120-509: Andrew S. Long (born 1965) is an Australian geophysicist . He has a PhD in geophysics (1996) from the University of Western Australia , and a post-doctoral term at Stanford University . He is a leader in the application of geophysical technologies to exploration for oil and gas in marine areas, and has written and presented several papers at the Society of Exploration Geophysicists (SEG),
240-526: A lunar eclipse , always illuminated by the Sun, but from Earth the visible illumination shifts during its orbit, producing the lunar phases . The Moon is the brightest celestial object in Earth's night sky . This is mainly due to its large angular diameter , while the reflectance of the lunar surface is comparable to that of asphalt . The apparent size is nearly the same as that of the Sun, allowing it to cover
360-608: A broader definition that includes the water cycle including snow and ice; fluid dynamics of the oceans and the atmosphere ; electricity and magnetism in the ionosphere and magnetosphere and solar-terrestrial physics ; and analogous problems associated with the Moon and other planets. Although geophysics was only recognized as a separate discipline in the 19th century, its origins date back to ancient times. The first magnetic compasses were made from lodestones , while more modern magnetic compasses played an important role in
480-477: A bronze ball from the mouth of a dragon into the mouth of a toad. By looking at which of eight toads had the ball, one could determine the direction of the earthquake. It was 1571 years before the first design for a seismoscope was published in Europe, by Jean de la Hautefeuille . It was never built. The 17th century had major milestones that marked the beginning of modern science. In 1600, William Gilbert release
600-406: A compass in Europe was in 1190 AD. In circa 240 BC, Eratosthenes of Cyrene deduced that the Earth was round and measured the circumference of Earth with great precision. He developed a system of latitude and longitude . Perhaps the earliest contribution to seismology was the invention of a seismoscope by the prolific inventor Zhang Heng in 132 AD. This instrument was designed to drop
720-425: A decisive role on local surface temperatures . Parts of many craters, particularly the bottoms of many polar craters, are permanently shadowed, these " craters of eternal darkness " have extremely low temperatures. The Lunar Reconnaissance Orbiter measured the lowest summer temperatures in craters at the southern pole at 35 K (−238 °C; −397 °F) and just 26 K (−247 °C; −413 °F) close to
840-434: A few kilometers wide), shallower, and more irregularly shaped than impact craters. They also lack the upturned rims characteristic of impact craters. Several geologic provinces containing shield volcanoes and volcanic domes are found within the near side maria. There are also some regions of pyroclastic deposits , scoria cones and non-basaltic domes made of particularly high viscosity lava. Almost all maria are on
960-503: A global dipolar magnetic field and only has crustal magnetization likely acquired early in its history when a dynamo was still operating. Early in its history, 4 billion years ago, its magnetic field strength was likely close to that of Earth today. This early dynamo field apparently expired by about one billion years ago, after the lunar core had crystallized. Theoretically, some of the remnant magnetization may originate from transient magnetic fields generated during large impacts through
1080-718: A hospitable environment for future astronauts, protecting them from extreme temperatures, solar radiation, and micrometeorites. However, challenges include accessibility and risks of avalanches and cave-ins. This discovery offers potential for future lunar bases or emergency shelters. The main features visible from Earth by the naked eye are dark and relatively featureless lunar plains called maria (singular mare ; Latin for "seas", as they were once believed to be filled with water) are vast solidified pools of ancient basaltic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water. The majority of these lava deposits erupted or flowed into
1200-533: A landscape featuring craters of all ages. The Moon was volcanically active until 1.2 billion years ago, which laid down the prominent lunar maria . Most of the mare basalts erupted during the Imbrian period , 3.3–3.7 billion years ago, though some are as young as 1.2 billion years and some as old as 4.2 billion years. There are differing explanations for the eruption of mare basalts, particularly their uneven occurrence which mainly appear on
1320-665: A lesser extent, the Sun 's—are the main drivers of Earth's tides . In geophysical terms , the Moon is a planetary-mass object or satellite planet . Its mass is 1.2% that of the Earth, and its diameter is 3,474 km (2,159 mi), roughly one-quarter of Earth's (about as wide as the United States from coast to coast ). Within the Solar System , it is the largest and most massive satellite in relation to its parent planet ,
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#17327918778361440-426: A magnetosphere. Early space probes mapped out the gross dimensions of the Earth's magnetic field, which extends about 10 Earth radii towards the Sun. The solar wind, a stream of charged particles, streams out and around the terrestrial magnetic field, and continues behind the magnetic tail , hundreds of Earth radii downstream. Inside the magnetosphere, there are relatively dense regions of solar wind particles called
1560-663: A million years or so, the polarity of the Earth's field reverses. These geomagnetic reversals , analyzed within a Geomagnetic Polarity Time Scale , contain 184 polarity intervals in the last 83 million years, with change in frequency over time, with the most recent brief complete reversal of the Laschamp event occurring 41,000 years ago during the last glacial period . Geologists observed geomagnetic reversal recorded in volcanic rocks, through magnetostratigraphy correlation (see natural remanent magnetization ) and their signature can be seen as parallel linear magnetic anomaly stripes on
1680-435: A publication titled De Magnete (1600) where he conducted series of experiments on both natural magnets (called 'loadstones ') and artificially magnetized iron. His experiments lead to observations involving a small compass needle ( versorium ) which replicated magnetic behaviours when subjected to a spherical magnet, along with it experiencing ' magnetic dips ' when it was pivoted on a horizontal axis. HIs findings led to
1800-428: A radius of about 500 kilometres (310 mi). This structure is thought to have developed through the fractional crystallization of a global magma ocean shortly after the Moon's formation 4.5 billion years ago. Crystallization of this magma ocean would have created a mafic mantle from the precipitation and sinking of the minerals olivine , clinopyroxene , and orthopyroxene ; after about three-quarters of
