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104-618: Olympus Mons is the youngest of the large volcanoes on Mars, having formed during the Martian Hesperian Period with eruptions continuing well into the Amazonian Period . It has been known to astronomers since the late 19th century as the albedo feature Nix Olympica (Latin for "Olympic Snow"), and its mountainous nature was suspected well before space probes confirmed it as a mountain. Two impact craters on Olympus Mons have been assigned provisional names by

208-422: A central trough of molten, flowing lava. Partially collapsed lava tubes are visible as chains of pit craters, and broad lava fans formed by lava emerging from intact, subsurface tubes are also common. In places along the volcano's base, solidified lava flows can be seen spilling out into the surrounding plains, forming broad aprons, and burying the basal escarpment. Crater counts from high-resolution images taken by

312-462: A degree and order of 18 spherical harmonic solution produced. Further use of spatial a priori constraint method, which had taken the topography into account in solving the Kaula power law constraint, had favored model of up to degree 50 spherical harmonic solution in global resolution ( Goddard Mars Model-1 , or GMM-1) then the subsequent models with higher completeness and degree and order up to 120 for

416-463: A depth of about 32 km (105,000 ft) below the caldera floor. Crater size-frequency distributions on the caldera floors indicate the calderas range in age from 350 Mya to about 150 Mya. All probably formed within 100 million years of each other. It is possible that the magma chambers within Olympus Mons received new magma from the mantle after the caldera floors formed, leading to

520-477: A discrete stratum bound above or below by adjacent units (illustrated right). Using principles such as superpositioning (illustrated left), cross-cutting relationships , and the relationship of impact crater density to age, geologists can place the units into a relative age sequence from oldest to youngest. Units of similar age are grouped globally into larger, time-stratigraphic ( chronostratigraphic ) units, called systems . For Mars, four systems are defined:

624-497: A feature unique among the shield volcanoes of Mars, which may have been created by enormous flank landslides . Olympus Mons covers an area of about 300,000 km (120,000 sq mi), which is approximately the size of Italy or the Philippines , and it is supported by a 70 km (43 mi) thick lithosphere . The extraordinary size of Olympus Mons is likely because Mars lacks mobile tectonic plates . Unlike on Earth,

728-436: A geologic period represents the time interval over which the strata of a system were deposited, including any unknown amounts of time present in gaps. Periods are measured in years, determined by radioactive dating . On Mars, radiometric ages are not available except from Martian meteorites whose provenance and stratigraphic context are unknown. Instead, absolute ages on Mars are determined by impact crater density, which

832-603: A given system are apt to contain gaps ( unconformities ) analogous to missing pages from a book. In some places, rocks from the system are absent entirely due to nondeposition or later erosion. For example, rocks of the Cretaceous System are absent throughout much of the eastern central interior of the United States. However, the time interval of the Cretaceous (Cretaceous Period) still occurred there. Thus,

936-406: A map of crustal thickness were produced along with this model. Compared with MRO110C and other previous models, major improvement of the estimation of the gravity field comes from more careful modeling of the non-conservative forces applied to the spacecraft. [Surface resolution (km)] [¬600 km] [200–300 km] [~112 km] [~112 km] [115 km] The techniques in tracking

1040-429: A number of wrinkle ridges located at the basal escarpment. Why opposite sides of the mountain should show different styles of deformation may lie in how large shield volcanoes grow laterally and in how variations within the volcanic substrate have affected the mountain's final shape. Large shield volcanoes grow not only by adding material to their flanks as erupted lava, but also by spreading laterally at their bases. As

1144-407: A possibility cannot be ruled out. The two major tidal forces acting on Mars are the solar tide and Phobos tide. Love number k 2 is an important proportional dimensionless constant relating the tidal field acting to the body with the multipolar moment resulting from the mass distribution of the body. Usually k 2 can tell quadrupolar deformation. Finding k 2 is helpful in understanding

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1248-904: A rock outcrop in the Upper Ordovician Series of the Ordovician System. You could even collect a fossil trilobite there. However, you could not visit the Late Ordovician Epoch in the Ordovician Period and collect an actual trilobite. The Earth-based scheme of rigid stratigraphic nomenclature has been successfully applied to Mars for several decades now but has numerous flaws. The scheme will no doubt become refined or replaced as more and better data become available. (See mineralogical timeline below as example of alternative.) Obtaining radiometric ages on samples from identified surface units

1352-417: A volcano grows in size, the stress field underneath the volcano changes from compressional to extensional. A subterranean rift may develop at the base of the volcano, causing the underlying crust to spread apart. If the volcano rests on sediments containing mechanically weak layers (e.g., beds of water-saturated clay), detachment zones ( décollements ) may develop in the weak layers. The extensional stresses in

1456-532: Is 3.72076 m/s (about 38% of the gravity of Earth ) and it varies. In general, topography-controlled isostasy drives the short wavelength free-air gravity anomalies . At the same time, convective flow and finite strength of the mantle lead to long-wavelength planetary-scale free-air gravity anomalies over the entire planet. Variation in crustal thickness, magmatic and volcanic activities, impact-induced Moho -uplift, seasonal variation of polar ice caps, atmospheric mass variation and variation of porosity of

