from the Somali Current. 
This series of cirrus clouds is know as “roll clouds” because they are sculpted into tight rolls by air currents from the jet stream over Saudi Arabia and the Red Sea. The crest-to-crest spacing of the cloud bands can be used to calculate the velocity of the jet stream. 
This photograph taken over Namibia reveals another effect of jet streams. Here two streams converge; cloud has formed in the corridor between the two streams. Turbulence along the margins of the jet stream may explain the sharp boundary. The point of convergence of the two air streams is precisely located by this photograph. Shadows mark the cloud edges against a sunlit Namibian backdrop. 
Small cumulus clouds frequently form in parallel rows or “cloud streets” in stable air conditions. These cloud streets over the reefs of the Maldive Islands in the Indian Ocean denote the prevailing wind direction, the cloud streets lying parallel with the wind. Turbulent air lifted by the windward portions of the islands promotes cloud formation downwind. 
The combination of warm water temperature and hundreds of square kilometers of ocean, uninterrupted by land masses, results in a regular cumulus and stratocumulus cloud formation. In the Pacific Ocean the Trade Winds propel the clouds from east to west across the ocean. When the air current is intercepted by a sufficiently high land mass, such as the Big Island of Hawaii, the stable cloud pattern is interrupted and the clouds divide to bypass the island in a wide arc forming an “island wake”. In addition to illustrating how gracefully the clouds circumnavigate Hawaii’s volcanic peaks, the photograph shows how the prevailing wind direction dictates that the north and northeast of the island are wetter than the western side of the island and frequently under cloud. The clouds deposit rain on the low ground before dividing and spinning out to sea when they meet the Kohala Mountains and Mauna Kea with its summit at 4,205 meters. 
Islands or high land, elevated above the surroundings and interrupting the air stream, can produce “tails” as well as “wakes.” Shuttle astronauts have frequently observed Dek Island in Lake Tana in Ethiopia, the source of the Blue Nile, with a well-developed cloud tail. This occurs when the land mass disrupts the air flow, creating downwind turbulence that promotes condensation. The lake stands at 1,800 meters above sea level. 
Open cell formations like this are frequently found over ocean. The cells are denser to the left of the frame than to the right, suggesting a gradual warming in water temperature. By looking at this photograph and studying the water color and cloud density, an expert could tell you which ocean you are looking at, the time of year, and the temperature of the water below. This picture was taken in the Indian Ocean, north of Australia. 
This pinwheel of anticyclonic clouds was photographed by the STS 41-B crew over the southern hemisphere of the Pacific Ocean. The ground winds at the center of this cyclonic system reach 80 kilometers per second. Circular storms in the northern hemisphere produce spiraling clouds with a clockwise pattern, while southern latitude storms have a counterclockwise cloud motion. 
During the Solar Maximum Satellite Repair Mission, astronauts had an excellent opportunity to look down the eye of Hurricane Kamysi over the Indian Ocean. Clear blue water can be seen through the hurricane’s eye, and the crew reported that they could see the ocean wave below. Unfortunately, the camera film could not pick them out. 
Odessa is one of the strongest circular storm patterns seen by shuttle crews to date and has a superb tightly formed eye. The tighter the eye in a circular storm, the stronger the winds underneath. Mission STS 51-1 came to be known as the mission of all the hurricanes, tracking no less than four circular storms around the globe. Live pictures from Discovery of Hurricane Elena in the Gulf of Mexico were transmitted directly from Mission Control in Houston to the National Hurricane Center in Florida for correlation with conventional weather satellite and high level aircraft data. 
Space shuttle crews see a sunrise or sunset every 45 minutes as they circle the Earth at 27,300 kilometers per hour, crossing the surface at 6.4 kilometers per second. From their unique perspective they see clearly defined bands of color through the atmosphere as the sun rises. High-peaking cumulus clouds, topping out in anvil-head cirrus can be seen as black shadows against the sunlit horizon. The brightness of the colors in the atmosphere in this photograph taken over the South China Sea is due to concentrations of dust in the atmosphere. Greater concentrations of dust are found in equatorial regions. There are various sources for such upper level dust. Many dust storms in Africa, intensified by several years of drought, have been responsible for putting large amounts of dust into the atmosphere in recent times. Ash clouds from major volcanic eruptions can have a similar effect. Recent discussion of the climatic and environmental effects of a “nuclear winter” centering on upper atmosphere pollution has drawn from the atmospheric effects of catastrophic volcanic eruptions.