1920-458: A satellite with similar mass and iron content to the Moon into orbit far outside Earth's Roche limit . Even satellites that initially pass within the Roche limit can reliably and predictably survive, by being partially stripped and then torqued onto wider, stable orbits. On November 1, 2023, scientists reported that, according to computer simulations, remnants of Theia could still be present inside
2040-475: A study of Ina , a tiny depression in Lacus Felicitatis , found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old. Moonquakes and releases of gas indicate continued lunar activity. Evidence of recent lunar volcanism has been identified at 70 irregular mare patches , some less than 50 million years old. This raises
2160-502: A texture resembling snow and a scent resembling spent gunpowder . The regolith of older surfaces is generally thicker than for younger surfaces: it varies in thickness from 10–15 m (33–49 ft) in the highlands and 4–5 m (13–16 ft) in the maria. Beneath the finely comminuted regolith layer is the megaregolith , a layer of highly fractured bedrock many kilometers thick. These extreme conditions are considered to make it unlikely for spacecraft to harbor bacterial spores at
2280-439: A trans-Atlantic flight, 200 times more than on Earth's surface. For further comparison radiation on a flight to Mars is about 1.84 millisieverts per day and on Mars on average 0.64 millisieverts per day, with some locations on Mars possibly having levels as low as 0.342 millisieverts per day. The Moon's axial tilt with respect to the ecliptic is only 1.5427°, much less than the 23.44° of Earth. Because of this small tilt,
2400-410: Is Earth 's only natural satellite . It orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Earth. Tidal forces between Earth and the Moon have synchronized the Moon's orbital period ( lunar month ) with its rotation period ( lunar day ) at 29.5 Earth days, causing the same side of the Moon to always face Earth. The Moon's gravitational pull—and, to
2520-451: Is a gap of 12 hours and 25 minutes between every high tide and between every low tide. Gravitational forces make rocks press down on deeper rocks, increasing their density as the depth increases. Measurements of gravitational acceleration and gravitational potential at the Earth's surface and above it can be used to look for mineral deposits (see gravity anomaly and gravimetry ). The surface gravitational field provides information on
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#17327918778362640-538: Is a very complex substance and its unique properties are essential for life. Its physical properties shape the hydrosphere and are an essential part of the water cycle and climate . Its thermodynamic properties determine evaporation and the thermal gradient in the atmosphere . The many types of precipitation involve a complex mixture of processes such as coalescence , supercooling and supersaturation . Some precipitated water becomes groundwater , and groundwater flow includes phenomena such as percolation , while
2760-503: Is about 4.2 × 10 W , and it is a potential source of geothermal energy. Seismic waves are vibrations that travel through the Earth's interior or along its surface. The entire Earth can also oscillate in forms that are called normal modes or free oscillations of the Earth . Ground motions from waves or normal modes are measured using seismographs . If the waves come from a localized source such as an earthquake or explosion, measurements at more than one location can be used to locate
2880-440: Is always a downward electric field near the surface that averages 120 volts per meter. Relative to the solid Earth, the ionization of the planet's atmosphere is a result of the galactic cosmic rays penetrating it, which leaves it with a net positive charge. A current of about 1800 amperes flows in the global circuit. It flows downward from the ionosphere over most of the Earth and back upwards through thunderstorms. The flow
3000-489: Is around 3 × 10 atm (0.3 nPa ); it varies with the lunar day. Its sources include outgassing and sputtering , a product of the bombardment of lunar soil by solar wind ions. Elements that have been detected include sodium and potassium , produced by sputtering (also found in the atmospheres of Mercury and Io ); helium-4 and neon from the solar wind; and argon-40 , radon-222 , and polonium-210 , outgassed after their creation by radioactive decay within
3120-532: Is asymmetric, being more dense near the boundary between the Moon's dayside and nightside. Ionizing radiation from cosmic rays , the Sun and the resulting neutron radiation produce radiation levels on average of 1.369 millisieverts per day during lunar daytime , which is about 2.6 times more than on the International Space Station with 0.53 millisieverts per day at about 400 km above Earth in orbit, 5–10 times more than during
3240-526: Is believed to be caused by high-energy electrons that get caught in the Van Allen radiation belt . Whistlers are produced by lightning strikes. Hiss may be generated by both. Electromagnetic waves may also be generated by earthquakes (see seismo-electromagnetics ). In the highly conductive liquid iron of the outer core, magnetic fields are generated by electric currents through electromagnetic induction. Alfvén waves are magnetohydrodynamic waves in
3360-551: Is concerned with the shape of the Earth, and by extension the mapping of features around and in the planet, geophysical measurements include high accuracy GPS measurements. These measurements are processed to increase their accuracy through differential GPS processing. Once the geophysical measurements have been processed and inverted, the interpreted results are plotted using GIS. Programs such as ArcGIS and Geosoft were built to meet these needs and include many geophysical functions that are built-in, such as upward continuation , and
3480-468: Is divided into the upper mantle , transition zone, lower mantle and D′′ layer. Between the crust and the mantle is the Mohorovičić discontinuity . The seismic model of the Earth does not by itself determine the composition of the layers. For a complete model of the Earth, mineral physics is needed to interpret seismic velocities in terms of composition. The mineral properties are temperature-dependent, so
3600-561: Is estimated from about 500 km (300 miles) to 1,737 km (1,079 miles). While the giant-impact theory explains many lines of evidence, some questions are still unresolved, most of which involve the Moon's composition. Models that have the Moon acquiring a significant amount of the proto-earth are more difficult to reconcile with geochemical data for the isotopes of zirconium, oxygen, silicon, and other elements. A study published in 2022, using high-resolution simulations (up to 10 particles), found that giant impacts can immediately place