1560-674: Is a vast, low-lying plain that covers much of the northern hemisphere of Mars. It is generally interpreted to consist of reworked sediments originating from the Late Hesperian outflow channels and may be the remnant of an ocean that covered the northern lowland basins. Another interpretation of the Vastitas Borealis Formation is that it consists of lava flows. The Hesperian System is subdivided into two chronostratigraphic series : Lower Hesperian and Upper Hesperian. The series are based on referents or locations on

1664-479: Is about 600 km (370 mi) wide. Because the mountain is so large, with complex structure at its edges, allocating a height to it is difficult. Olympus Mons stands 21 km (13 mi) above the Mars global datum , and its local relief, from the foot of the cliffs which form its northwest margin to its peak, is over 21 km (13 mi) (a little over twice the height of Mauna Kea as measured from its base on

1768-485: Is an idealized stratigraphic column based on the physical rock record of a type area (type section) correlated with rocks sections from many different locations planetwide. A system is bound above and below by strata with distinctly different characteristics (on Earth, usually index fossils ) that indicate dramatic (often abrupt) changes in the dominant fauna or environmental conditions. (See Cretaceous–Paleogene boundary as example.) At any location, rock sections in

1872-422: Is assumed to be a static perfectly spherical body of radius R M , provided that there is only one satellite revolving around Mars in a circular orbit and such gravitation interaction is the only force acting in the system, the equation would be where G is the universal constant of gravitation (commonly taken as G = 6.674 × 10 m kg s ), M is the mass of Mars (most updated value: 6.41693 × 10 kg), m

1976-473: Is clearly necessary for a more complete understanding of Martian chronology. The Hesperian was a time of declining rates of impact cratering, intense and widespread volcanic activity, and catastrophic flooding. Many of the major tectonic features on Mars formed at this time. The weight of the immense Tharsis Bulge stressed the crust to produce a vast network of extensional fractures ( fossae ) and compressive deformational features ( wrinkle ridges ) throughout

2080-423: Is critical in maintaining hemispheric crustal variations and preventing channel flow. Combination studies on geophysics and geochemistry suggested that average crustal thickness could be down to 50 ± 12 km. Measurement of gravity field by different orbiters allows higher-resolution global Bouguer potential model to be produced. With local shallow density anomalies and effect of core flattening eliminated,

2184-623: Is done basically by the antennae of the Deep Space Network (DSN), with one-way, two-way and three-way Doppler and range tracking applied. One-way tracking means the data is transmitted in one way to the DSN from the spacecraft, while two-way and three-way involve transmitting signals from Earth to the spacecraft (uplink), and thereafter transponded coherently back to the Earth (downlink). The difference between two-way and three-way tracking is,

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2288-488: Is expansive and does not drop off in density with height as sharply as Earth's. The composition of Olympus Mons is approximately 44% silicates , 17.5% iron oxides (which give the planet its red coloration), 7% aluminium , 6% magnesium , 6% calcium , and particularly high proportions of sulfur dioxide with 7%. These results point to the surface being largely composed of basalts and other mafic rocks, which would have erupted as low viscosity lava flows and hence lead to

2392-582: Is heavily dependent upon models of crater formation over time. Accordingly, the beginning and end dates for Martian periods are uncertain, especially for the Hesperian/Amazonian boundary, which may be in error by a factor of 2 or 3. The lower boundary of the Hesperian System is defined as the base of the ridged plains, which are typified by Hesperia Planum and cover about a third of the planet's surface. In eastern Hesperia Planum,

2496-468: Is influenced more strongly by the denser mantle, and vice versa. However, it could also be contributed by the difference in density of the erupted volcanic load and sedimentary load, as well as subsurface intrusion and removal of material. Many of these anomalies are associated with either geological or topographic features. Few exception includes the 63°E, 71°N anomaly, which may represent an extensive buried structure as large as over 600 km, predated

2600-489: Is much more uncertain and could range anywhere from 3200 to 2000 Mya, with 3000 Mya being frequently cited. The Hesperian Period is roughly coincident with the Earth's early Archean Eon. With the decline of heavy impacts at the end of the Noachian, volcanism became the primary geologic process on Mars, producing vast plains of flood basalts and broad volcanic constructs ( highland paterae ). By Hesperian times, all of

2704-543: Is noted that older regions on Mars are isostatically compensated when the younger region are usually only partially compensated. Different volcanic constructs could behave differently in terms of gravity anomalies. Volcanoes Olympus Mons and the Tharsis Montes produce the smallest positive free-air gravity anomalies in the solar system. Alba Patera , also a volcanic rise, north of the Tharsis Montes , however, produces negative Bouguer anomaly, though its extension

2808-594: Is similar to that of Olympus Mons. And for the Elysium Mons , its center is found to have slight increase in Bouguer anomalies in an overall broad negative anomaly context in the Elysium rise. The knowledge of anomaly of volcanoes, along with density of the volcanic material, would be useful in determining the lithospheric composition and crustal evolution of different volcanic edifices. It has been suggested that

2912-542: Is sometimes written as J n {\displaystyle J_{n}} . The oldest technique in determining the gravity of Mars is through Earth-based observation. Later with the arrival of uncrewed spacecraft, subsequent gravity models were developed from radio tracking data. Before the arrival of the Mariner 9 and Viking orbiter spacecraft at Mars, only an estimate of the Mars gravitational constant GM, i.e.

