Draft:Original research/Astrogeology

The image shows a portion of the San Andreas Fault in California USA on Earth. Credit: Robert E. Wallace, USGS.

Astrogeology is the study of naturally occurring astronomical rocky objects, their physical structure and substance, history and origin, and the processes that act on them, especially by examination of their rocks.

Foliation

The image shows finely layered slate perhaps with occasional dolomite layers exposed on a beach in Cornwall, UK. Credit: Si Griffiths.

The image shows folds in slate and quartzite of the Meguma Group near the Ovens, Nova Scotia, Canada. Credit: Michael C. Rygel.

Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression. Slate is frequently grey in color, especially when seen, en masse, covering roofs. However, slate occurs in a variety of colors even from a single locality; for example, slate from North Wales can be found in many shades of grey, from pale to dark, and may also be purple, green or cyan.

Theoretical astrogeology

This geologic province map depicts features approximately 150 km across and greater due to the fact that the resolution of the maps is consistent with the resolution of the seismic refraction data. Credit: USGS.

Here's a couple of theoretical definition:

Def. the intellectual and practical activity encompassing the systematic study through observation and experiment of naturally occurring astronomical rocky objects, their physical structure and substance, history and origin, and the processes that act on them, especially by examination of their rocks, is called astrogeology.

Def. the astronomy of observing on or in astronomical objects so as to geologically match up likely parallel evolution is called astrogeology.

Identifying the rocks, regoliths, and sediments on the solid surface of the Earth is often best accomplished from above the surface.

Beta particles

Main resources: Radiation astronomy/Beta particles, Beta particle astronomy, and Beta particles

Excessive "²⁶Mg [has] been reported in meteoritic carbonaceous chondrites [...] which demonstrate an excess of ²⁶Mg of up to 40% combined with essentially solar concentrations of ²⁴Mg and ²⁵Mg. Many of the data are well correlated with the ²⁷Al content of the samples, and this is interpreted as evidence that the excess ²⁶Mg has arisen from the in situ decay (via positron emission and electron capture) of the ground state of ²⁶Al in these minerals."

Ultraviolets

Main resources: Radiation astronomy/Ultraviolets, Ultraviolet astronomy, and Ultraviolets

This is a black-and-white image of 2 Pallas taken with the Hubble Telescope in 2007 with UV filter. Credit: Hubble Space Telescope/STScI.{{free media}}

"Spectrally blue (B-type) asteroids are rare, with the second discovered asteroid, Pallas, being the largest and most famous example."

"[T]he negative optical spectral slope of some B-type asteroids is due to the presence of a broad absorption band centered near 1.0 μm. The 1 μm band can be matched in position and shape using magnetite (Fe₃O₄), which is an important indicator of past aqueous alteration in the parent body. ... Observations of B-type asteroid (335) Roberta in the 3 μm region reveal an absorption feature centered at 2.9 μm, which is consistent with the absorption due to phyllosilicates (another hydration product) observed in CI chondrites. ... at least some B-type asteroids are likely to have incorporated significant amounts of water ice and to have experienced intensive aqueous alteration."

Visuals

Main resources: Radiation astronomy/Visuals, Visual astronomy, and Visuals

This is a landscape painting. Credit: Martin Johnson Heade.

Def. a "portion of land or territory which the eye can comprehend in a single view, including all the objects it contains" is called a landscape.

Def. each continuous surface of a landscape that is observable in its entirety and has consistence of form or regular change of form is called a landform.

Def. "[t]he study of landforms, their classification, origin, development, and history" is called geomorphology.

Mercury

Main pages: Wanderers/Mercury and Draft:Mercury

The crater in the lower right-hand corner of this image has a patch of very dark material located near its centre. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

This image shows a double-ring impact basin, with another large impact crater on its south-south-western side. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

The so-called 'Weird terrain' on Mercury, at the antipodal point of the en:Caloris Basin. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

Discovery Rupes is an escarpment on Mercury. Credit: NASA/JPL/Northwestern University.

Representation is of the thrust fault at Discovery Rupes. Credit: NASA.