3720-459: Is liquid, and the motion of this highly conductive fluid generates the Earth's field. Earth's inner core , however, is solid because of the enormous pressure. Reconstruction of seismic reflections in the deep interior indicates some major discontinuities in seismic velocities that demarcate the major zones of the Earth: inner core , outer core , mantle, lithosphere and crust . The mantle itself
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3840-410: Is mainly composed of silicates , and the boundaries between layers of the mantle are consistent with phase transitions. The mantle acts as a solid for seismic waves, but under high pressures and temperatures, it deforms so that over millions of years it acts like a liquid. This makes plate tectonics possible. If a planet's magnetic field is strong enough, its interaction with the solar wind forms
3960-466: Is manifested by lightning below the clouds and sprites above. A variety of electric methods are used in geophysical survey. Some measure spontaneous potential , a potential that arises in the ground because of human-made or natural disturbances. Telluric currents flow in Earth and the oceans. They have two causes: electromagnetic induction by the time-varying, external-origin geomagnetic field and motion of conducting bodies (such as seawater) across
4080-440: Is on average about 1.9 km (1.2 mi) higher than that of the near side. The discovery of fault scarp cliffs suggest that the Moon has shrunk by about 90 metres (300 ft) within the past billion years. Similar shrinkage features exist on Mercury . Mare Frigoris, a basin near the north pole long assumed to be geologically dead, has cracked and shifted. Since the Moon does not have tectonic plates, its tectonic activity
4200-477: Is simply Moon , with a capital M. The noun moon is derived from Old English mōna , which (like all its Germanic cognates) stems from Proto-Germanic *mēnōn , which in turn comes from Proto-Indo-European *mēnsis 'month' (from earlier *mēnōt , genitive *mēneses ) which may be related to the verb 'measure' (of time). Occasionally, the name Luna / ˈ l uː n ə / is used in scientific writing and especially in science fiction to distinguish
4320-574: Is slow and cracks develop as it loses heat. Scientists have confirmed the presence of a cave on the Moon near the Sea of Tranquillity , not far from the 1969 Apollo 11 landing site. The cave, identified as an entry point to a collapsed lava tube, is roughly 45 meters wide and up to 80 m long. This discovery marks the first confirmed entry point to a lunar cave. The analysis was based on photos taken in 2010 by NASA's Lunar Reconnaissance Orbiter . The cave's stable temperature of around 17 °C could provide
4440-476: Is the lowest point on the surface of the Moon. The highest elevations of the Moon's surface are located directly to the northeast, which might have been thickened by the oblique formation impact of the South Pole–Aitken basin. Other large impact basins such as Imbrium , Serenitatis , Crisium , Smythii , and Orientale possess regionally low elevations and elevated rims. The far side of the lunar surface
4560-484: The Adams–Williamson equation . The conclusion is that pressure alone cannot account for the increase in density. Instead, we know that the Earth's core is composed of an alloy of iron and other minerals. Reconstructions of seismic waves in the deep interior of the Earth show that there are no S-waves in the outer core. This indicates that the outer core is liquid, because liquids cannot support shear. The outer core
4680-564: The Earth sciences at the graduate level, complete investigations across a wide range of scientific disciplines. The term geophysics classically refers to solid earth applications: Earth's shape ; its gravitational , magnetic fields , and electromagnetic fields ; its internal structure and composition ; its dynamics and their surface expression in plate tectonics , the generation of magmas , volcanism and rock formation. However, modern geophysics organizations and pure scientists use
4800-878: The European Association of Geoscientists and Engineers (EAGE), the Australian Society of Exploration Geophysicists (ASEG), the Australian Petroleum Production & Exploration Association (APPEA) and many other international conventions and journals. Awards include the 1992 Alumni Medal award for outstanding post-graduate from Curtin University of Technology , ASEG Best Presentation (1994), ASEG Best Paper (2004), Indonesian Petroleum Association (IPA) Best Paper Professional for Geophysics and Formation Evaluation (2009) and APPEA Best Oral Presentation (2014). Early leader in
4920-539: The International Union of Geodesy and Geophysics encompass both. Absolute positions are most frequently determined using the global positioning system (GPS). A three-dimensional position is calculated using messages from four or more visible satellites and referred to the 1980 Geodetic Reference System . An alternative, optical astronomy , combines astronomical coordinates and the local gravity vector to get geodetic coordinates. This method only provides
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5040-405: The conductivity of water makes electrical and electromagnetic methods useful for tracking groundwater flow. Physical properties of water such as salinity have a large effect on its motion in the oceans. The many phases of ice form the cryosphere and come in forms like ice sheets , glaciers , sea ice , freshwater ice, snow, and frozen ground (or permafrost ). Contrary to popular belief,
5160-443: The elastic properties of minerals; their high-pressure phase diagrams , melting points and equations of state at high pressure; and the rheological properties of rocks, or their ability to flow. Deformation of rocks by creep make flow possible, although over short times the rocks are brittle. The viscosity of rocks is affected by temperature and pressure, and in turn, determines the rates at which tectonic plates move. Water
5280-442: The geotherm must also be determined. This requires physical theory for thermal conduction and convection and the heat contribution of radioactive elements . The main model for the radial structure of the interior of the Earth is the preliminary reference Earth model (PREM). Some parts of this model have been updated by recent findings in mineral physics (see post-perovskite ) and supplemented by seismic tomography . The mantle
5400-465: The magnetosphere or the Earth's core. In the core, they probably have little observable effect on the Earth's magnetic field, but slower waves such as magnetic Rossby waves may be one source of geomagnetic secular variation . Electromagnetic methods that are used for geophysical survey include transient electromagnetics , magnetotellurics , surface nuclear magnetic resonance and electromagnetic seabed logging. The Earth's magnetic field protects
