"Magellan radar image [is] of Addams crater, Venus. The radar bright outflow associated with the 90 km crater stretches over 600 km to the east. (North is up.) The crater is located at 56.1S,98.9E in the Aino Planitia region."
Astrogeology[edit | edit source]
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."
Volcanoes[edit | edit source]
"A portion of the eastern edge of Alpha Regio is displayed in this three-dimensional perspective view [on the right] of the surface of Venus. The viewpoint is located at approximately 30 degrees south latitude, 11.8 degrees east longitude at an elevation of 2.4 kilometers (3.8 miles). The view is to the northeast at the center of an area containing seven circular dome-like hills. The average diameter of the hills is 25 kilometers (15 miles) with maximum heights of 750 meters (2,475 feet). Three of the hills are visible in the center of the image. Fractures on the surrounding plains are both older and younger than the domes. The hills may be the result of viscous or thick eruptions of lava coming from a vent on the relatively level ground, allowing the lava to flow in an even lateral pattern. The concentric and radial fracture patterns on their surfaces suggests that a chilled outer layer formed, then further intrusion in the interior stretched the surface. An alternative interpretation is that domes are the result of shallow intrusions of molten lava, causing the surface to rise. If they are intrusive, then magma withdrawal near the end of the eruptions produced the fractures. The bright margins possibly indicate the presence of rock debris or talus at the slopes of the domes. Resolution of the Magellan data is about 120 meters (400 feet). Magellan's synthetic aperture radar is combined with radar altimetry to develop a three-dimensional map of the surface. A perspective view is then generated from the map. Simulated color and a process called radar-clinometry are used to enhance small-scale structures. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. The image was produced by the JPL Multimission Image Processing Laboratory."
In the second image on the right is "a 225 meter per pixel Magellan radar image mosaic of Venus, centered at 47 degrees south latitude, 25 degrees east longitude in the Lada region. The scene is approximately 550 kilometers (341 miles) east-west by 630 kilometers (391 miles) north-south. The mosaic shows a system of east-trending radar-bright and dark lava flows encountering and breaching a north-trending ridge belt (left of center). Upon breaching the ridge belt, the lavas pool in a vast, radar-bright deposit (covering approximately 100,000 square kilometers [right side of image]). The source caldera for the lava flows, named Ammavaru, lies approximately 300 kilometers (186 miles) west of the scene."
The third image down on the right is Magellan radar image of a lava channel on Venus. This unusually long channel ranges from Fortuna Tessera in the north down to the eastern Sedna Planitia in the south. The channel is about 2 km wide and shows branches and islands along its length. The framelet shown here is about 50 km wide, and north is up.
On the right, fourth image down, "Magellan's radar system detected few impact craters in the process of being resurfaced by volcanism. Alcott is the largest of these craters in transition, with a diameter of 63 km (39 mi). The trough-like depression (lower left) is a rille through which lava once flowed. A remnant of rough radial ejecta is preserved outside the crater's southeast rim. The presence of partially lava-flooded craters such as this is important to our understanding of the rate of resurfacing on Venus by volcanism."
Structural geology[edit | edit source]
"Arachnoids are large structures of unknown origin that have been found only on the surface of Venus. Arachnoids get their name from their resemblance to spider-webs. They appear as concentric ovals surrounded by a complex network of fractures, and can span 200 kilometers. Radar echoes from the Magellan spacecraft that orbited Venus from 1990 to 1994 built up this image. Over 30 arachnoids have been identified on Venus, so far. The Arachnoid might be a strange relative to the volcano, but possibly different arachnoids are formed by different processes."
The second image down on the right shows the northern part of the Akna Montes (mountains) of Venus and an apparent impact crater.
"The Akna range is a north-south trending ridge belt that forms the western border of the elevated smooth plateau of Lakshmi Planum (plains). The Lakshmi plateau plains are formed by extensive volcanic eruptions and are bounded by mountain chains on all sides. The plains appear to be deformed near the mountains. This suggests that some of the mountain building activity occurred after the plains formed. An impact crater (Official International Astronomical Union name 'Wanda,' mapped first by the Soviet Venera 15/16 mission in 1984 at low resolution) with a diameter of 22 kilometers (14 miles) was formed by the impact of an asteroid in the Akna mountains. The crater has a rugged central peak and a smooth radar-dark floor, probably volcanic material. The crater does not appear to be much deformed by later crustal movement that uplifted the mountains and crumpled the plains. Material from the adjacent mountain ridge to the west, however, appears to have collapsed into the crater. Small pits seen to the north of the crater may be volcanic collapse pits a few kilometers across (1-2 miles). The ridge of the Akna mountains immediately to the west of the crater is 8 kilometers wide (5 miles). The area imaged is approximately 200 kilometers long and 125 kilometers wide (130 by 80 miles). This area is centered at 71.5 degrees north latitude, 324 degrees east longitude. The resolution of the Magellan radar system is 120 meters (400 feet). At this latitude the radar views the surface from an angle of 23 degrees off vertical, creating a perspective as though a viewer were looking at the scene from the right (east) at an angle of 23 degrees above the surface."
Bright, lineated terrain of Alpha Regio is a series of troughs, ridges, and faults running in every direction in the third image down on the right.
