|
|
Craters-Mona_Lisa_Crater-PCF-LXTT-00.jpgMagellan Probe: radio image of Mona Lisa Crater110 visiteL'età media della superficie di Venere è di circa 500 milioni di anni ed una delle domande più interessanti attiene la causa dell'attuale aspetto della superficie del Pianeta (una "lastra di lava").
Forse una serie ravvicinata di eventi cataclismici occorsi, appunto, circa 500 milioni di anni fa i quali hanno causato l'esplosione simultanea di migliaia di vulcani (con conseguenze catastrofiche evidenti) oppure l'effetto di lenti, ma costanti e lunghissimi, processi di accumulo e deposito di materiali eiettati dagli innumerevoli vulcani che tutt'ora costellano - ed illuminano - la superficie del Pianeta?
|
|
Craters-Mona_Lisa_Crater-PCF-LXTT-01.jpgMona Lisa Crater (Natural Colors; credits: Lunar Explorer Italia)56 visitenessun commentoMareKromium
|
|
Craters-Somerville_Crater-PIA00100.jpgMagellan Probe: radio image of fractured Somerville Crater70 visiteCaption NASA originale:"This Magellan radar image is of a 'half crater' located in the rift between Rhea and Theia Montes in Beta Regio on Venus. The unnamed crater is 37 Km in diameter and is located at 29,9° North latitude and 282,9° East longitude. It has been cut by many fractures or faults since it was formed by the impact of a large asteroid. The eastern half of the crater was destroyed during the formation of a fault valley that is up to 20 Km wide and apparently quite deep. A north-south profile through the very center of this crater is visible as a result of the down dropping and removal of the eastern half of the crater".
|
|
Craters-Stephania_Crater-PIA00475.jpgStephania Crater (possible Natural Colors; credits: Dr Paolo C. Fienga - Lunexit Team)54 visiteCrater Stephania is located at 51,3° Norh Latitude and 333,3° East Longitude in Northern Sedna Planitia.
With a diameter of about 11 Km (6,8 miles), Stephania is one of the smaller Craters on Venus.
Because many small meteoroids disintegrate during their passage through the dense Venusian atmosphere, there is an absence of craters smaller than 3 Km (approx. 1,9 miles) in diameter, and even craters smaller than 25 Km (15,5 miles) are relatively scarce.
The apron of ejected material suggests that the impacting body made contact with the Surface from an oblique angle. Upon closer observation it is possible to delineate secondary craters, impact scars from blocks ejected from the primary crater.
A feature associated with this and many other Venusian Craters is a radar-dark halo.
Since dark radar return signifies a smooth surface, it has been hypothesized that an intense shock wave removed or pulverized previously rough surface material or that a blanket of fine material was deposited during or after the impact.MareKromium
|
|
Craters-Unnamed_Complex_Crater-PIA00462-PCF-LXTT-IPF.jpgUnnamed Complex Crater (Possible Absolute Natural Colors; credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/Italian Planetary Foundation)81 visiteThe NASA - Magellan Spacecraft imaged this multiple-Floored, highly Irregular Impact Crater at Latitude 16,4° North and Longitude 352,1° East, during its 481st and 482nd orbits around the Planet Venus (on Earth, it was September, 27, 1990). This Impact Crater, about 9,2 Km (such as approx. 5,7 miles) in maximum diameter, was formed on what appears to be a slightly fractured, radar-dark (---> smooth) Venusian Plain. The abundant, low viscosity Flows associated with this Impact Event have, however, filled local Fault-controlled Troughs (---> Graben). These shallow Grabens are well portrayed on this Magellan image but they would have been unrecognizable if they had not (coincidentally) been infillled by the radar-bright Crater Flows.
This fortuitous enhancement by the Crater Flows - of Fault Structures - that were below the resolution capacity of the Magellan Synthetic Aperture Radar provided the Magellan Science Team with valuable Geologic information. For instance, the Flow Deposits from this Impact Crater are now thought to consist - primarily - of "Shock Melted Rock" (---> such as a remarkable quantity of almost liquid rocky material that got pushed away and outwards by the powerful shock-wave/s that followed the original Impact Event/s) and Fragmented Debris resulting from the nearly simultaneous impacts of 2 (two) projectile fragments into the hot (---> approx. 426° Celsius - or about 800 degrees Farheneit) Surface Rocks of Venus. On the other hand, the presence of various Floors in this highly Irregular Impact Crater is interpreted to be the result of Crushing, Fragmentation, and eventual Aerodynamic Dispersion of a single entry projectile (---> meteor) during its passage through the dense Venusian Atmosphere.