"The crater in the lower right-hand corner of this image [on the right] has a patch of very dark material located near its center. The region of this image has been seen only with the Sun high overhead in the sky. Such lighting conditions are good for recognizing color differences of rocks but not well suited for ascertaining the topography of surface features from shadows. The shape of the surface in this area is difficult to resolve given the lighting angle, but the dark patch is not in shadow. Dark surfaces have also been seen on other regions of Mercury, including this dark halo imaged during the second Mercury flyby (PIA11357) and near such named craters as Nawahi, Atget, and Basho seen during MESSENGER's first Mercury encounter. The example here is particularly striking, however, and from this NAC image the material may appear even darker than in other example areas. The dark color is likely due to rocks that have a different mineralogical composition from that of the surrounding surface. Understanding why these patches of dark rocks are found on Mercury's surface is a question of interest to the MESSENGER Science Team. The right edge of the image here aligns with this previously released NAC image (see PIA11763), where other dark surface material, as well as patches of light-colored rocks, can be seen."

The second lower image on the right from the top shows "a double-ring impact basin, with another large impact crater on its south-south-western side. Double-ring basins are formed naturally when a large meteoroid strikes the surface of a rocky planet. Smaller, more recent impacts also formed comparatively fresh craters across the entire surface visible in this image. The floor within the inner or peak ring appears to be smoother than the floor between the peak ring and the outer rim, possibly the result of lava flows that partially flooded the basin some time after impact."

The lowest image from the top on the right is a closeup of the weird terrain of Mercury.

"Weird terrain best describes this hilly, lineated region of Mercury. Scientists note that this area is at the antipodal point to the large Caloris basin. The shock wave produced by the Caloris impact may have been reflected and focused to the antipodal point, thus jumbling the crust and breaking it into a series of complex blocks. The area covered is about 800 km (497 mi) on a side."

"One of the most prominent lobate scarps (Discovery Scarp) [on the left], photographed by Mariner 10 during it's first encounter with Mercury, is located at the center of this image (extending from the top to near bottom). This scarp is about 350 kilometers long and transects two craters 35 and 55 kilometers in diameter. The maximum height of the scarp south of the 55-kilometer crater is about 3 kilometers. Notice the shallow older crater (near the center of the image) perched on the crest of the scarp."

"The Mariner 10 mission [...] explored Venus in February 1974 on the way to three encounters with Mercury-in March and September 1974 and in March 1975."

Venus

Main resource: Wanderers/Venus

The planet Venus is shown here rotating in a clockwise motion. Credit: Ironchew and NASA.

A portion of western Eistla Regio is displayed in this three-dimensional perspective view of the surface of Venus. Credit: NASA/JPL.

Magellan radar image is of the "crater farm". Credit: Magellan Team, JPL, NASA.

The rotating globe on the right is the radar surface of Venus using the radar scanner of the Magellan probe.

On the second lower right is an image of a "portion of western Eistla Regio is displayed in this three-dimensional perspective view of the surface of Venus. The viewpoint is located 1,310 kilometers (812 miles) southwest of Gula Mons at an elevation of 0.78 kilometer (0.48 mile). The view is to the northeast with Gula Mons appearing on the horizon. Gula Mons, a 3 kilometer (1.86 mile) high volcano, is located at approximately 22 degrees north latitude, 359 degrees east longitude. The impact crater Cunitz, named for the astronomer and mathematician Maria Cunitz, is visible in the center of the image. The crater is 48.5 kilometers (30 miles) in diameter and is 215 kilometers (133 miles) from the viewer's position. Magellan synthetic aperture radar data is combined with radar altimetry to develop a three-dimensional map of the surface. Rays cast in a computer intersect the surface to create a three-dimensional perspective view. Simulated color and a digital elevation map developed by the U.S. Geological Survey, are used to enhance small-scale structure. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. The image was produced at the JPL Multimission Image Processing Laboratory and is a single frame from a video released [on] March 5, 1991, [...]."

Third image down on the right is a Magellan radar image of the "crater farm", showing the craters (clockwise from top left) Danilova, Aglaonice, and Saskia centered at 27 S, 339 E. Aglaonice is 65 km in diameter.

"Three large impact craters with diameters ranging from 37 km (23 mi) to 65 km (40 mi) are visible in the fractured plains. Features typical of meteorite impact craters are also visible. Rough radar-bright ejecta surrounds the perimeter of the craters; terraced inner walls and large central peaks can be seen. Crater floors appear dark because they are smooth and have been flooded by lava. Domes of probable volcanic origin can be seen in the southeastern corner. The domes range in diameter from 1-12 km (0.6-7 mi); some have central pits typical of volcanic shields or cones."

Earth

Main resource: Keynote lectures/Earth

File:Ice cap.jpg

This is an aerial image of the ice cap on Ellesmere Island, Canada. Credit: National Snow and Ice Data Center.