3016-543: Is the Goddard Mars Model 3 (GMM-3), produced in 2016, with spherical harmonics solution up to degree and order 120. This model is developed from 16 years of radio tracking data from Mars Global Surveyor (MGS), Mars Odyssey and Mars Reconnaissance Orbiter (MRO), as well as the MOLA topography model and provides a global resolution of 115 km. A separate free-air gravity anomaly map, Bouguer gravity anomaly map and

3120-547: Is the Legendre polynomial of degree l {\displaystyle l} with m = 0 {\displaystyle m=0} and is the associated Legendre polynomial with m > 0 {\displaystyle m>0} . These are used to describe solutions of Laplace's equation . R {\displaystyle R} is the mean radius of the planet. The coefficient C ℓ 0 {\displaystyle C_{\ell 0}}

3224-790: Is the mass of the satellite, r is the distance between Mars and the satellite, and ω {\displaystyle \omega } is the angular velocity of the satellite, which is also equivalent to 2 π T {\displaystyle {\frac {2\pi }{T}}} ( T is the orbiting period of the satellite). Therefore, g = G M R M 2 = r 3 ω 2 R M 2 = 4 r 3 π 2 T 2 R M 2 {\displaystyle g={\frac {GM}{R_{M}^{2}}}={\frac {r^{3}\omega ^{2}}{R_{M}^{2}}}={\frac {4r^{3}\pi ^{2}}{T^{2}R_{M}^{2}}}} , where R M

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3328-508: Is the radius of Mars. With proper measurement, r , T , and R M are obtainable parameters from Earth. However, as Mars is a generic, non-spherical planetary body and influenced by complex geological processes, more accurately, the gravitational potential is described with spherical harmonic functions , following convention in geodesy; see Geopotential model . where r , ψ , λ {\displaystyle r,\psi ,\lambda } are spherical coordinates of

3432-429: Is too weak and needs more precise measurement on the perturbation of spacecraft in the future. No direct measurement of crustal thickness on Mars is currently available. Geochemical implications from SNC meteorites and orthopyroxenite meteorite ALH84001 suggested that mean crustal thickness of Mars is 100–250 km. Viscous relaxation analysis suggested that the maximum thickness is 50–100 km. Such thickness

3536-557: The International Astronomical Union : the 15.6-kilometre-diameter (9.7 mi) Karzok crater and the 10.4-kilometre-diameter (6.5 mi) Pangboche crater . They are two of several suspected source areas for shergottites , the most abundant class of Martian meteorites . As a shield volcano , Olympus Mons resembles the shape of the large volcanoes making up the Hawaiian Islands . The edifice

3640-517: The Laplacian plane etc., which allow calculation of the ratio of solar mass to the mass of Mars, moment of inertia and coefficient of the gravitational potential of Mars, and give initial estimates of the gravity field of Mars. Precise tracking of spacecraft is of prime importance for accurate gravity modeling, as gravity models are developed from observing tiny perturbation of spacecraft, i.e. small variation in velocity and altitude. The tracking

3744-584: The Mars Express orbiter in 2004 indicate that lava flows on the northwestern flank of Olympus Mons range in age from 115 million years old (Mya) to only 2 Mya. These ages are very recent in geological terms, suggesting that the mountain may still be volcanically active, though in a very quiescent and episodic fashion. The caldera complex at the peak of the volcano is made of at least six overlapping calderas and caldera segments (pictured). Calderas are formed by roof collapse following depletion and withdrawal of

3848-524: The Noachian (4000 million years ago) was 500 times higher than today. Planetary scientists still debate whether these high rates represent the tail end of planetary accretion or a late cataclysmic pulse that followed a more quiescent period of impact activity. Nevertheless, at the beginning of the Hesperian, the impact rate had probably declined to about 80 times greater than present rates, and by

3952-487: The Sun or Phobos can be measured by its gravity. This reveals how stiff the interior is, and shows that the core is partially liquid. The study of surface gravity of Mars can therefore yield information about different features and provide beneficial information for future Mars landings . To understand the gravity of Mars, its gravitational field strength g and gravitational potential U are often measured. Simply, if Mars

4056-430: The angular moment wheels . In addition, Martian precession and third body attraction due to the Sun , Moon and planets, which could affect the spacecraft orbit, as well as relavistic effects on the measurements should also be corrected. These factors could lead to offset of the true gravity field. Accurate modeling is thus required to eliminate the offset. Such work is still ongoing. Many researchers have outlined