5520-462: The precession of the equinox (the orbit of whole star patterns along an ecliptic axis . Newton's theory of gravity had gained so much success, that it resulted in changing the main objective of physics in that era to unravel natures fundamental forces, and their characterizations in laws. The first seismometer , an instrument capable of keeping a continuous record of seismic activity, was built by James Forbes in 1844. Moon The Moon
5640-639: The EAGE and SEG. Versions of the 2009 Multi-Level Source paper were awarded Best Presentation awards at the Indonesian Petroleum Association (IPA) and SEG annual meetings, and the paper titled Low Frequency Seismic: The Next Revolution in Resolution was awarded Best Presentation at the 2014 annual APPEA meeting. In 2009 he was honoured as the inaugural Honorary Lecturer for Pacific South for the Society of Exploration Geophysicists ,
5760-411: The Earth and its surroundings. Geophysicists also investigate the physical processes and properties of the Earth, its fluid layers, and magnetic field along with the near-Earth environment in the Solar System , which includes other planetary bodies. The gravitational pull of the Moon and Sun gives rise to two high tides and two low tides every lunar day, or every 24 hours and 50 minutes. Therefore, there
5880-452: The Earth and the material accreted and formed the Moon just beyond the Earth's Roche limit of ~ 2.56 R 🜨 . Giant impacts are thought to have been common in the early Solar System. Computer simulations of giant impacts have produced results that are consistent with the mass of the lunar core and the angular momentum of the Earth–Moon system. These simulations show that most of
6000-447: The Earth from the deadly solar wind and has long been used for navigation. It originates in the fluid motions of the outer core. The magnetic field in the upper atmosphere gives rise to the auroras . The Earth's field is roughly like a tilted dipole , but it changes over time (a phenomenon called geomagnetic secular variation). Mostly the geomagnetic pole stays near the geographic pole , but at random intervals averaging 440,000 to
6120-599: The Earth rotates, as the Earth orbits the Sun, and as the moon orbits the Earth. Geophysical measurements are often recorded as time-series with GPS location. Signal processing involves the correction of time-series data for unwanted noise or errors introduced by the measurement platform, such as aircraft vibrations in gravity data. It also involves the reduction of sources of noise, such as diurnal corrections in magnetic data. In seismic data, electromagnetic data, and gravity data, processing continues after error corrections to include computational geophysics which result in
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#17327918778366240-461: The Earth's crust to the rebound due to the release of the pressure ), geological features such as mountains or ocean trenches , tectonic plate dynamics, and natural disasters can further distort the planet's shape. Evidence from seismology , heat flow at the surface, and mineral physics is combined with the Earth's mass and moment of inertia to infer models of the Earth's interior – its composition, density, temperature, pressure. For example,
6360-483: The Earth's magnetic field and earthquakes – have been investigated since the ancient era . The magnetic compass existed in China back as far as the fourth century BC. It was used as much for feng shui as for navigation on land. It was not until good steel needles could be forged that compasses were used for navigation at sea; before that, they could not retain their magnetism long enough to be useful. The first mention of
6480-454: The Earth's mean specific gravity ( 5.515 ) is far higher than the typical specific gravity of rocks at the surface ( 2.7–3.3 ), implying that the deeper material is denser. This is also implied by its low moment of inertia ( 0.33 M R , compared to 0.4 M R for a sphere of constant density). However, some of the density increase is compression under the enormous pressures inside the Earth. The effect of pressure can be calculated using
6600-520: The Earth's moon from others, while in poetry "Luna" has been used to denote personification of the Moon. Cynthia / ˈ s ɪ n θ i ə / is another poetic name, though rare, for the Moon personified as a goddess, while Selene / s ə ˈ l iː n iː / (literally 'Moon') is the Greek goddess of the Moon. The English adjective pertaining to the Moon is lunar , derived from the Latin word for
6720-421: The Earth's permanent magnetic field. The distribution of telluric current density can be used to detect variations in electrical resistivity of underground structures. Geophysicists can also provide the electric current themselves (see induced polarization and electrical resistivity tomography ). Electromagnetic waves occur in the ionosphere and magnetosphere as well as in Earth's outer core . Dawn chorus
6840-429: The Earth, due to gravitational anomalies from impact basins. Its shape is more elongated than current tidal forces can account for. This 'fossil bulge' indicates that the Moon solidified when it orbited at half its current distance to the Earth, and that it is now too cold for its shape to restore hydrostatic equilibrium at its current orbital distance. The Moon is by size and mass the fifth largest natural satellite of
6960-469: The Earth-Moon system might be explained by the post-impact mixing of the vaporized material that formed the two, although this is debated. The impact would have released enough energy to liquefy both the ejecta and the Earth's crust, forming a magma ocean. The liquefied ejecta could have then re-accreted into the Earth–Moon system. The newly formed Moon would have had its own magma ocean ; its depth
7080-530: The Earth. The newly formed Moon settled into a much closer Earth orbit than it has today. Each body therefore appeared much larger in the sky of the other, eclipses were more frequent, and tidal effects were stronger. Due to tidal acceleration , the Moon's orbit around Earth has become significantly larger, with a longer period. Following formation, the Moon has cooled and most of its atmosphere has been stripped. The lunar surface has since been shaped by large impact events and many small ones, forming
7200-504: The Moon approximately 10 minutes, taking 5 minutes to rise, and 5 minutes to fall. On average, 120 kilograms of dust are present above the Moon, rising up to 100 kilometers above the surface. Dust counts made by LADEE 's Lunar Dust EXperiment (LDEX) found particle counts peaked during the Geminid , Quadrantid , Northern Taurid , and Omicron Centaurid meteor showers , when the Earth, and Moon pass through comet debris. The lunar dust cloud