This frame (which is an Original NASA - Magellan Spacecraft Radio-Image published on the NASA - Planetary Photojournal with the n. PIA 00462), since it is just a Radio-Image of the Venusian Surface and NOT a real view of it, has been colorized, according to an educated guess carried out by Dr Paolo C. Fienga (LXTT-IPF), in what they could reasonably be its possible Absolute Natural Colors (such as the colors that a human eye would perceive if someone were onboard the NASA - Magellan Spacecraft and, once the thick layer of Venusian Clouds and Fogs is completely overcome, looked down, towards the Surface of Venus itself), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.MareKromium
|
|
Craters-Unnamed_Crater-PIA00468.jpgUnnamed (and heavily degraded) Crater (possible Natural Colors; credits: Dr Paolo C. Fienga - Lunexit Team)54 visiteDuring orbits 423 through 424 on 22 September 1990, Magellan imaged this Impact Crater that is located at Latitude 10,7° North and Longitude 340,7° East.
This Crater is shown as a representative of Venusian Craters that are of the proper diameter (about 15 Km) to be 'transitional' in their morphology between 'complex' and irregular'.
Complex Craters account for about 96% of all craters on Venus with diameters larger than about 15 Km; they are thought to have been formed by the impact of a large, more or less intact, mass of asteroidal material that has not been excessively effected during its passage through the dense Venusian Atmosphere.
Complex Craters are characterized by circular Rims, terraced Inner Wall Slopes, well developed Ejecta Deposits, and flat Floors with a Central Peak or Peak Ring.
Irregular Craters make up about 60% of the Craters with diameters less than about 15 Km. Irregular Craters are thought to form as the result of the impact of asteroidal projectiles that have been aerodynamically crushed and fragmented during their passage through the Atmosphere.
Irregular craters are characterized by irregular and/or discontinuous Rims and hummocky or multiple Floors.
The 'Transitional' Crater shown here has a somewhat circular Rim like larger Complex Craters, but has the hummocky Floor and asymmetric Ejecta characteristic of smaller Irregular Craters. MareKromium
|
|
Craters-Unnamed_Craters-Lakshmi_Region-PIA00477.jpgPossible Remnants of a Meteoroid in Lakshmi Region (possible Natural Colors; credits: Dr Paolo C. Fienga - Lunexit Team)54 visiteThis full resolution mosaiced image covers an area of approx. 100 by 120 Km (such as about 62 by 74 miles) and is located in the Lakshmi Region of Venus, at 47° North Latitude and 334° East Longitude.
Due to the dense Venusian Atmosphere, Primary Impact Craters of less than a 3 Km (a little less than 2 miles) diameter are nonexistent.
The dark circular region and associated central bright feature in this image are thought to be the remnants of a Meteoroid smaller than the size necessary to create an Impact Crater, and entering the Atmosphere at low velocity (approx. 350 meters/second.)
The central bright feature appears to be a cluster of small secondary impacts, ejecta and debris from the original meteor that broke up in the Atmosphere.
Even though most of the meteorite did not hit the Surface, the Atmospheric Shock wave could be great enough to modify the surrounding region. One explanation for this radar dark circular formation, called "Dark Margins", could be that the shock wave was energetic enough to pulverize the Surface (smooth surfaces generally appear radar dark).
Another explanation is that the Surface could be blanketed by a fine material that was formed by the original meteor's breakup through the Atmosphere.