4160-452: The convection current, which has been evolving with time. The correlation between certain topography anomalies and long-wavelength gravity anomalies, for example, the mid-Atlantic ridge and Carlsberg ridge , which are topography high and gravity high on the ocean floor, thus became the argument for the convection current idea on Earth in the 1970s, though such correlations are weak in the global picture. Another possible explanation for

4264-527: The crustal dichotomy of Mars. Almost all the crust thicker than 60 km are contributed by the southern highland, with generally uniform thickness. And the northern lowland in general has thinner crust. The crustal thickness of the Arabia Terra region and northern hemisphere are found to be latitude-dependent. The more southward towards the Sinai Planum and Lunae Planum , the more thickened

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4368-557: The lunar maria . These "ridged plains" are interpreted to be basaltic lava flows ( flood basalts ) that erupted from fissures. The number-density of large impact craters is moderate, with about 125–200 craters greater than 5 km in diameter per million km . Hesperian-aged ridged plains cover roughly 30% of the Martian surface; they are most prominent in Hesperia Planum, Syrtis Major Planum , Lunae Planum, Malea Planum, and

4472-418: The planet flattening and Tharsis bulge. Early study of the geoid in the 1950s and 1960s has focused on the low-degree harmonics of the Earth's gravity field in order to understand its interior structure. It has been suggested that such long-wavelength anomalies on Earth could be contributed by the sources located in deep mantle and not in the crust, for example, caused by the density differences in driving

4576-480: The universal constant of gravitation times the mass of Mars, was available for deducing the properties of the Martian gravity field. GM could be obtained through observations of the motions of the natural satellites of Mars ( Phobos and Deimos ) and spacecraft flybys of Mars ( Mariner 4 and Mariner 6 ). Long term Earth-based observations of the motions of Phobos and Deimos provide physical parameters including semi-major axis , eccentricity , inclination angle to

4680-404: The 19th century. The astronomer Patrick Moore pointed out that Schiaparelli (1835–1910) "had found that his Nodus Gordis and Olympic Snow [Nix Olympica] were almost the only features to be seen" during dust storms, and "guessed correctly that they must be high". The Mariner 9 spacecraft arrived in orbit around Mars in 1971 during a global dust-storm. The first objects to become visible as

4784-557: The Hesperian, Mars changed from the wetter and perhaps warmer world of the Noachian to the dry, cold, and dusty planet seen today. The absolute age of the Hesperian Period is uncertain. The beginning of the period followed the end of the Late Heavy Bombardment and probably corresponds to the start of the lunar Late Imbrian period, around 3700 million years ago ( Mya ). The end of the Hesperian Period

4888-400: The Martian geologic record. As originally conceived, the Hesperian System referred to the oldest surfaces on Mars that postdate the end of heavy bombardment . The Hesperian was thus a time period of rapidly declining impact cratering rates. However, the timing and rate of the decline are uncertain. The lunar cratering record suggests that the rate of impacts in the inner Solar System during

4992-569: The Pre-Noachian, Noachian , Hesperian, and Amazonian. Geologic units lying below (older than) the Noachian are informally designated Pre-Noachian. The geologic time ( geochronologic ) equivalent of the Hesperian System is the Hesperian Period. Rock or surface units of the Hesperian System were formed or deposited during the Hesperian Period. System and period are not interchangeable terms in formal stratigraphic nomenclature, although they are frequently confused in popular literature. A system

5096-479: The Syria-Solis-Sinai Plana in southern Tharsis . Martian time periods are based on geologic mapping of surface units from spacecraft images . A surface unit is a terrain with a distinct texture, color, albedo , spectral property, or set of landforms that distinguish it from other surface units and is large enough to be shown on a map. Mappers use a stratigraphic approach pioneered in

5200-457: The Tharsis rise, which presented a higher-friction zone at the volcano's base. Friction was higher in that direction because the sediments were thinner and probably consisted of coarser grained material resistant to sliding. The competent and rugged basement rocks of Tharsis acted as an additional source of friction. This inhibition of southeasterly basal spreading in Olympus Mons could account for

5304-459: The atmospheric pressure at the summit of Mount Everest is 32,000 pascals, or about 32% of Earth's sea level pressure. Even so, high-altitude orographic clouds frequently drift over the Olympus Mons summit, and airborne Martian dust is still present. Although the average Martian surface atmospheric pressure is less than one percent of Earth's, the much lower gravity of Mars increases the atmosphere's scale height ; in other words, Mars's atmosphere

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5408-412: The base of Olympus Mons and is thought to be due to the volcano's immense weight pressing down on the Martian crust. The depth of this depression is greater on the northwest side of the mountain than on the southeast side. Olympus Mons is partially surrounded by a region of distinctive grooved or corrugated terrain known as the Olympus Mons aureole. The aureole consists of several large lobes. Northwest of