This oblique astronaut photograph from the International Space Station (ISS) captures a white-to-grey volcanic ash and steam plume extending westwards from the Soufriere Hills volcano. Credit: NASA Expedition 21 crew.

This is an aerial view of the Barringer Meteor Crater about 69 km east of Flagstaff, Arizona. Credit:D. Roddy, U.S. Geological Survey.

The first image on the right is an aerial image of the ice cap on Ellesmere Island, Canada.

Oblique images such as the one on the second lower right are taken by astronauts looking out from the ISS at an angle, rather than looking straight downward toward the Earth (a perspective called a nadir view), as is common with most remotely sensed data from satellites. An oblique view gives the scene a more three-dimension quality, and provides a look at the vertical structure of the volcanic plume. While much of the island is covered in green vegetation, grey deposits that include pyroclastic flows and volcanic mud-flows (lahars) are visible extending from the volcano toward the coastline. When compared to its extent in earlier views, the volcanic debris has filled in more of the eastern coastline. Urban areas are visible in the northern and western portions of the island; they are recognizable by linear street patterns and the presence of bright building rooftops. The silver-grey appearance of the Caribbean Sea surface is due to sun-glint, which is the mirror-like reflection of sunlight off the water surface back towards the hand-held camera on-board the ISS. The sun-glint highlights surface wave patterns around the island.

The image on the left is an aerial view of the Barringer Meteor Crater. Fragments of an iron-nickel meteorite have been found in the crater confirming its origin as an impact crater.

Moon

Main pages: Wanderers/Moon and Draft:Moon

Planetary geologist and NASA astronaut Harrison "Jack" Schmitt collects lunar samples during the Apollo 17 mission. Credit: NASA.

In the image at right, planetary geologist and NASA astronaut Harrison "Jack" Schmitt collects lunar samples during the Apollo 17 mission.

Mars

Main resources: Wanderers/Mars and Keynote lectures/Mars

Close-up of gullies with multiple channels; patterned ground is also visible in this hirise image taken under the HiWish program, location is 41 S and 206 E. Credit: Jim Secosky modified NASA/JPL/University of Arizona image.

This image shows a cross-section of a portion of the north polar ice cap of Mars. Credit: NASA.

This image is a SHARAD subsurface radargram of Mars. Credit: NASA/JPL-Caltech/ASI/University of Rome/Washington Universtiy in St. Louis.

This mosaic of images shows a boulder-sized rock called "Strathdon," which is made up of many complex layers. Credit: NASA/JPL-Caltech/MSSS.{{free media}}

This mosaic of images shows layers of ancient sediment on a boulder-sized rock called "Strathdon," as seen by the Mars Hand Lens Imager (MAHLI) camera on the end of the robotic arm on NASA's Curiosity rover. Credit: NASA/JPL-Caltech/MSSS.{{free media}}

Image on the top right is a close-up of gullies with multiple channels on Mars.

The image at right "shows a cross-section of a portion of the north polar ice cap of Mars, derived from data acquired by the Mars Reconnaissance Orbiter's Shallow Radar (SHARAD), one of six instruments on the spacecraft. The data depict the region's internal ice structure, with annotations describing different layers. The ice depicted in this graphic is approximately 2 kilometers (1.2 miles) thick and 250 kilometers (155 miles) across. White lines show reflection of the radar signal back to the spacecraft. Each line represents a place where a layer sits on top of another. Scientists study how thick the pancake-like layers are, where they bulge and how they tilt up or down to understand what the surface of the ice sheet was like in the past as each new layer was deposited."

At lower right is a "radargram from the Shallow Subsurface Radar instrument (SHARAD)".

The "Shallow Subsurface Radar instrument (SHARAD) on NASA's Mars Reconnaissance Orbiter [radargram] is shown in the upper-right panel and reveals detailed structure in the polar layered deposits of the south pole of Mars."

"The sounding radar collected the data presented here during orbit 1334 of the mission, on Nov. 8, 2006."

"The horizontal scale in the radargram is distance along the ground track. It can be referenced to the ground track map shown in the lower right. The radar traversed from about 75 to 85 degrees south latitude, or about 590 kilometers (370 miles). The ground track map shows elevation measured by the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor orbiter. Green indicates low elevation; reddish-white indicates higher elevation. The traverse proceeds up onto a plateau formed by the layers."