7320-458: The Moon derived from the impactor, rather than the proto-Earth. However, models from 2007 and later suggest a larger fraction of the Moon derived from the proto-Earth. Other bodies of the inner Solar System such as Mars and Vesta have, according to meteorites from them, very different oxygen and tungsten isotopic compositions compared to Earth. However, Earth and the Moon have nearly identical isotopic compositions. The isotopic equalization of
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#17327918778367440-495: The Moon for longer than just one lunar orbit. The topography of the Moon has been measured with laser altimetry and stereo image analysis . Its most extensive topographic feature is the giant far-side South Pole–Aitken basin , some 2,240 km (1,390 mi) in diameter, the largest crater on the Moon and the second-largest confirmed impact crater in the Solar System . At 13 km (8.1 mi) deep, its floor
7560-466: The Moon formed around 50 million years after the origin of the Solar System . Historically, several formation mechanisms have been proposed, but none satisfactorily explains the features of the Earth–Moon system. A fission of the Moon from Earth's crust through centrifugal force would require too great an initial rotation rate of Earth. Gravitational capture of a pre-formed Moon depends on an unfeasibly extended atmosphere of Earth to dissipate
7680-455: The Moon is a crescent\decrescent, [REDACTED] \ [REDACTED] , for example in M ☾ 'lunar mass' (also M L ). The lunar geological periods are named after their characteristic features, from most impact craters outside the dark mare , to the mare and later craters, and finally the young, still bright and therefore readily visible craters with ray systems like Copernicus or Tycho . Isotope dating of lunar samples suggests
7800-508: The Moon's solar illumination varies much less with season than on Earth and it allows for the existence of some peaks of eternal light at the Moon's north pole , at the rim of the crater Peary . The surface is exposed to drastic temperature differences ranging from 120 °C to −171 °C depending on the solar irradiance . Because of the lack of atmosphere, temperatures of different areas vary particularly upon whether they are in sunlight or shadow, making topographical details play
7920-403: The Moon, lūna . Selenian / s ə l iː n i ə n / is an adjective used to describe the Moon as a world, rather than as a celestial object, but its use is rare. It is derived from σελήνη selēnē , the Greek word for the Moon, and its cognate selenic was originally a rare synonym but now nearly always refers to the chemical element selenium . The element name selenium and
8040-494: The Solar System relative to their primary planets. The Moon's diameter is about 3,500 km, more than a quarter of Earth's, with the face of the Moon comparable to the width of either Mainland Australia , Europe or the Contiguous United States (which excludes Alaska , etc.). The whole surface area of the Moon is about 38 million square kilometers, comparable to North and South America combined,
8160-467: The Solar System, categorizable as one of its planetary-mass moons , making it a satellite planet under the geophysical definitions of the term . It is smaller than Mercury and considerably larger than the largest dwarf planet of the Solar System, Pluto . While the minor-planet moon Charon of the Pluto-Charon system is larger relative to Pluto, the Moon is the largest natural satellite of
8280-426: The Sun completely during a total solar eclipse . From Earth about 59% of the lunar surface is visible over time due to cyclical shifts in perspective ( libration ), making parts of the far side of the Moon visible. The Moon has been an important source of inspiration and knowledge for humans, having been crucial to cosmography , mythology, religion , art, time keeping , natural science , and spaceflight . In 1959,
8400-624: The Van Allen radiation belts. Geophysical measurements are generally at a particular time and place. Accurate measurements of position, along with earth deformation and gravity, are the province of geodesy . While geodesy and geophysics are separate fields, the two are so closely connected that many scientific organizations such as the American Geophysical Union , the Canadian Geophysical Union and
8520-436: The aim of investigating different energy, mineral and water resources. This is done through the uses of various remote sensing platforms such as; satellites , aircraft , boats , drones , borehole sensing equipment and seismic receivers . These equipment are often used in conjunction with different geophysical methods such as magnetic , gravimetry , electromagnetic , radiometric , barometry methods in order to gather
8640-475: The application of satellite altimetry technology to the mapping of the marine gravitational field in the early 1990s, the application of modelling methods to 3D seismic survey planning, the development of High-Density 3D (HD3D) technology for seismic exploration, the introduction of Multi-Azimuth and Wide-Azimuth 3D technology into the Asia-Pacific region, the introduction of Dual-Sensor Streamer technology to
8760-425: The calculation of the measurement derivative such as the first-vertical derivative. Many geophysics companies have designed in-house geophysics programs that pre-date ArcGIS and GeoSoft in order to meet the visualization requirements of a geophysical dataset. Exploration geophysics is a branch of applied geophysics that involves the development and utilization of different seismic or electromagnetic methods which
8880-484: The changes in acceleration experienced by spacecraft as they orbit has allowed fine details of the gravity fields of the planets to be mapped. For example, in the 1970s, the gravity field disturbances above lunar maria were measured through lunar orbiters , which led to the discovery of concentrations of mass, mascons , beneath the Imbrium , Serenitatis , Crisium , Nectaris and Humorum basins. Since geophysics
9000-413: The combined American landmass having an area (excluding all islands) of 37.7 million square kilometers. The Moon's mass is 1/81 of Earth's, being the second densest among the planetary moons, and having the second highest surface gravity , after Io , at 0.1654 g and an escape velocity of 2.38 km/s ( 8 600 km/h; 5 300 mph) . The Moon is a differentiated body that
9120-461: The concentration and distribution of radioisotopes near the Earth's surface, which is useful for mapping lithology and alteration. Fluid motions occur in the magnetosphere, atmosphere , ocean, mantle and core. Even the mantle, though it has an enormous viscosity , flows like a fluid over long time intervals. This flow is reflected in phenomena such as isostasy , post-glacial rebound and mantle plumes . The mantle flow drives plate tectonics and