The Discovery crew photographed this very distinct stripe running through the clouds for several hundred kilometers. Two weather systems are sliding past each other like crustal plates on the Earth’s surface. The one at the top of the photographM (geographical north) is moving up and curing away slightly to the north, while the system at the bottom of the frame is moving westward and curving gently to the south in conjunction with a cyclone located several hundred kilometers away. The miniature cold-water gyres on the fringes of the two weather systems indicate that a channel of colder water runs under the break in the clouds and is reflected above where colder air runs between the two cloud masses.
Like Sigmund Jähn, those who have gone into space have come back with a changed perspective and reverence for the planet Earth. Gone are the political boundaries. Gone are the boundaries between nations. We are all one people and each is responsible for maintaining Earth’s delicate and fragile balance. We are her stewards and must take care of her for future generations.
The Tibet plateau is the largest and highest elevated region in the world. The plateau is 1,200 kilometers from east to west and 900 kilometers north to south, with a mean elevation of more than 400 meters. Because the plateau rises above so much of the atmosphere, photographs are typically brilliantly crisp and clear. A plethora of geological features are visible in any frame. This picture shows the northwest corner of the plateau near the point where the ground falls away to the Tarim Basin. The impressive snow-capped mountain at top right with well-developed valley glaciers is Muztag Ulu, which has an elevation of 7,282 meters. The plateau was elevated as a consequence of the collision between India and Asia, which resulted in extensive shortening by overthrusting and folding.
This is a radar image of Mount Everest and its surroundings, along the border of Nepal and Tibet. The peak of Mount Everest, the highest elevation on Earth at 8,848 meters, can be seen near the center of each image. It shows an area approximately 70 by 38 kilometers that is centered at 28.0 degrees north latitude and 86.9 degrees east longitude. North is toward the upper left. Many features of the Himalayan terrain are visible in the image. Snow covered areas appear bright blue in the image which was taken in early spring and shows deep snow cover. The curving and branching features seen are glaciers. Radar is sensitive to characteristics of the glacier surfaces that are not detected by conventional photography, such as the ice roughness, water content and stratification. For this reason, the glaciers show a variety of colors (blue, purple, red, yellow, white) but only appear as gray or white in an optical photograph.
This is a radar image of the region around the site of the lost city of Ubar in southern Oman, on the Arabian Peninsula. The ancient city was discovered in 1992 with the aid of remote sensing data. Archeologists believe Ubar existed from about 2800 B.C. to about 300 A.D. and was a remote desert outpost where caravans were assembled for the transport of frankincense across the desert. The prominent, magenta colored area is a region of large sand dunes. The prominent green areas are rough limestone rocks, which form a rocky desert floor. A major wadi, or dry stream bed, runs across the middle of the image and is shown largely in white due to strong radar scattering.
The arid coastal plain that forms the Namib Desert extends the entire length of the Atlantic coast of South West Africa, a total of more than 800 kilometers. Its width varies between 40 and 140 kilometers. The intricate pattern of large sand dunes is caused mainly by dry westerly winds cooled by the offshore Benguela current. Some of the dunes are extremely large, exceeding 300 meters. Running diagonally downward from the upper right corner is a dune-free tongue of alluvial gravel known as the Sossusvlei. This is formed by occasional flash floods draining from the barren, rocky hills on the right of the picture.
