Mount Everest stands out at the center of the left image. Glaciers ... At 5,895 m, Mount Kilimanjaro is the highest point in Africa. Kilimanjaro is composed of three volcanoes, ...
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Kimberly J. Willis,
Patricia Wood Dickerson,
and Brett H. McRay
Office of Earth Sciences
NASA Johnson Space Center
Before heading towards Jupiter the Galileo spacecraft took these last images of the Earth and Moon in 1992. Although this image is a composite of two images, the scale is realistic. Please note that lunar and terrestrial features shown in this sequence are analogues in morphology but not necessarily in size or in mode of formation.
Apollo 15 astronauts Dave Scott (right) and Jim Irwin (left) received geology training along the rim of the Rio Grande Gorge. The landing site for Apollo 15 was Hadley Rille located along the rim of Mare Imbrium. The Rio Grande Gorge was considered the closest terrestrial analogue to Hadley since both were over 100 km wide, greater than 1 km in width and over 200 m deep. On the moon Jim Irwin is seen digging a trench to sample lunar regolith.
Layered igneous bedrock is visible along the upper 60 m of Hadley Rille (left) which is believed to be a collapsed lava tube or channel about 3.3 billion years (b.y.) in age. Because of its similar dimensions and bedrock, the Rio Grande Gorge, New Mexico, was chosen as the training site for Apollo 15 astronauts. The steep-walled canyon (right) exposes a cross section of a volcano-covered plateau; the Servilleta basalt is nearly identical to basalts of the ocean floor (3.6 to 4.5 million years old).
Grabens, downdropped blocks between parallel faults, develop where planetary crust is stretched. The Dead Sea (NW view - left) lies in a fault valley that is forming as the Arabian tectonic plate pulls away from the African plate in response to Red Sea rifting. Most lunar grabens are found at edges of mare basins and were caused by extensional forces created when the basins filled with lava (~3 b.y. ago). Increasing weight in basins creates tension along the margins, followed by faulting and foundering of grabens.
The Sudbury structure is one of North America’s oldest and largest impacts. The original size of the structure has been estimated at 220 km and the age at 1.85 b.y. Regional tectonism has distorted the crater into an ellipse, the center of which is a 27 X 59 km basin that contains predominantly nickel ore. The origin of this ore body is disputed. The leading theory is that the ore body is the result of an impact that melted upper and lower crustal material. A similar theory of an impact creating volcanism was proposed for the Moon. In contrast, it is now believed that the filling of impact basins (3.8 to possibly as recently as 1.5 b.y.) came long after the basins themselves were formed (~3.85 b.y.). Mare Moscoviense is located on the lunar far side and is 221 km in diameter.
Although the scale may vary, craters on different planetary bodies share similar characteristics. Manicouagan crater in Quebec, Canada, and Copernicus crater on the Moon are both complex craters. Terraced walls and a central peak are exhibited by the 93 km diameter Copernicus crater. Manicouagan (100 km diameter) is an eroded crater where a resistant melt sheet is surrounded by a 70 km frozen reservoir. The difference in erosion rates is readily apparent by the youthful looking, <1 b.y. old Copernicus crater as compared to a younger, 212 m.y. Manicouagan.
This simple crater in Arizona has been called Arizona crater, Barringer crater, and Meteor crater. Both lunar and terrestrial simple craters share the same bowl shape. Meteor crater was formed 50,000 years ago by the impact of a 100,000-ton iron meteorite resulting, in the 1.2-km-diameter crater visible today. The simple lunar crater (right) is Isidorus D, is 15 km in diameter and is located in the lunar highlands.
Mars is about half the size of Earth and lacks oceans, but on the Martian surface are features analogous to those on Earth: polar caps, volcanoes, canyons, impact craters, dunes, drainage channels, clouds, dust storms. Please note that features shown in this sequence are analogues in morphology but not necessarily in size or mode of formation.
The heavily cratered terrain on Mars resembles the highlands of the Moon. The densely cratered southern hemisphere indicates an older age, possibly as old as 4 b.y. as compared to other regions, i.e., Valles Marineris, Olympus Mons, etc. The larger craters, >20 km in diameter are shallower, with flatter floors and more limited rim deposits than similar sized lunar craters. The Earth has a younger surface than Mars, thanks to plate tectonics. Terrestrial impact craters (left), such as Gosses Bluff (central Australia) are more eroded than are the Martian counterparts.
Details of Gosses Bluff impact crater in the orange semi-desert of Australia and Arandes on Mars. Gosses Bluff crater is 22 km in diameter and about 142 m.y. old; the eroded remnant of the 5-km inner peak ring is visible (arrow). On the right is the 28-km-diameter Martian crater Arandes. A central peak can be seen at the center of the crater.
Volcanoes of the Tibesti Massif (left) in Chad, the highest point in the Sahara, are believed to arise from a hot spot under the African continent. Emi Koussi is the southernmost volcano in this SW-looking view. While most circular features in Tibesti are volcanoes, there is one exception, the Aorounga impact crater in the windstreaks southeast of Emi Koussi volcano.