9240-433: The crust and mantle. The absence of such neutral species (atoms or molecules) as oxygen , nitrogen , carbon , hydrogen and magnesium , which are present in the regolith , is not understood. Water vapor has been detected by Chandrayaan-1 and found to vary with latitude, with a maximum at ~60–70 degrees; it is possibly generated from the sublimation of water ice in the regolith. These gases either return into
9360-579: The data. The remote sensing platforms used in exploration geophysics are not perfect and need adjustments done on them in order to accurately account for the effects that the platform itself may have on the collected data. For example, when gathering aeromagnetic data (aircraft gathered magnetic data) using a conventional fixed-wing aircraft- the platform has to be adjusted to account for the electromagnetic currents that it may generate as it passes through Earth's magnetic field . There are also corrections related to changes in measured potential field intensity as
9480-480: The debris from a giant impact between Earth and a hypothesized Mars-sized body called Theia . The lunar surface is covered in lunar dust and marked by mountains , impact craters , their ejecta , ray-like streaks , rilles and, mostly on the near side of the Moon, by dark maria ("seas"), which are plains of cooled lava . These maria were formed when molten lava flowed into ancient impact basins. The Moon is, except when passing through Earth's shadow during
9600-399: The deduction that compasses point north due to the Earth itself being a giant magnet. In 1687 Isaac Newton published his work titled Principia which was pivotal in the development of modern scientific fields such as astronomy and physics . In it, Newton both laid the foundations for classical mechanics and gravitation , as well as explained different geophysical phenomena such as
9720-447: The dense mare basaltic lava flows that fill those basins. The anomalies greatly influence the orbit of spacecraft about the Moon. There are some puzzles: lava flows by themselves cannot explain all of the gravitational signature, and some mascons exist that are not linked to mare volcanism. The Moon has an external magnetic field of less than 0.2 nanoteslas , or less than one hundred thousandth that of Earth . The Moon does not have
9840-514: The depressions associated with impact basins , though the Moon's largest expanse of basalt flooding, Oceanus Procellarum , does not correspond to an obvious impact basin. Different episodes of lava flows in maria can often be recognized by variations in surface albedo and distinct flow margins. As the maria formed, cooling and contraction of the basaltic lava created wrinkle ridges in some areas. These low, sinuous ridges can extend for hundreds of kilometers and often outline buried structures within
9960-554: The distance between the two satellites using GPS and a microwave ranging system. Gravity variations detected by GRACE include those caused by changes in ocean currents; runoff and ground water depletion; melting ice sheets and glaciers. Satellites in space have made it possible to collect data from not only the visible light region, but in other areas of the electromagnetic spectrum . The planets can be characterized by their force fields: gravity and their magnetic fields , which are studied through geophysics and space physics. Measuring
10080-542: The dynamics of tectonic plates . The geopotential surface called the geoid is one definition of the shape of the Earth. The geoid would be the global mean sea level if the oceans were in equilibrium and could be extended through the continents (such as with very narrow canals). The Earth is cooling, and the resulting heat flow generates the Earth's magnetic field through the geodynamo and plate tectonics through mantle convection . The main sources of heat are: primordial heat due to Earth's cooling and radioactivity in
10200-478: The earth is not entirely spherical but instead generally exhibits an ellipsoid shape- which is a result of the centrifugal forces the planet generates due to its constant motion. These forces cause the planets diameter to bulge towards the Equator and results in the ellipsoid shape . Earth's shape is constantly changing, and different factors including glacial isostatic rebound (large ice sheets melting causing
10320-561: The earth up to several kilometers deep and are used to increase our understanding of the geology as well as to explore for oil and gas. Changes in the travel direction, called refraction , can be used to infer the deep structure of the Earth . Earthquakes pose a risk to humans . Understanding their mechanisms, which depend on the type of earthquake (e.g., intraplate or deep focus ), can lead to better estimates of earthquake risk and improvements in earthquake engineering . Although we mainly notice electricity during thunderstorms , there
10440-468: The energy of the passing Moon. A co-formation of Earth and the Moon together in the primordial accretion disk does not explain the depletion of metals in the Moon. None of these hypotheses can account for the high angular momentum of the Earth–Moon system. The prevailing theory is that the Earth–Moon system formed after a giant impact of a Mars -sized body (named Theia ) with the proto-Earth . The oblique impact blasted material into orbit about
10560-422: The expansion of plasma clouds. These clouds are generated during large impacts in an ambient magnetic field. This is supported by the location of the largest crustal magnetizations situated near the antipodes of the giant impact basins. The Moon has an atmosphere so tenuous as to be nearly vacuum , with a total mass of less than 10 tonnes (9.8 long tons; 11 short tons). The surface pressure of this small mass
10680-1182: The exposed ones. Conversely, mare lava has obscured many impact melt sheets and pools. Impact melts are formed when intense shock pressures from collisions vaporize and melt zones around the impact site. Where still exposed, impact melt can be distinguished from mare lava by its distribution, albedo, and texture. Sinuous rilles , found in and around maria, are likely extinct lava channels or collapsed lava tubes . They typically originate from volcanic vents , meandering and sometimes branching as they progress. The largest examples, such as Schroter's Valley and Rima Hadley , are significantly longer, wider, and deeper than terrestrial lava channels, sometimes featuring bends and sharp turns that again, are uncommon on Earth. Mare volcanism has altered impact craters in various ways, including filling them to varying degrees, and raising and fracturing their floors from uplift of mare material beneath their interiors. Examples of such craters include Taruntius and Gassendi . Some craters, such as Hyginus , are of wholly volcanic origin, forming as calderas or collapse pits . Such craters are relatively rare, and tend to be smaller (typically