The Galapagos archipelago lies 1,000 kilometers west of Ecuador and 1,500 kilometers southwest of the Panama Canal. Geologically the islands sit on the Galapagos rift, an offshoot of the East Pacific Rise. The chain of young volcanic islands - 13 large islands and many smaller ones - straddles the equator, stretches between 1° north and 1°3′ south, and lies between 89 and 92° west longitude. With the exception of Isabella, the largest island, the islands are roughly circular in shape with high volcanic craters at the island centers, that rise to 1,520 meters. Numerous eruptions have taken place on the islands within historic times. However, the detailed geology of the islands is only now coming under investigation, since most are extremely inaccessible. A major eruption on Fernandina Island in 1974 went unnoticed on the ground until it was observed by astronauts aboard the Skylab 4 spacecraft. The islands are largely desolate lava piles with little vegetation along the coastlines. However,
Canton Atoll is a good example of a long-lived coral atoll. Like Tupai, it probably originated as a fringing reef developed around a volcanic island that has long since disappeared. Unlike Tupai, however, it is far distant from any above-surface volcanic structure. Its parent volcano long ago subsided deep beneath the sea. The atoll lies only 2.5° from the equator and is subjected to long periods of drought. Although it is the largest island in the Phoenix group, only 9 square kilometers rise above sea level. The island was discovered in the early 19th century and was named after an American whaling ship wrecked there in 1854. For several decades, American companies extracted the valuable guano. However, in the 20th century, Canton’s attraction was as a refueling stop for aircraft on long-haul flights across the Pacific. Hence, the island has a long runway on the north shore and the designation, on maps, of the lagoon as a seaplane anchorage.However, advances in aircraft design eliminated the island’s role as a refueling stop. With no economic role and insufficient soil to support crops, the island does not support permanent habitation. Patterns of coral heads growing within the shallow water of the lagoon are clearly visible as a thin white network.
This chain of coral-fringed islands forms the Leeward Island chain within the French Society Islands. At bottom right are the islands of Tahaa and Raiatea. They are old, eroded volcanoes, fringed by a coral reef. Northward along the chain, the original central volcanoes are older and more heavily eroded. On Bora Bora (center), the reef is prominently developed and the island significantly eroded. The northernmost island, Tupai, is merely an atoll, having lost any relic of the volcano around which the reef originally grew, except for the shallow floor of the lagoon, showing up in turquoise. This sequence provides an excellent illustration of the hypothesis first propounded by Charles Darwin to explain the origin of coral reefs in deep oceans. Reef-building corals can only live in shallow waters of 20 meters, in temperatures over 21° centigrade. Initially, corals formed fringing reefs around volcanic islands. Old volcanoes are very rapidly eroded in tropical climates until they reach sea level. Below sea level, the rate of erosion is much slower, and atolls such as Tupai might exist for long periods. If for geological reasons the original volcano subsides below sea level at a slow enough rate, corals will continue to build, thus preserving an atoll at the surface long after the original volcanic edifice has been deeply submerged.
The Great Barrier Reef is the largest structure ever built by living organisms. At least 350 different species of coral are found in the reef, which is 2,000 kilometers long and forms a natural breakwater for the east coast of Australia. Underlying sediments, twice as old as the reef itself, indicate that the region was once above sea level. Geological evidence shows that the reef began growing more than 25 million years ago. As the image shows, the “reef” is in fact composed of many individual detached reefs, separated by deep water channels. The calcareous remains of tiny creatures called coral polyps and hydrocorals provide the basic building material for the reefs while the remains of coraline algae and organisms called polyzoas provide the cement that holds the structure together. When fossilized, such reefs and the debris eroded from them form thick limestone units. The Great Barrier Reef is the largest reef on Earth at the present day. The reasons for its size and longevity are the very stablegeological setting of the Australian platform, and the favorable oceanic circulation. Coral cannot exist at temperatures below 21° centigrade. The warmth of the waters of the Australian continental shelf varies little with depth because of the stirring action of the southeast trade winds. These winds pound the outer edge of the reef for nine months of the year, and this also keeps the reef supplied with seawater rich in the organic material needed by the growing coral.
The Brandberg is an isolated massif reaching 2,606 meters, and rises much higher than any other feature for hundreds of kilometers around. It is composed of a single mass of granite that rose through the Earth’s crust some 120 million years ago. Slightly south and to the west of the Brandberg is the much-eroded Messum Intrusion. Both of these intrusions reflect a period of extraordinarily widespread geological unrest in the Earth’s history, which preceded the opening of the Atlantic Ocean and the effusion of vast volumes of basaltic lavas of the Karoo formation that form the Drakensberg plateau. Karoo lavas are exposed immediately to the west of the intrusion. Rocks forced aside by the upward movement of the intrusion are visible encircling the margin of the Brandberg, tilted sharply upward. Ancient gneisses, distinguished by their lineated texture, are conspicuous along the dry river valley in the center of the frame. The existence of a set of lavas in South America of the same age and type as those of the Karoo was used for many years by some geologists as strong evidence that Africa and South America had once been united. However, their arguments were not widely accepted until geophysical data demonstrated the reality of plate tectonics.