5512-478: The beginning of the Late Hesperian the atmosphere had probably thinned to its present density. As the planet cooled, groundwater stored in the upper crust (mega regolith ) began to freeze, forming a thick cryosphere overlying a deeper zone of liquid water. Subsequent volcanic or tectonic activity occasionally fractured the cryosphere, releasing enormous quantities of deep groundwater to the surface and carving huge outflow channels . Much of this water flowed into

5616-401: The calculation, which may vary laterally on the planet and is affected by porosity and geochemistry of the rock. Relevant information could be obtained from Martian meteorites and in-situ analysis. Since Bouguer gravity anomalies have strong links with depth of crust-mantle boundary, one with positive Bouguer anomalies may mean that it has a thinner crust composed of lower density material and

5720-418: The correlation between short-wavelength (locally varying) free-air gravity anomalies and topography. For regions with higher correlation, free-air gravity anomalies could be expanded to higher degree strength through geophysical interpretation of surface features, so that the gravity map could offer higher resolution. It has been found that the southern highland has high gravity/topography correlation but not for

5824-478: The crust could also correlate to the lateral variations. Over the years models consisting of an increasing but limited number of spherical harmonics have been produced. Maps produced have included free-air gravity anomaly , Bouguer gravity anomaly , and crustal thickness. In some areas of Mars there is a correlation between gravity anomalies and topography. Given the known topography, higher resolution gravity field can be inferred. Tidal deformation of Mars by

5928-499: The crust is. Among all regions, the Thaumasia and Claritis contain the thickest portion of crust on Mars that account for the histogram > 70 km. The Hellas and Argyre basins are observed to have crust thinner than 30 km, which are the exceptionally thin area in the southern hemisphere. Isidis and Utopia are also observed to have significant crustal thinning, with the center of Isidis basins believed to have

6032-456: The crust of Mars remains fixed over a stationary hotspot , and a volcano can continue to discharge lava until it reaches an enormous height. Being a shield volcano, Olympus Mons has a very gently sloping profile. The average slope on the volcano's flanks is only 5%. Slopes are steepest near the middle part of the flanks and grow shallower toward the base, giving the flanks a concave upward profile. Its flanks are shallower and extend farther from

6136-406: The detachment zones can produce giant landslides and normal faults on the volcano's flanks, leading to the formation of a basal escarpment. Further from the volcano, these detachment zones can express themselves as a succession of overlapping, gravity driven thrust faults. This mechanism has long been cited as an explanation of the Olympus Mons aureole deposits (discussed below). Olympus Mons lies at

6240-443: The determination of even zonal, normalized gravity coefficient C l=2, m=0 , and odd zonal, normalized gravity coefficient C l=3, m=0 are crucial for outlining the time-variable gravity due to such mass exchange, where l {\displaystyle l} is the degree while m {\displaystyle m} is the order. More commonly, they are represented in form of C lm in research papers. If we regard

6344-409: The dust began to settle, the tops of the Tharsis volcanoes, demonstrated that the altitude of these features greatly exceeded that of any mountain found on Earth, as astronomers expected. Observations of the planet from Mariner 9 confirmed that Nix Olympica was a volcano. Ultimately, astronomers adopted the name Olympus Mons for the albedo feature known as Nix Olympica. Olympus Mons is located between

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6448-483: The early 1960s for photogeologic studies of the Moon . Although based on surface characteristics, a surface unit is not the surface itself or group of landforms . It is an inferred geologic unit (e.g., formation ) representing a sheetlike, wedgelike, or tabular body of rock that underlies the surface. A surface unit may be a crater ejecta deposit, lava flow, or any surface that can be represented in three dimensions as

6552-551: The early-Noachian buried surface. Strong correlation between topography and short-wavelength free-air gravity anomalies has been shown for both study of the gravity field of the Earth and the Moon, and it can be explained by the wide occurrence of isostasy. High correlation is expected for degree over 50 (short-wavelength anomaly) on Mars. And it could be as high as 0.9 for degrees between 70 and 85. Such correlation could be explained by flexural compensation of topographic loads. It

6656-708: The edge of the Tharsis bulge, an ancient vast volcanic plateau likely formed by the end of the Noachian Period . During the Hesperian , when Olympus Mons began to form, the volcano was located on a shallow slope that descended from the high in Tharsis into the northern lowland basins. Over time, these basins received large volumes of sediment eroded from Tharsis and the southern highlands. The sediments likely contained abundant Noachian-aged phyllosilicates (clays) formed during an early period on Mars when surface water

6760-420: The end of the Hesperian, some 700 million years later, the rate began to resemble that seen today. Gravity of Mars The gravity of Mars is a natural phenomenon, due to the law of gravity , or gravitation, by which all things with mass around the planet Mars are brought towards it. It is weaker than Earth's gravity due to the planet's smaller mass. The average gravitational acceleration on Mars