"The lengths of these features range from 10 km (6.3 mi) to 60 km (37 mi). The elevation of Alpha Regio varies over a range of 4 km (2.5 mi). Low-lying areas appear dark in the radar images and may be filled with lava. Volcanoes appear as bright spots on the smooth plains. Notice the large volcano in the upper right. At the center of this 35 km (22 mi) volcano is a caldera; its western edge appears to be either a debris flow or a lava flow. The black square represents missing data."
Seven circular domes are imaged in the fourth down on the right.
"They average 25 km (15 mi) in diameter with maximum heights of 750 m (2475 ft). Some scientists believe they are the result of eruptions of thick lava that flowed from a vent on level ground, resulting in an even lateral pattern of lava. The concentric and radial fracture pattern on the surface of the domes suggests that lava welled up inside the domes, causing the surface to stretch."
This region in the fifth image down on the right is one of the most rugged on Venus. The terrain is made up of tessera, which are interlacing ridges and valleys.
Hypotheses[edit | edit source]
- Venus has been added between the Earth and the Sun in recorded history.
- The atmosphere of Venus is that of a volcanic planet.
- Magnetic field reversals of the Sun occur with the sunspot cycle which may have its origins in enhanced electron currents from Jupiter and Venus when perihelion is coincident.
- Venus is often confused with Aphrodite (the Moon).
- Venus has "a core of metallized silicates".
- Venus has "an iron core".
- "A chondritic composition of the whole planet" with hypothesis 1.
- "a chondritic mantle" composition with hypothesis 2.
- "a uniform distribution of radioactivity" is a stage of the thermal history of Venus.
- "radioactive elements from the upper 1 000 km were gradually carried out into the crust." is a stage of the thermal history of Venus.
- "This transport [of radioactive elements begins] at the start of the melting of the mantle".
- "The mantle of Venus, as that of the Earth [is] a mixture of different minerals and [melts] in some interval of temperatures [...] of the order of 200°."
- "In the core the melting [occurs] at constant temperature for each given depth."
- "The core [has] a metallic conductivity independent of the temperature."
"Preliminary estimates by Safronov (1965, 1969) of the initial temperature of the Earth were used to choose initial temperatures of Venus and Mercury."
The "molecular conductivity of amorphous matter does not decrease with temperature (as it does in crystalline bodies)."
The "molecular conductivity ceases to depend on temperature with the onset of melting."
For hypothesis 1, the "core of metallized silicates is liquid at the present moment."
For hypothesis 2, "the core is liquid with temperature 12 400 °K."
See also[edit | edit source]
References[edit | edit source]
- DR Watts (26 March 2003). Addams Crater, Venus and outflow. Greenbelt, Maryland USA: NASA Goddard Space Flight Center. http://nssdc.gsfc.nasa.gov/imgcat/html/object_page/mgn_c260s093_202.html. Retrieved 2015-02-04.
- Sue Lavoie (8 February 1996). PIA00233: Venus - 3D Perspective View of Eistla Regio. Pasadena, California USA: NASA/JPL. http://photojournal.jpl.nasa.gov/catalog/PIA00233. Retrieved 2015-02-03.
- Dan Crichton (10 May 2005). Impact Craters. Pasadena, California USA: NASA/JPL. http://pds.jpl.nasa.gov/planets/captions/venus/dsnall.htm. Retrieved 2015-02-03.
- Eric De Jong; Jeff Hall; Myche McAuley; Randy Kirk (13 March 1996). PIA00246: Venus - 3D Perspective View of Eastern Edge of Alpha Regio. Pasadena, California USA: NASA/JPL. http://photojournal.jpl.nasa.gov/catalog/PIA00246. Retrieved 2015-02-03.
- Sue Lavoie (14 November 1996). PIA00486: Venus - System of Lava Flows and Ridge Belt. Pasadena, California USA: NASA/JPL. http://photojournal.jpl.nasa.gov/catalog/PIA00486. Retrieved 2015-02-04.
- Dan Crichton; Betty Sword; Colleen Schroeder (10 May 2005). Craters in Transition. Pasadena, California USA: NASA/JPL. http://pds.jpl.nasa.gov/planets/captions/venus/alcott.htm. Retrieved 2015-02-04.
- Robert Nemiroff; Jerry Bonnell (20 January 1998). Arachnoids on Venus. Washington, DC USA: NASA. http://apod.nasa.gov/apod/ap980120.html. Retrieved 2015-02-03.
- Sue Lavoie (14 March 1996). PIA00250: Venus - Wanda Crater in Akna Montes. Pasadena, California USA: NASA/JPL. http://photojournal.jpl.nasa.gov/catalog/PIA00250. Retrieved 2015-02-04.
- Dan Crichton; Betty Sword; Colleen Schroeder (10 May 2010). Ridges and Troughs. Pasadena, California USA: NASA/JPL. http://pds.jpl.nasa.gov/planets/captions/venus/alpha.htm. Retrieved 2015-02-04.
- Dan Crichton; Betty Sword; Colleen Schroeder (10 May 2005). Domical Hills. Pasadena, California USA: NASA/JPL. http://pds.jpl.nasa.gov/planets/captions/venus/pancakes.htm. Retrieved 2015-02-04.
- S. V. Majeva (1969). "The Thermal History of the Terrestrial Planets". Astrophysical Letters 4: 11-6. http://adsabs.harvard.edu/full/1969ApL.....4...11M. Retrieved 2015-10-15.
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