"The vertical scale on the radargram is time delay of the radar signals reflected back to Mars Reconnaissance Orbiter from the surface and subsurface. For reference, using an assumed velocity of the radar waves in the subsurface, time is converted to depth below the surface at one place: about 1,500 meters (5,000 feet) to one of the deeper subsurface reflectors. The color scale varies from black for weak reflections to white for strong reflections."

"The middle panel shows mapping of the major subsurface reflectors, some of which can be traced for a distance of 100 kilometers (60 miles) or more. The layers are not all horizontal and the reflectors are not always parallel to one another. Some of this is due to variations in surface elevation, which produce differing velocity path lengths for different reflector depths. However, some of this behavior is due to spatial variations in the deposition and removal of material in the layered deposits, a result of the recent climate history of Mars."

"The Shallow Subsurface Radar was provided by the Italian Space Agency (ASI). Its operations are led by the University of Rome and its data are analyzed by a joint U.S.-Italian science team."

The fourth image down on the right is a "mosaic of images shows a boulder-sized rock called "Strathdon," which is made up of many complex layers. NASA's Curiosity Mars rover took these images using its Mast Camera, or Mastcam, on July 9, 2019, the 2,461st Martian sol, or day, of the mission."

"The color in the image has been adjusted to approximate white balancing to resemble how the rocks and sand would appear under daytime lighting conditions on Earth."

The fifth image down on the right is a "mosaic of images shows layers of ancient sediment on a boulder-sized rock called "Strathdon," as seen by the Mars Hand Lens Imager (MAHLI) camera on the end of the robotic arm on NASA's Curiosity rover. The images were taken on July 10, 2019, the 2,462nd Martian day, or sol, of the mission."

"The images were acquired from about 4 inches (10 centimeters) away and processed to adjust brightness and remove blemishes."

Callisto

Main page: Draft:Callisto

Two landslides 3–3.5 km long are visible on the right sides of the floors of the two large craters on the right. Credit: .

Views of eroding (top) and mostly eroded (bottom) ice knobs (~100 m high), possibly formed from the ejecta of an ancient impact. Credit: NASA/JPL/Arizona State University, Academic Research Lab.

The Galileo images also revealed small, dark, smooth areas with overall coverage less than 10,000 km², which appear to embay [To embay means to shut in, or shelter, as in a bay.] the surrounding terrain. They are possible cryovolcanic deposits. Both the light and the various smooth plains are somewhat younger and less cratered than the background cratered plains.

Small patches of pure water ice with an albedo as high as 80% are found on the surface of Callisto, surrounded by much darker material. High-resolution Galileo images showed the bright patches to be predominately located on elevated surface features: crater rims, scarps, ridges and knobs. They are likely to be thin water frost deposits. Dark material usually lies in the lowlands surrounding and mantling bright features and appears to be smooth. It often forms patches up to 5 km across within the crater floors and in the intercrater depressions.

On a sub-kilometer scale the surface of Callisto is more degraded than the surfaces of other icy Galilean moons. Typically there is a deficit of small impact craters with diameters less than 1 km as compared with, for instance, the dark plains on Ganymede. Instead of small craters, the almost ubiquitous surface features are small knobs and pits. The knobs are thought to represent remnants of crater rims degraded by an as-yet uncertain process.

The most likely candidate process is the slow sublimation of ice, which is enabled by a temperature of up to 165 K, reached at a subsolar point. Such sublimation of water or other volatiles from the dirty ice that is the bedrock causes its decomposition. The non-ice remnants form debris avalanches descending from the slopes of the crater walls. Such avalanches are often observed near and inside impact craters and termed "debris aprons". Sometimes crater walls are cut by sinuous valley-like incisions called "gullies", which resemble certain Martian surface features. In the ice sublimation hypothesis, the low-lying dark material is interpreted as a blanket of primarily non-ice debris, which originated from the degraded rims of craters and has covered a predominantly icy bedrock.

"Recent Galileo images [top left] of the surface of Jupiter's moon Callisto have revealed large landslide deposits within two large impact craters seen in the right side of this image. The two landslides are about 3 to 3.5 kilometers (1.8 to 2.1 miles) in length. They occurred when material from the crater wall failed under the influence of gravity, perhaps aided by seismic disturbances from nearby impacts. These deposits are interesting because they traveled several kilometers from the crater wall in the absence of an atmosphere or other fluids which might have lubricated the flow. This could indicate that the surface material on Callisto is very fine-grained, and perhaps is being "fluffed" by electrostatic forces which allowed the landslide debris to flow extended distances in the absence of an atmosphere."