6864-508: The equation below, In turn, when there is more mass in the seasonal caps due to the more condensation of carbon dioxide from the atmosphere, the mass of the atmosphere would drop. They have inverse relationship with each other. And the change in mass has direct effect towards the measured gravitational potential. The seasonal mass exchange between the northern polar cap and southern polar cap exhibits long-wavelength gravity variation with time. Long years of continuous observation has found that

6968-457: The extruded lava could range from andesite (low density) to basaltic (high density) and the composition could change during the construction of the volcanic shield, which contributes to the anomaly. Another scenario is it is possible for high density material intruded beneath the volcano. Such setting has already been observed over the famous Syrtis major, which has been inferred to have an extinct magma chamber with 3300 kg m underlying

7072-448: The former one has the same signal transmitter and receiver on Earth, while the latter one has the transmitter and receiver at different locations on Earth. The use of these three types of tracking data enhances the coverage and quality of the data, as one could fill in the data gap of another. Doppler tracking is a common technique in tracking the spacecraft, utilizing radial velocity method, which involves detection of Doppler shifts. As

7176-444: The global scale anomalies is the finite strength of the mantle (in contrast to zero stress), which makes the gravity deviated from hydrostatic equilibrium . For this theory, because of the finite strength, flow may not exist for most of the region that are understressed. And the variations of density of the deep mantle could be the result of chemical inhomogeneities associated with continent separations, and scars left on Earth after

7280-559: The gravity-topography correlation in short-wavelength. However, not all regions on Mars show such correlation, notably the northern lowland and the poles. Misleading results could be easily produced, which could lead to wrong geophysics interpretation. The later modifications of gravity model include taking other non-conservative forces acting on spacecraft into account, including atmospheric drag , solar radiation pressure , Mars reflected solar radiation pressure , Mars thermal emission , and spacecraft thrusting which despins or desaturates

7384-448: The inflation of each chamber and uplift of parts of the volcano summit. Olympus Mons is structurally and topographically asymmetrical. The longer, more shallow northwestern flank displays extensional features, such as large slumps and normal faults . In contrast, the volcano's steeper southeastern side has features indicating compression, including step-like terraces in the volcano's mid-flank region (interpreted as thrust faults ) and

7488-422: The interior structure on Mars. The most updated k 2 obtained by Genova's team is 0.1697 ± 0.0009. As if k 2 is smaller than 0.10 a solid core would be indicated, this tells that at least the outer core is liquid on Mars, and the predicted core radius is 1520–1840 km. However, current radio tracking data from MGS, ODY and MRO does not allow the effect of phase lag on the tides to be detected because it

7592-472: The large shield volcanoes on Mars, including Olympus Mons , had begun to form. Volcanic outgassing released large amounts of sulfur dioxide (SO 2 ) and hydrogen sulfide (H 2 S) into the atmosphere, causing a transition in the style of weathering from dominantly phyllosilicate ( clay ) to sulfate mineralogy . Liquid water became more localized in extent and turned more acidic as it interacted with SO 2 and H 2 S to form sulfuric acid . By

7696-544: The latest GMM-3. Therefore, gravity models nowadays are not directly produced through transfer of the measured gravity data to any spatial information system because there is difficulty in producing model with sufficiently high resolution. Topography data obtained from the MOLA instrument aboard the Mars Global Surveyor thus becomes a useful tool in producing a more detailed short-scale gravity model, utilizing

7800-421: The low gradients on the surface of the planet. Olympus Mons is the result of many thousands of highly fluid, basaltic lava flows that poured from volcanic vents over a long period of time (the Hawaiian Islands exemplify similar shield volcanoes on a smaller scale – see Mauna Kea ). Like the basalt volcanoes on Earth, Martian basaltic volcanoes are capable of erupting enormous quantities of ash . Due to

7904-412: The low-degree harmonics of the gravity field, which cannot be attributed to local isostasy, but rather finite strength of the mantle and density differences in the convection current. For Mars, the largest component of Bouguer anomaly is the degree one harmonic, which represents the mass deficit in the southern hemisphere and excess in the northern hemisphere. The second largest component corresponds to

8008-538: The mass of ice stored in North Pole would increase by (1.4 ± 0.5) × 10 kg, while in South Pole it would decrease by (0.8 ± 0.6) × 10 kg. In addition, the atmosphere would have decrease in term of the mass of carbon dioxide by (0.6 ± 0.6) × 10 kg in long term as well. Due to existence of uncertainties, it is unclear whether migration of material from the South Pole to the North Pole is ongoing, though such

8112-639: The northern hemisphere where it probably pooled to form large transient lakes or an ice covered ocean. The Hesperian System and Period is named after Hesperia Planum , a moderately cratered highland region northeast of the Hellas basin. The type area of the Hesperian System is in the Mare Tyrrhenum quadrangle (MC-22) around 20°S 245°W  /  20°S 245°W  / -20; -245 . The region consists of rolling, wind-streaked plains with abundant wrinkle ridges resembling those on