10800-488: The fifth largest and most massive moon overall, and larger and more massive than all known dwarf planets . Its surface gravity is about one sixth of Earth's, about half of that of Mars , and the second highest among all Solar System moons, after Jupiter 's moon Io . The body of the Moon is differentiated and terrestrial , with no significant hydrosphere , atmosphere , or magnetic field . It formed 4.51 billion years ago, not long after Earth's formation , out of
10920-487: The final interpretation of the geophysical data into a geological interpretation of the geophysical measurements Geophysics emerged as a separate discipline only in the 19th century, from the intersection of physical geography , geology , astronomy , meteorology, and physics. The first known use of the word geophysics was in German ("Geophysik") by Julius Fröbel in 1834. However, many geophysical phenomena – such as
11040-510: The first human-made objects to leave Earth and reach another body arrived at the Moon, with the flyby of the Soviet Union 's Luna 1 and the intentional impact of Luna 2 . In 1966, the Moon became the first extraterrestrial body with a soft landing by Luna 9 and a orbital insertion by Luna 10 were achieved . On July 20, 1969, humans for the first time landed on the Moon and any extraterrestrial body, at Mare Tranquillitatis with
11160-427: The flood lavas that erupted onto the surface from partial melting in the mantle confirm the mafic mantle composition, which is more iron-rich than that of Earth. The crust is on average about 50 kilometres (31 mi) thick. The Moon is the second-densest satellite in the Solar System, after Io . However, the inner core of the Moon is small, with a radius of about 350 kilometres (220 mi) or less, around 20% of
11280-554: The flow in the Earth's core drives the geodynamo. Geophysical fluid dynamics is a primary tool in physical oceanography and meteorology . The rotation of the Earth has profound effects on the Earth's fluid dynamics, often due to the Coriolis effect . In the atmosphere, it gives rise to large-scale patterns like Rossby waves and determines the basic circulation patterns of storms. In the ocean, they drive large-scale circulation patterns as well as Kelvin waves and Ekman spirals at
11400-594: The geodynamo and plate tectonics. The main heat-producing isotopes are potassium-40 , uranium-238 , uranium-235, and thorium-232 . Radioactive elements are used for radiometric dating , the primary method for establishing an absolute time scale in geochronology . Unstable isotopes decay at predictable rates, and the decay rates of different isotopes cover several orders of magnitude, so radioactive decay can be used to accurately date both recent events and events in past geologic eras . Radiometric mapping using ground and airborne gamma spectrometry can be used to map
11520-409: The history of navigation. The first seismic instrument was built in 132 AD. Isaac Newton applied his theory of mechanics to the tides and the precession of the equinox ; and instruments were developed to measure the Earth's shape, density and gravity field, as well as the components of the water cycle. In the 20th century, geophysical methods were developed for remote exploration of the solid Earth and
11640-471: The lander Eagle of the United States ' Apollo 11 mission. Five more crews were sent between then and 1972, each with two men landing on the surface. The longest stay was 75 hours by the Apollo 17 crew. Since then, exploration of the Moon has continued robotically, and crewed missions are being planned to return beginning in the late 2020s. The usual English proper name for Earth's natural satellite
11760-436: The largest international professional society for the geophysical community. Geophysicist Geophysics ( / ˌ dʒ iː oʊ ˈ f ɪ z ɪ k s / ) is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists, who usually study geophysics, physics , or one of
11880-421: The magma ocean had crystallized, lower-density plagioclase minerals could form and float into a crust atop. The final liquids to crystallize would have been initially sandwiched between the crust and mantle, with a high abundance of incompatible and heat-producing elements. Consistent with this perspective, geochemical mapping made from orbit suggests a crust of mostly anorthosite . The Moon rock samples of
12000-521: The mantle could be responsible for prolonged activities on the far side in the Orientale basin. The lighter-colored regions of the Moon are called terrae , or more commonly highlands , because they are higher than most maria. They have been radiometrically dated to having formed 4.4 billion years ago, and may represent plagioclase cumulates of the lunar magma ocean. In contrast to Earth, no major lunar mountains are believed to have formed as
12120-406: The mare. Another result of maria formation is the creation of concentric depressions along the edges, known as arcuate rilles . These features occur as the mare basalts sink inward under their own weight, causing the edges to fracture and separate. In addition to the visible maria, the Moon has mare deposits covered by ejecta from impacts. Called cryptomares, these hidden mares are likely older than
12240-524: The near side of the Moon, and cover 31% of the surface of the near side compared with 2% of the far side. This is likely due to a concentration of heat-producing elements under the crust on the near side, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt. Most of the Moon's mare basalts erupted during the Imbrian period , 3.3–3.7 billion years ago, though some being as young as 1.2 billion years and as old as 4.2 billion years. In 2006,
12360-440: The near-side. Causes of the distribution of the lunar highlands on the far side are also not well understood. Topological measurements show the near side crust is thinner than the far side. One possible scenario then is that large impacts on the near side may have made it easier for lava to flow onto the surface. The Moon is a very slightly scalene ellipsoid due to tidal stretching, with its long axis displaced 30° from facing
12480-415: The ocean surface. In the Earth's core, the circulation of the molten iron is structured by Taylor columns . Waves and other phenomena in the magnetosphere can be modeled using magnetohydrodynamics . The physical properties of minerals must be understood to infer the composition of the Earth's interior from seismology , the geothermal gradient and other sources of information. Mineral physicists study
12600-427: The ocean, and geophysics played an essential role in the development of the theory of plate tectonics. Geophysics is applied to societal needs, such as mineral resources , mitigation of natural hazards and environmental protection . In exploration geophysics , geophysical survey data are used to analyze potential petroleum reservoirs and mineral deposits, locate groundwater, find archaeological relics, determine