Volcanoes on Mars tend to be larger than their terrestrial counterparts. Elysium Mons (left) is on the Elysium Bulge southwest of Olympus Mons. This shield volcano rises 9 km above the surrounding plains and the summit caldera is ~15 km in diameter. Emi Koussi is one of several volcanoes on the Tibesti Massif in Chad, Emi Koussi is a Holocene stratovolcano ~101 km wide and 2.3 km high. The summit caldera is 19 km wide.
The Okavango River in Botswana, Africa empties into no sea or ocean, instead it flows into a broad shallow graben. The dark patches on the delta are swamps, the parallel linear features are stabilized sand dunes. The Martian valley network on the right is in the southern hemisphere within the cratered terrain. The Mars image is 200 km across.
Sand dunes are common in some regions on Earth and Mars. In Saudi Arabia dunes form in the lowlands of the Saudi Arabian peninsula. One of the major dune fields is An Nafud in northern Saudi. Two major dune types predominate. Barchan dunes are crescent shaped and the tips of the crescent point downwind. Transverse dunes are linear and perpendicular to the wind direction. This kind of dune forms where winds are strong and sand is abundant. Dunes in the An Nafud field can reach heights of 90m. Barchan and transverse dunes are also visible in the Mars image.
Small barchan dunes (left image - horizontal linear features below and next to Sandwich Bay) occur in the northern section of the Namib Sand Sea. Terrestrial barchan dunes indicate a unidirectional wind source. The long features from the lower right to upper center are linear dunes. On the right is a Mars Global Surveyor image of barchan dunes located near the north polar cap (74.7°N, 61.4°W). The light color of the dunes is due to a covering of frost.
The vast canyonlands of the Colorado Plateau and Mars share great valleys and similarly colored landscapes. As on Mars, the reds and pinks of this terrestrial region are caused by oxidation of tiny iron particles. Uplift in Utah ~10 million years ago caused the Colorado River to cut canyons deep into the plateau. The origin of Valles Marineris is thought to be related to the rise of the Tharsis Bulge to the west. This uplift stressed and fractured the Martian crust, creating the 7 to 10-km-deep valley. The Mars image on the right is approximately 475 km across.
Earth’s closest analogue to Valles Marineris is the Grand Canyon. Even though Mars is about half the size of Earth, Valles Marineris is about 4 times deeper, 20 times wider, and 10 times longer than the Grand Canyon. At 4,000 km long, Valles Marineris would almost span the distance from the west coast to the east coast of the United States. The image on the right is 60 km across.
Mount Everest stands out at the center of the left image. Glaciers flow from the high Tibetan Himalayas. At 8,850 m the summit of Everest is the highest point on Earth that is entirely above sea level. In the Nilosyrtis area (34N, 290W) the ridges and grooves in the valley are suggestive of glacial flow. The right image is approximately 35 km across.
The Island of Hawaii is often used as an analogue to Olympus Mons as both are large shield volcanoes. Scale is where the similarity ends. If the subsea volcanic edifice is considered as well as that above sea level, the elevation of Hawaii is 9 km. Olympus Mons is the highest volcano in the Solar System at 27 km above the surrounding plains, making it 3 times higher than Mount Everest.
Five volcanoes make up the Island of Hawaii, Mauna Loa, Mauna Kea, Kilauea, Kohala, and Hualalai. Although the appearance of the summit calderas for Mauna Loa and Olympus Mons are similar there is a great difference in scale. The caldera of Olympus Mons is 80 km while that of Mauna Loa is 5 km X 3.2 km in diameter.
At 5,895 m, Mount Kilimanjaro is the highest point in Africa. Kilimanjaro is composed of three volcanoes, Kibo, Mawensi, and Shira. The highest peak is capped by a glacier. Ascreus Mons is one of three volcanoes in the Tharsis Bulge, situated between Olympus Mons (west) and Valles Marineris (east). Ascreus is a giant shield volcano that may have been capped by a glacier under earlier Martian climatic conditions.
At 20 km wide, Byrd Glacier is the largest glacier in the Transantarctic Mountains. It is also one of the fastest moving glaciers in Antarctica, advancing several hundred meters per year. The Mars image is of layered terrain in the north polar area. The polar caps on Mars are made up primarily of frozen CO2 and are much thinner than are polar caps on Earth. Small amounts of water ice are present in the Martian polar caps.
Man must rise above the Earth --
to the top of the atmosphere and beyond --
only thus will he fully understand the world in which he lives.
Socrates, 500 B.C.
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Canyons, Craters and Drifting Dunes -
Terrestrial Analogues and Earth’s Moon and Mars
Kimberly Willis, Patricia Wood Dickerson and Brett McRay
NASA -- Johnson Space Center
OFFICE OF EARTH SCIENCES -- Kamlesh Lulla, Chief