8216-469: The northern lowland. Therefore, the resolution of free-air gravity anomaly model typically has higher resolution for the southern hemisphere, as high as over 100 km. Free-air gravity anomalies are relatively easier to measure than the Bouguer anomalies as long as topography data is available because it does not need to eliminate the gravitational effect due to the effect of mass surplus or deficit of

8320-424: The northwestern edge of the Tharsis region and the eastern edge of Amazonis Planitia . It stands about 1,200 km (750 mi) from the other three large Martian shield volcanoes, collectively called the Tharsis Montes ( Arsia Mons , Pavonis Mons , and Ascraeus Mons ). The Tharsis Montes are slightly smaller than Olympus Mons. A wide, annular depression or moat about 2 km (1.2 mi) deep surrounds

8424-535: The ocean floor). The total elevation change from the plains of Amazonis Planitia , over 1,000 km (620 mi) to the northwest, to the summit approaches 26 km (16 mi). The summit of the mountain has six nested calderas (collapsed craters) forming an irregular depression 60 km (37 mi) × 80 km (50 mi) across and up to 3.2 km (2.0 mi) deep. The volcano's outer edge consists of an escarpment , or cliff, up to 8 km (5.0 mi) tall (although obscured by lava flows in places),

8528-544: The planet where surface units indicate a distinctive geological episode, recognizable in time by cratering age and stratigraphic position. For example, Hesperia Planum is the referent location for the Lower Hesperian Series. The corresponding geologic time (geochronological) units of the two Hesperian series are the Early Hesperian and Late Hesperian Epochs . An epoch is a subdivision of a period;

8632-418: The reduced gravity of Mars compared to Earth, there are lesser buoyant forces on the magma rising out of the crust. In addition, the magma chambers are thought to be much larger and deeper than the ones found on Earth. The flanks of Olympus Mons are made up of innumerable lava flows and channels. Many of the flows have levees along their margins (pictured). The cooler, outer margins of the flow solidify, leaving

8736-711: The residual Bouguer potential is produced, as indicated by the following equation: The residual Bouguer potential is contributed by the mantle. The undulation of the crust-mantle boundary, or the Moho surface, with mass of terrain corrected, should have resulted in varying residual anomaly. In turn, if undulating boundary is observed, there should be changes in crustal thickness. Global study of residual Bouguer anomaly data indicates that crustal thickness of Mars varies from 5.8 km to 102 km. Two major peaks at 32 km and 58 km are identified from an equal-area histogram of crustal thickness. These two peaks are linked to

8840-422: The ridged plains overlie early to mid Noachian aged cratered plateau materials (pictured left). The Hesperian's upper boundary is more complex and has been redefined several times based on increasingly detailed geologic mapping. Currently, the stratigraphic boundary of the Hesperian with the younger Amazonian System is defined as the base of the Vastitas Borealis Formation (pictured right). The Vastitas Borealis

8944-574: The same time there are also some large basins that are not associated with such positive Bouguer anomaly, for example, Daedalia , northern Tharsis and Elysium , which are believed to be underlain by the northern lowland plain. In addition, certain portions of Coprates , Eos Chasma and Kasei Valles are also found to have positive Bouguer anomalies, though they are topographic depressions. This may suggest that these depressions are underlain by shallow dense intrusion body. Global gravity anomalies, also termed as long-wavelength gravity anomalies, are

9048-543: The spacecraft and geophysical interpretation of surface features can affect the resolution of the strength of gravity field. The better technique favors spherical harmonic solutions to higher degrees and orders. Independent analysis on Mariner 9 and Viking Orbiter tracking data yielded a degree and order of 6 spherical harmonic solution., Further combination of the two data sets, along with correlation of anomalies with volcanic features (positive anomaly) and deep-printed depression (negative anomaly) assisted by image data allows

9152-429: The spacecraft moves away from us along line of sight, there would be redshift of signal, while for the reverse, there would be blueshift of signal. Such technique has also been applied for observation of the motion of exoplanets. While for the range tracking, it is done through measurement of round trip propagation time of the signal. Combination of Doppler shift and range observation promotes higher tracking accuracy of

9256-552: The spacecraft. The tracking data would then be converted to develop global gravity models using the spherical harmonic equation displayed above. However, further elimination of the effects due to affect of solid tide , various relativistic effects due to the Sun, Jupiter and Saturn, non-conservative forces (e.g. angular momentum desaturations (AMD), atmospheric drag and solar radiation pressure ) have to be done, otherwise, considerable errors result. The latest gravity model for Mars

9360-512: The structural and topographic asymmetry of the mountain. Numerical models of particle dynamics involving lateral differences in friction along the base of Olympus Mons have been shown to reproduce the volcano's present shape and asymmetry fairly well. It has been speculated that the detachment along the weak layers was aided by the presence of high-pressure water in the sediment pore spaces, which would have interesting astrobiological implications. If water-saturated zones still exist in sediments under

9464-410: The subsurface magma chamber after an eruption. Each caldera thus represents a separate pulse of volcanic activity on the mountain. The largest and oldest caldera segment appears to have formed as a single, large lava lake. Using geometric relationships of caldera dimensions from laboratory models, scientists have estimated that the magma chamber associated with the largest caldera on Olympus Mons lies at