"This image was acquired on September 16th, 1997 by the Solid State Imaging (CCD) system on NASA's Galileo spacecraft, during the spacecraft's tenth orbit around Jupiter. North is to the top of the image, with the sun illuminating the scene from the right. The center of this image is located near 25.3 degrees north latitude, 141.3 degrees west longitude. The image, which is 55 kilometers (33 miles) by 44 kilometers (26 miles) across, was acquired at a resolution of 100 meters per picture element."

Views of eroding (top) and mostly eroded (bottom) ice knobs (~100 m high), possibly formed from the ejecta of an ancient impact are shown in the second images at left.

"The highest-resolution views ever obtained of any of Jupiter's moons, taken by NASA's Galileo spacecraft in May 2001, reveal numerous bright, sharp knobs covering a portion of Jupiter's moon Callisto."

"The knobby terrain seen throughout the top inset is unlike any seen before on Jupiter's moons. The spires are very icy but also contain some darker dust. As the ice erodes, the dark material apparently slides down and collects in low-lying areas. Over time, as the surface continues to erode, the icy knobs will likely disappear, producing a scene similar to the bottom inset. The number of impact craters in the bottom image indicates that erosion has essentially ceased in the dark plains shown in that image, allowing impact craters to persist and accumulate."

"The knobs are about 80 to 100 meters (260 to 330 feet) tall, and they may consist of material thrown outward from a major impact billions of years ago. The areas captured in the images lie south of Callisto's large Asgard impact basin."

"The smallest features discernable in the images are about 3 meters (10 feet) across."

Europa

Main pages: Rocks/Ice sheets/Europa and Draft:Europa

Approximate natural color (left) and enhanced color (right) is shown in these Galileo views of the leading hemisphere. Credit: NASA / JPL / University of Arizona.

Reddish spots and shallow pits pepper the enigmatic ridged surface of Europa in this view combining information from images taken by NASA's Galileo spacecraft during two different orbits around Jupiter. Credit: NASA/JPL/University of Arizona/University of Colorado.

Mosaic of Galileo images shows features indicative of internal geologic activity: lineae, lenticulae (domes, pits) and Conamara Chaos. Credit: NASA / JPL / Arizona State University.

Approximately natural color image of Europa by the Galileo spacecraft, shows lineae. Credit: NASA/JPL.

Craggy, 250 m high peaks and smooth plates are jumbled together in a close-up of Conamara Chaos. Credit: NASA/JPL.

This view of Jupiter's icy moon Europa shows a region shaped like a mitten. Credit: NASA/JPL/University of Arizona.

The darker regions are areas where Europa's primarily water ice surface has a higher mineral content. This surface is striated by cracks and streaks, while cratering is relatively infrequent. Other features present on Europa are circular and elliptical lenticulae (Latin for "freckles", reddish spots in the first image at left). Many are domes, some are pits and some are smooth, dark spots. Others have a jumbled or rough texture. The dome tops look like pieces of the older plains around them, suggesting that the domes formed when the plains were pushed up from below. The prominent markings crisscrossing the moon seem to be mainly albedo features, which emphasize low topography.

"Reddish spots and shallow pits pepper the enigmatic ridged surface of Europa in this view combining information from images taken by NASA's Galileo spacecraft during two different orbits around Jupiter."

"The spots and pits visible in this region of Europa's northern hemisphere are each about 10 kilometers (6 miles) across. The dark spots are called "lenticulae," the Latin term for freckles. Their similar sizes and spacing suggest that Europa's icy shell may be churning away like a lava lamp, with warmer ice moving upward from the bottom of the ice shell while colder ice near the surface sinks downward. Other evidence has shown that Europa likely has a deep melted ocean under its icy shell. Ruddy ice erupting onto the surface to form the lenticulae may hold clues to the composition of the ocean and to whether it could support life."

"The image combines higher-resolution information obtained when Galileo flew near Europa on May 31, 1998, during the spacecraft's 15th orbit of Jupiter, with lower-resolution color information obtained on June 28, 1996, during Galileo's first orbit."

Europa's most striking surface features are a series of dark streaks crisscrossing the entire globe, called lineae (lines). Close examination shows that the edges of Europa's crust on either side of the cracks have moved relative to each other. The larger bands are more than 20 km (12 mi) across, often with dark, diffuse outer edges, regular striations, and a central band of lighter material.