One of the most spectacular examples of anticlinal fold structures lie on the north shore of the Strait of Hormuz in the Persian Gulf. Located near the important city of Bandar Abbas, these folds form the foothills of the Zagros Mountains, which run north-northwesterly through Iran. The folds were formed when the Arabian shield collided with the western Asian continental mass about 4 to 10 million years ago. Subduction still continues slightly further east, beneath Baluchistan, but is inactive in the Gulf itself. Although not obvious in the photograph, the shortening expressed by the folds is accompanied by extensive thrusting on the easterly dipping planes. All the deformation is geologically young; the folded sediments are Paleogene and Neogene. Simple anticlinal structures are well know as classic traps for hydrocarbons, and some producing wells are located in the area. The other features that are prominent in this photograph are the dark circular patches. These represent the surface expression of salt domes that have risen diapirically from the Cambrian Hormuz salt horizon through the younger sediments to reach the surface. Only in a hot arid environment such as that of the Gulf can the soluble salt escape rapid erosion. Salt domes also are frequently favorable sites for trapping hydrocarbons.
The Republic of South Yemen lies on the edge of one of the world’s great sand seas, the Rubh-al-Khali, but even this dry desert region bears the unmistakable imprint of flowing streams and rivers. The branching pattern in the photograph could only have been produced by running water, draining off the surrounding land. These filigree patterns are termed “dendritic drainages” because of their similarity to the way in which trees branch out into progressively finer twigs. The term comes from the Greek dendrites, meaning tree-like. The dry gullies or waids appear to pose something of a paradox in an area that is apparently exceptionally arid desert, with no vestige of plant life. Freak rainstorms and flash flooding might deepen and extend the gullies, but they are far too infrequent at the present day to have produced the pattern seen here. The drainage pattern is clearly a fossil. When the Earth emerged from the last Ice Age, the Sahara and the Rubh-al-Khali were savanna grasslands with a more temperate climate and much higher rainfall than they experience today. Runoff from the coastal mountains carved the dendritic drainage pattern, which was then “fossilized” when the climate became more arid.
The Betsiboka is Madagascar’s main river, flowing for a total of 525 kilometers from north of Tananarive. The river is navigable for at least 130 kilometers inland and the lower reaches pictured here are noted for their extensive rice fields. While the red sediment being transported provides an attractive and informative example of a river estuary, it is a symptom of an ecological disaster for Madagascar. Humans have felled and cleared the island’s natural cover of tropical forest so extensively that soil erosion has been vastly accelerated. Much of the sediment visible in the river represents an irreplaceable natural asset. Brick-red lateritic soils, the result of tropical weathering, are responsible for the strong color of the sediments. Most of the deforestation in Madagascar has taken place over the last 20 years, the same period during which observations from space have been conducted. Recent observations show that very little of the original forest remains.
Prior to the opening of the Red Sea and the separation of Arabia and Africa, the site of the future ocean was marked by regional doming, rifting, and effusion of basaltic lavas. A thick pile of dissected basalt is visible in this photograph of the north coast of Somalia, which originally joined the south coast of Arabia. The lavas from a conspicuous, dark sequence with four or five topographic steps and their upper surface exhibits a prominent paleo-drainage pattern. An unconformity separates the basalts from the underlying Precambrian basement gneisses. The photograph also reveals the hot climate and harsh desert terrain of the Somali Republic. Nothing grows on the coastal strip where rain rarely falls. The land rises in steps to a highland plateau. At an elevation of 1,500 meters the climate is more pleasant than on the coast but, at a latitude only 10° from the equator, the sun is blistering and only scrub can survive.
What at first glance may look like swirls of paint on a blue canvas are in act the Belcher Islands in Hudson’s Bay. These unusual low-lying islands extend over about 13,000 square kilometers but have a land area of only about 2,800 square kilometers. Their ribbon-like appearance is the result of the submergence of an eroded sequence of thinly bedded, folded metasedimentary rocks, of which the harder, more resistant emerge above sea level. The rocks are of Aphebian age, 1.64 to 2.34 billion years old. The weight of the great continental ice sheets lying on northern Canada was sufficient to push the existing land below sea level by perhaps as much as 1,000 meters around Hudson’s Bay. Now that the ice has gone, the land is recovering isostatically, so the highest of the areas below sea level a few thousand years ago are now just emerging. The rate of uplift immediately after the Ice Age was about 12 centimeters per year; it has now slowed to 1 centimeter per year and this will continue for some time into the future. The rate of uplift may be slow enough that erosion is able to maintain the islands’ topography at a steady level.