12720-694: The oil and gas industry., the development and commercialization of the Multi-Level Source solution for 'broadband' seismic, the development of the Simultaneous Long Offset method for efficiently acquiring ultra-long offset marine seismic surveys, and the adaptation of Separated Wavefield Imaging to improve marine seismic survey efficiency. He has lectured extensively on the applications of 'broadband' seismic technologies, with particular emphasis upon ultra-low frequency benefits and challenges, providing professional courses on behalf of
12840-407: The planets upper crust. There is also some contributions from phase transitions . Heat is mostly carried to the surface by thermal convection , although there are two thermal boundary layers – the core–mantle boundary and the lithosphere – in which heat is transported by conduction . Some heat is carried up from the bottom of the mantle by mantle plumes . The heat flow at the Earth's surface
12960-400: The position in two coordinates and is more difficult to use than GPS. However, it is useful for measuring motions of the Earth such as nutation and Chandler wobble . Relative positions of two or more points can be determined using very-long-baseline interferometry . Gravity measurements became part of geodesy because they were needed to related measurements at the surface of the Earth to
13080-432: The possibility of a much warmer lunar mantle than previously believed, at least on the near side where the deep crust is substantially warmer because of the greater concentration of radioactive elements. Evidence has been found for 2–10 million years old basaltic volcanism within the crater Lowell, inside the Orientale basin. Some combination of an initially hotter mantle and local enrichment of heat-producing elements in
13200-587: The prefix seleno- (as in selenography , the study of the physical features of the Moon) come from this Greek word. Artemis , the Greek goddess of the wilderness and the hunt, came to also be identified as the goddess of the Moon ( Selene ) and was sometimes called Cynthia , after her birthplace on Mount Cynthus . Her Roman equivalent is Diana . The names Luna, Cynthia, and Selene are reflected in technical terms for lunar orbits such as apolune , pericynthion and selenocentric . The astronomical symbol for
13320-436: The radius of the Moon. Its composition is not well understood, but is probably metallic iron alloyed with a small amount of sulfur and nickel; analyzes of the Moon's time-variable rotation suggest that it is at least partly molten. The pressure at the lunar core is estimated to be 5 GPa (49,000 atm). On average the Moon's surface gravity is 1.62 m/s ( 0.1654 g ; 5.318 ft/s ), about half of
13440-605: The reference coordinate system. Gravity measurements on land can be made using gravimeters deployed either on the surface or in helicopter flyovers. Since the 1960s, the Earth's gravity field has been measured by analyzing the motion of satellites. Sea level can also be measured by satellites using radar altimetry , contributing to a more accurate geoid . In 2002, NASA launched the Gravity Recovery and Climate Experiment (GRACE), wherein two twin satellites map variations in Earth's gravity field by making measurements of
13560-471: The regolith because of the Moon's gravity or are lost to space, either through solar radiation pressure or, if they are ionized, by being swept away by the solar wind's magnetic field. Studies of Moon magma samples retrieved by the Apollo missions demonstrate that the Moon had once possessed a relatively thick atmosphere for a period of 70 million years between 3 and 4 billion years ago. This atmosphere, sourced from gases ejected from lunar volcanic eruptions,
13680-435: The seafloor. These stripes provide quantitative information on seafloor spreading , a part of plate tectonics. They are the basis of magnetostratigraphy , which correlates magnetic reversals with other stratigraphies to construct geologic time scales. In addition, the magnetization in rocks can be used to measure the motion of continents. Radioactive decay accounts for about 80% of the Earth's internal heat , powering
13800-404: The source. The locations of earthquakes provide information on plate tectonics and mantle convection. Recording of seismic waves from controlled sources provides information on the region that the waves travel through. If the density or composition of the rock changes, waves are reflected. Reflections recorded using Reflection Seismology can provide a wealth of information on the structure of
13920-460: The surface gravity of Mars and about a sixth of Earth's. The Moon's gravitational field is not uniform. The details of the gravitational field have been measured through tracking the Doppler shift of radio signals emitted by orbiting spacecraft. The main lunar gravity features are mascons , large positive gravitational anomalies associated with some of the giant impact basins, partly caused by
14040-424: The thickness of glaciers and soils, and assess sites for environmental remediation . Geophysics is a highly interdisciplinary subject, and geophysicists contribute to every area of the Earth sciences , while some geophysicists conduct research in the planetary sciences . To provide a more clear idea on what constitutes geophysics, this section describes phenomena that are studied in physics and how they relate to
14160-446: The winter solstice in the north polar crater Hermite . This is the coldest temperature in the Solar System ever measured by a spacecraft, colder even than the surface of Pluto . Blanketed on top of the Moon's crust is a highly comminuted (broken into ever smaller particles) and impact gardened mostly gray surface layer called regolith , formed by impact processes. The finer regolith, the lunar soil of silicon dioxide glass, has
14280-424: Was initially in hydrostatic equilibrium but has since departed from this condition. It has a geochemically distinct crust , mantle , and core . The Moon has a solid iron-rich inner core with a radius possibly as small as 240 kilometres (150 mi) and a fluid outer core primarily made of liquid iron with a radius of roughly 300 kilometres (190 mi). Around the core is a partially molten boundary layer with
14400-401: Was twice the thickness of that of present-day Mars . The ancient lunar atmosphere was eventually stripped away by solar winds and dissipated into space. A permanent Moon dust cloud exists around the Moon, generated by small particles from comets. Estimates are 5 tons of comet particles strike the Moon's surface every 24 hours, resulting in the ejection of dust particles. The dust stays above
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