The third image at the right is a "view of the Conamara Chaos region on Jupiter's moon Europa taken by NASA's Galileo spacecraft shows an area where the icy surface has been broken into many separate plates that have moved laterally and rotated. These plates are surrounded by a topographically lower matrix. This matrix material may have been emplaced as water, slush, or warm flowing ice, which rose up from below the surface. One of the plates is seen as a flat, lineated area in the upper portion of the image. Below this plate, a tall twin-peaked mountain of ice rises from the matrix to a height of more than 250 meters (800 feet). The matrix in this area appears to consist of a jumble of many different sized chunks of ice. Though the matrix may have consisted of a loose jumble of ice blocks while it was forming, the large fracture running vertically along the left side of the image shows that the matrix later became a hardened crust, and is frozen today. The Brooklyn Bridge in New York City would be just large enough to span this fracture."

"North is to the top right of the picture, and the sun illuminates the surface from the east. This image, centered at approximately 8 degrees north latitude and 274 degrees west longitude, covers an area approximately 4 kilometers by 7 kilometers (2.5 miles by 4 miles). The resolution is 9 meters (30 feet) per picture element. This image was taken on December 16, 1997 at a range of 900 kilometers (540 miles) by Galileo's solid state imaging system."

"This view [third down on the left] of Jupiter's icy moon Europa shows a region shaped like a mitten that has a texture similar to the matrix of chaotic terrain, which is seen in medium and high resolution images of numerous locations across Europa's surface. Development of such terrain may be one of the major processes for resurfacing the moon. North is to the top and the sun illuminates the surface from the left. The material in the "catcher's mitt" has the appearance of frozen slush and seems to bulge upward from the adjacent surface, which has been bent downward and cracked, especially along the southwest (lower left) margins. Scientists on the Galileo imaging team are exploring various hypotheses for the formation of such terrain including solid-state convection (vertical movement between areas which differ in density due to heating), upwelling of viscous icy "lava," or liquid water melting through from a subsurface ocean."

"The image, centered at 20 degrees north latitude, 80 degrees west longitude covers an area approximately 175 by 180 kilometers (108 by 112 miles). The resolution is 235 meters per picture element. The images were taken on 31 May, 1998 Universal Time at a range of 23 thousand kilometers (14 thousand miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft."

Ganymede

Main resources: Rocks/Ice sheets/Ganymede, Ganymede ice sheets, and Ganymede

File:Ganpia02582.jpg

NASA's Galileo spacecraft took this image of dark terrain in Nicholson Regio, near the border with Harpagia Sulcus on Jupiter's moon Ganymede. Credit: NASA/JPL/Brown University.

"NASA's Galileo spacecraft took this image of dark terrain within Nicholson Regio, near the border with Harpagia Sulcus on Jupiter's moon Ganymede. The ancient, heavily cratered dark terrain is faulted by a series of scarps."

"The faulted blocks form a series of "stair-steps" like a tilted stack of books. On Earth, similar types of features form when tectonic faulting breaks the crust and the intervening blocks are pulled apart and rotate. This image supports the notion that the boundary between bright and dark terrain is created by that type of extensional faulting."

"North is to the right of the picture and the Sun illuminates the surface from the west (top). The image is centered at -14 degrees latitude and 320 degrees longitude, and covers an area approximately 16 by 15 kilometers (10 by 9 miles). The resolution is 20 meters (66 feet) per picture element. The image was taken on May 20, 2000, at a range of 2,090 kilometers (1,299 miles)."

Ariel

Main resources: Ariel and Rocks/Rocky objects/Ariel

The complex terrain of Ariel is viewed in this image, the best Voyager 2 color picture of the Uranian moon. Credit: NASA/JPL.

"The complex terrain of Ariel is viewed in [the image at right], the best Voyager 2 color picture of the Uranian moon. The individual photos used to construct this composite were taken Jan. 24, 1986, from a distance of 170,000 kilometers (105,000 miles. Voyager captured this view of Ariel's southern hemisphere through the green, blue and violet filters of the narrow-angle camera; the resolution is about 3 km (2 mi). Most of the visible surface consists of relatively intensely cratered terrain transected by fault scarps and fault-bounded valleys (graben). Some of the largest valleys, which can be seen near the terminator (at right), are partly filled with younger deposits that are less heavily cratered. Bright spots near the limb and toward the left are chiefly the rims of small craters. Most of the brightly rimmed craters are too small to be resolved here, although one about 30 km (20 mi) in diameter can be easily distinguished near the center. These bright-rim craters, though the youngest features on Ariel, probably have formed over a long span of geological time. Although Ariel has a diameter of only about 1,200 km (750 mi), it has clearly experienced a great deal of geological activity in the past."