9568-410: The summit in the northwestern direction than they do to the southeast. The volcano's shape and profile have been likened to a "circus tent" held up by a single pole that is shifted off center. Due to the size and shallow slopes of Olympus Mons, an observer standing on the Martian surface would be unable to view the entire profile of the volcano, even from a great distance. The curvature of the planet and

9672-416: The terrain after the gravity is reduced to sea level. However, to interpret the crustal structure, further elimination of such gravitational effect is necessary so that the reduced gravity would only be the result of the core, mantle and crust below datum. The product after elimination is the Bouguer anomalies. However, density of the material in building up the terrain would be the most important constraint in

9776-565: The test point. λ {\displaystyle \lambda } is longitude and ψ {\displaystyle \psi } is latitude. C ℓ m {\displaystyle C_{\ell m}} and S ℓ m {\displaystyle S_{\ell m}} are dimensionless harmonic coefficients of degree l {\displaystyle l} and order m {\displaystyle m} . P ℓ m {\displaystyle P_{\ell }^{m}}

9880-541: The torn away of the moon. These are the cases suggested to work when slow flow is allowed to happen under certain circumstances. However, it has been argued that the theory may not be physically feasible. The sublimation - condensation cycle of carbon dioxide on Mars between the atmosphere and cryosphere (polar ice cap) operates seasonally. This cycle contributes as almost the only variable accounting for changes in gravity field on Mars. The measured gravitational potential of Mars from orbiters could be generalized as

9984-412: The two poles as two distinct point masses, then, their masses are defined as, Data has indicated that the maximum mass variation of the southern polar cap is approximately 8.4 × 10 kg, occurring near the autumnal equinox , while for that of the northern polar is approximately 6.2 × 10 kg, occurring in between the winter solstice and spring equinox . In long term speaking, it has been found that

10088-542: The two terms are not synonymous in formal stratigraphy. The age of the Early Hepserian/Late Hesperian boundary is uncertain, ranging from 3600 to 3200 million years ago based on crater counts. The average of the range is shown in the timeline below. Stratigraphic terms are typically confusing to geologists and non-geologists alike. One way to sort through the difficulty is by the following example: One could easily go to Cincinnati, Ohio and visit

10192-449: The volcano itself would obscure such a synoptic view. Similarly, an observer near the summit would be unaware of standing on a very high mountain, as the slope of the volcano would extend far beyond the horizon, a mere 3 kilometers away. The typical atmospheric pressure at the top of Olympus Mons is 72 pascals , about 12% of the average Martian surface pressure of 600 pascals. Both are exceedingly low by terrestrial standards; by comparison,

10296-507: The volcano, evident from positive Bouguer anomaly. Different depressions also behave differently in Bouguer anomaly. Giant impact basins like Argyre , Isidis , Hellas and Utopia basins also exhibit very strong positive Bouguer anomalies in circular manner. These basins have been debated for their impact crater origin. If they are, the positive anomalies may be due to uplift of Moho, crustal thinning and modification events by sedimentary and volcanic surface loads after impacting. But at

10400-414: The volcano, the aureole extends a distance of up to 750 km (470 mi) and is known as Lycus Sulci ( 24°36′N 219°00′E  /  24.600°N 219.000°E  / 24.600; 219.000 ). East of Olympus Mons, the aureole is partially covered by lava flows, but where it is exposed it goes by different names ( Gigas Sulci , for example). The origin of the aureole remains debated, but it

10504-418: The volcano, they would likely have been kept warm by a high geothermal gradient and residual heat from the volcano's magma chamber. Potential springs or seeps around the volcano would offer many possibilities for detecting microbial life. Olympus Mons and a few other volcanoes in the Tharsis region stand high enough to reach above the frequent Martian dust-storms recorded by telescopic observers as early as

10608-451: The western hemisphere. The huge equatorial canyon system of Valles Marineris formed during the Hesperian as a result of these stresses. Sulfuric-acid weathering at the surface produced an abundance of sulfate minerals that precipitated in evaporitic environments , which became widespread as the planet grew increasingly arid. The Hesperian Period was also a time when the earliest evidence of glacial activity and ice-related processes appears in

10712-415: Was abundant, and were thickest in the northwest where basin depth was greatest. As the volcano grew through lateral spreading, low-friction detachment zones preferentially developed in the thicker sediment layers to the northwest, creating the basal escarpment and widespread lobes of aureole material ( Lycus Sulci ). Spreading also occurred to the southeast; however, it was more constrained in that direction by

10816-448: Was likely formed by huge landslides or gravity-driven thrust sheets that sloughed off the edges of the Olympus Mons shield. Hesperian The Hesperian is a geologic system and time period on the planet Mars characterized by widespread volcanic activity and catastrophic flooding that carved immense outflow channels across the surface. The Hesperian is an intermediate and transitional period of Martian history. During

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