The Andes mountains form one of the longest continuous mountain ranges on Earth, extending from the shores of the Caribbean as far south as the Magellan Straits. Perhaps the most surprising aspect of this range is how narrow it is over much of its length - the high part of the range is typically less than 150 kilometers broad. Illustrated is the section of the Andes near Coquimbo, Chile, where the highest peaks are 6,300 meters. Low lighting and the oblique perspective emphasize the narrowness of the range, which forms a formidable natural obstacle, and explains how the improbably long and thin country of Chile acquired its identity. In this part of the range, active volcanism is absent. The Benioff zone in this region has a very shallow dip (10°). To both north and south, the Benioff zone dips more steeply (30°) and volcanism is well developed. Clouds illuminated by the low sun hang over the Argentine Pampas beyond the Andes and illustrate the marked climatic differences between different sides of the Andes. In the south, the Chilean side of the Andes tends to be well watered and fertile, while the pampas are in rain shadow and tend to be very dry. Further north, the Chilean coast is exceptionally dry (and forms the Atacama desert) while the eastern slopes are much wetter.
Plankton find a rich feeding ground in the cold waters lying off the Namibian Desert coast. They have found a narrow corridor of cold, nutrient-rich water in the Benguela Current along the coast. Just a few kilometers out to sea, the warmer waters of the Atlantic do no support the plankton. The band of clouds across the top right of the frame has been created by the interaction of the colder waters of the current and the atmosphere, so the boundary between the cold coastal waters of the Benguela Current is clearly evident to the space observer. It is one of the subtle wonders of the fragile earthly environment that plankton, and the fish that feed on them, should find such attractive feeding grounds sandwiched between the Namibian desert, one of the driest places on earth, and the warm, nutrient-poor waters of the central Atlantic.
The Magellan spacecraft was the first planetary explorer to be launched by a space shuttle when it was carried aloft by the shuttle Atlantis from Kennedy Space Center in Florida on May 4, 1989. Atlantis took Magellan into low Earth orbit, where it was released from the shuttle’s cargo bay and fired by a solid-fuel motor called the Inertial Upper Stage (IUS) on its way to Venus. Magellan looped around the Sun one-and-a-half times before arriving at Venus on August 10, 1990. A solid-fuel motor on the spacecraft then fired, placing Magellan into a near-polar elliptical orbit around Venus.
On May 4, 1989, the Magellan spacecraft was deployed from the shuttle. The spacecraft is topped by a 3.7-meter diameter dish-shaped antenna that was a spare part left over from the Voyager program. The long, white, horn-shaped antenna, attached just to the left of the dish antenna, is the altimeter antenna that gathers data concerning the surface height of features on Venus. Most of the spacecraft is wrapped in reflective white thermal blankets that protect its sensitive instruments from solar radiation.
The Magellan spacecraft’s deployment from the shuttle Atlantis’ cargo bay was captured by an astronaut with a hand-held camera pointed through the shuttle’s aft flight deck windows. Deployment occurred in the early evening of May 4, 1989, after Atlantis had carried Magellan and its Inertial Upper Stage (IUS) booster rocket, into low Earth orbit. Once the shuttle was safely away from the spacecraft, the IUS ignited and placed Magellan on course for its 15-month journey to Venus.
On August 10, 1990, Magellan entered into orbit about Venus, as depicted in this artist’s view. During its 243-day primary mission, referred to as Cycle 1, the spacecraft mapped well over 80 percent of the planet with its high-resolution Synthetic Aperture Radar (SAR). The spacecraft returned more digital data in the first cycle than all previous U.S. planetary missions combined.
The sequence of events that comprise a Magellan mapping orbit are shown in this artist’s conception. For the first 37.2 minutes of each orbit, the Synthetic Aperture Radar measures and records a 20-kilometer wide swath of the planet’s surface. When Magellan reaches the high point of its orbit, the spacecraft turns its antenna toward Earth and transmits the data. After 113.8 minutes of transmitting, the antenna is repositioned for another orbit about Venus.