Comets

Main resource: Radiation astronomy/Comets

File:Rosetta OSIRIS NAC comet 67P 20140803 2 625.jpg

This image shows Comet 67P/Churyumov-Gerasimenko. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/ UPM/DASP/IDA.

File:Rosetta OSIRIS NAC comet 67P 20140803 1 625.jpg

This image shows Comet 67P/Churyumov-Gerasimenko rotated around a vertical axis from the right. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/ UPM/DASP/IDA.

This is an image of the nucleus of Comet 67P/Churyumov-Gerasimenko by Rosetta. Credit: ESA Rosetta Mission.{{free media}}

Single frame Rosetta spacecrast NAVCAM image of Comet 67P/C-G was taken on 6 March from a distance of 82.9 km to the comet. Credit: ESA/Rosetta/NAVCAM.{{free media}}

Images taken by the Rosetta navigation camera (NAVCAM) on 19 September 2014 at 28.6 km (17.8 mi) from the centre of comet 67P/Churyumov–Gerasimenko. Credit: ESA/Rosetta/NAVCAM.{{free media}}

Four-image montage comprises images taken by Rosetta's navigation camera from a distance of 9.8 km from the centre of comet 67P/C-G – about 7.8 km from the surface. Credit: ESA/Rosetta/NAVCAM.{{free media}}

Image is taken by Rosetta's navigation camera from a distance of 9.8 km from the centre of comet 67P/C-G Credit: ESA/Rosetta/NAVCAM.{{free media}}

The image at the right is an optical astronomy image of the comet 67P/Churyumov-Gerasimenko. Rosetta's OSIRIS narrow-angle camera made the image on 3 August 2014 from a distance of 285 km. The image resolution is 5.3 metres/pixel.

The left image is rotated 90° from the right. The location of the right image is the front view of the left side just out of view in the left image. The object rotates by the right hand rule from the left image to the right.

Note that due to the evaporation of volatiles, the surface of the rocky object appears pitted or cratered.

"The short period comets have orbital periods <20 years and low inclination. Their orbits are controlled by Jupiter and thus they are also called Jupiter Family comets. [...]  Because the orbit crosses that of Jupiter, the comet will have gravitational interactions with this massive planet.  The objects orbit will gradually change from these interactions and eventually the object will either be thrown out of the Solar System or collide with a planet or the Sun."

Perihleion distance in AU = 1.243, eccentricity = 0.641, inclination = 7.0, and orbital period in years = 2.745.

Geochronology

File:Murchison meteorite grain.png

The grains in a scanning electron micrograph are of a dated presolar silicon carbide grain from the Murchison meteorite curated at the Field Museum in Chicago. Credit: Janaína N. Ávila.{{fairuse}}

"Stardust from half the lifetime of the universe ago fell to Earth in a meterorite 50 years ago, and is believed to be the oldest solid material ever found."

"Such 'presolar grains' are tiny and rare, only found in about 5% of meteorites that have fallen to Earth."

"These are the oldest solid materials ever found, and they tell us about how stars formed in our galaxy."

The "Field Museum has the largest portion of the Murchison meteorite, a treasure trove of presolar grains that fell in Victoria, Australia, in 1969. Presolar grains for this study were isolated from the Murchison meteorite about 30 years ago at the University of Chicago."

"By measuring how many of the new cosmic-ray produced elements are present in a pre-solar grain, scientists can tell how long it was exposed to cosmic rays, telling them how old it is. [...] Based on how many cosmic rays they had soaked up, most of the grains had to be 4.6 to 4.9 billion years old, and some grains were older than 5.5 billion years."

"Our hypothesis is that the majority of those grains, which are 4.6 to 4.9 billion years old, formed in an episode of enhanced star formation. There was a time before the start of the Solar System when more stars formed than normal."

Sedimentology

Main resource: Sediments/Sedimentology

This middle Triassic marginal marine sequence in southwestern Utah consists of siltstones and sandstones. Credit: Wilson44691.

Sedimentology encompasses the study of modern sediments such as sand, mud (silt), and clay, and the processes that result in their deposition.

Sedimentary rocks cover most of the Earth's surface, record much of the Earth's history, and harbor the fossil record. Sedimentology is closely linked to stratigraphy, the study of the physical and temporal relationships between rock layers or strata.

Structural geology

Main resource: Earth/Geology/Structures

The image shows rock strata in Cafayate, Argentina. Credit: travelwayoflife.

The image shows an anticline in the Barstow Formation (Miocene) at Calico Ghost Town near Barstow, California USA. Credit: Wilson44691.

The image at the right shows rock strata in Cafayate, Argentina, the subject of stratigraphy.

Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories.

Hypotheses

Main resource: Hypotheses

1. Geological forces found on Earth should be applicable to astronomical objects consisting of rocks.

See also

• Astrogeology (52 kB) (15 January 2020)
• Astrognosy (43 kB) (13 August 2019)
• Astrohistory (118 kB) (19 October 2019)
• Atmospheric sciences (39 kB) (15 December 2019)
• Callisto (45 kB) (7 December 2019)
• Ceres (31 kB) (6 December 2019)
• Charges (25 kB) (5 November 2019)
• Chemicals (189 kB) (4 October 2019)
• Classical mechanics (11 kB) (23 July 2019)
• Comets (36 kB) (6 December 2019)
• Conditions (8 kB) (23 October 2019)
• Craters by radiation (111 kB) (1 February 2019)
• Dione (17 kB) (26 October 2019)
• Distances (12 kB) (6 October 2019)
• Earth (124 kB) (23 July 2019)
• Electrospheres (14 kB) (3 November 2019)
• Enceladus (39 kB) (4 October 2019)
• Gases (23 kB) (27 October 2019)
• Geochemistry (26 kB) (10 August 2019)
• Geochronology (124 kB) (13 August 2019)
• Geographic coordinates (37 kB) (18 November 2019)
• Geology (95 kB) (4 March 2019‎)
• Geomorphology (71 kB) (13 August 2019)
• Geophysics (80 kB) (12 August 2019)
• Geoseismology (36 kB) (7 December 2019)
• Hydromorphology (56 kB) (10 July 2019)
• Interplanetary medium (105 kB) (1 April 2019‎)
• Interstellar medium (97 kB) (20 June 2019)
• Io (36 kB) (7 December 2019)
• Jupiter (108 kB) (16 August 2019)
• Liquids (37 kB) (12 August 2019)
• Mars (102 kB) (25 July 2019‎)
• Measurements (3 kB) (12 December 2019)
• Mercury (73 kB) (25 July 2019)
• Minerals (107 kB) (18 October 2019‎)
• Mining geology (24 kB) (16 August 2019)
• Moon (105 kB) (24 October 2019)
• Natural electric field of the Earth (27 kB) (10 December 2019)
• Oceanography (25 kB) (8 August 2019)
• Paleontology (115 kB) (4 October 2019)
• Petrophysics (40 kB) (7 November 2019)
• Planets (132 kB) (24 October 2019‎)
• Planets by radiation astronomy (110 kB) (26 July 2019‎)
• Plasmas (13 kB) (15 December 2019)
• Pluto (18 kB) (1 January 2020)
• Radiation (154 kB) (12 December 2019)
• Radiation astronomy (175 kB) (8 December 2019)
• Radiation physics (39 kB) (27 October 2019)
• Regions (20 kB) (13 December 2019)
• Rocks (65 kB) (26 January 2019‎)
• Saturn (153 kB) (14 September 2019)
• Sedimentary rocks (48 kB) (31 August 2019)
• Sediments (57 kB) (19 September 2019)
• Solar systems (95 kB) (31 December 2019)
• Solids (13 kB) (19 September 2019)
• Spaceflights (23 kB) (11 December 2019)
• Structural geology (60 kB) (9 September 2019)
• Titan (48 kB) (25 October 2019)
• Uranus (72 kB) (24 January 2019‎)
• Venus (87 kB) (25 October 2019)
• Vesta (35 kB) (6 December 2019)
• Volcanoes (100 kB) (8 December 2019)
• Wanderers (62 kB) (19 October 2019)

Further reading

• Autumn Burdick (December 16, 2000). PIA02582: Stair-step Scarps in Dark Terrain on Ganymede. Pasadena, California USA: NASA/JPL. http://photojournal.jpl.nasa.gov/catalog/PIA02582. Retrieved 2014-06-12. 

External links

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