More than half of the Impact Craters on Venus have associated Dark Margins, and most of these are prominently located left of center of the rater. This is another effect which could be caused by the extremely dense Atmosphere of Venus. MareKromium
|
|
Craters-Unnamed_Craters_in_Lavinia_Planitia-PIA00103.jpg3D view of impact craters in Lavinia Planitia (simulated colors)85 visiteCaption NASA originale:"Three impact craters are displayed in this 3D perspective view of the surface of Venus. The center of the image is located at approx. 27° South latitude, 339° East longitude in the NWestern portion of Lavinia Planitia. The viewpoint is located SW of Howe Crater, which appears centered in the lower portion of the image. Howe is a crater with a diameter of 37,3 Km. Danilova, a crater with a diameter of 47,6 Km, appears above and to the left of Howe in the image. Aglaonice, a crater with a diameter of 62,7 Km, is shown to the right of Danilova.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".
|
|
Craters-Wanda_Crater-PIA00250.jpgMagellan Probe: radio image of "Wanda" Impact Crater in Akna Montes92 visiteCaption NASA originale:"This Magellan full-resolution image show the northern part of the Akna Montes. The Akna range is a North-South trending ridge belt that forms the western border of the elevated smooth plateau of Lakshmi Planum. 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 LR) with a diameter of 22 Km 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".
|
|
Hestia_Rupes-PIA00469.jpgComplex Network of Narrow Fractures near Hestia Rupes Region (possible Natural Colors; credits: Dr Paolo C. Fienga - Lunexit Team)54 visiteThis is a Magellan radar image covering an about 105- Km (approx. 63-mile) by 45-Km (approx. 27-mile) Region near Hestia Rupes on the North-Western corner of Aphrodite Terra.
The complex network of narrow (such as <1 Km) Fractures in the center of the image extends for approx. 50 Km (about 31 miles). This network exhibits tributary-like branches similar to those observed in river systems on Earth. However, the angular intersections of the tributaries suggest tectonic control.
These features appear to be due to drainage of lava along preexisting fractures and subsequent collapse of the Surface. The underlying tectonic fabric can be observed in the North-East trending Ridges which predate the Plains.MareKromium
|
|
Lakhshmi_Planum-PIA00249.jpgMagellan Probe: radio image of Lakhsmi Planum and Danu Montes75 visiteCaption NASA originale:"Southwest Lakshmi Planum is bounded on the south by the Danu Montes. Lakshmi Planum is an elevated plateau that is bounded on all sides by mountain chains. Here, the Danu mountains have an angular fractured appearance. Chasms slice diagonally across the mountains in the lower left (southwest) corner of the image. Because of the steep slopes and the local relief of the mountains of several kilometers, these fault-bounded troughs appear to zig-zag through the mountains when, in fact, they are probably straight if viewed from above. The radar view provides a perspective that would place the viewer's eye to the right, 27° above the horizon. Thus, slopes facing to the right can be seen completely, though dark, and slopes facing away to the left appear shortened, often seen only as thin bright lines. In the center of the image is a low volcanic dome 20 Km in diameter. This type of volcanic feature frequently occurs on the low plains. This dome on the edge of Lakshmi is deformed and faulted where it has been affected by the forces that created the Danu mountains".
|
|
Lakshmi_Planum-PIA00249.jpgDanu Montes and Lakshmi Planum (possible Natural Colors; credits: Dr Paolo C. Fienga - Lunexit Team)54 visiteSouthwest Lakshmi Planum is bounded on the South by the Danu Montes.
Lakshmi Planum is an elevated plateau plain that is bounded on all sides by mountain chains. Here, the Danu Mountains have an angular fractured appearance. Chasms slice diagonally across the mountains in the lower left (South-West) corner of the image. Because of the steep slopes and the local relief of the mountains of several kilometers (2-3 miles, these fault-bounded troughs appear to zig-zag through the mountains when, in fact, they are probably straight if viewed from above.
The radar view provides a perspective that would place the viewer's eye to the right, 27° above the Horizon. Thus, slopes facing to the right can be seen completely, though dark, and slopes facing away to the left appear shortened, often seen only as thin bright lines. In the center of the image is a low volcanic dome (approx. 20 Km - about 12 miles - in diameter).
This type of volcanic feature frequently occurs on the low plains. This dome on the edge of Lakshmi is deformed and faulted where it has been affected by the forces that created the Danu mountains.
The image is approx. 75 Km (about 46 miles) on a side. The center is at 60° North Latitude and 324,5° East Longitude.MareKromium
|
|
| 126 immagini su 11 pagina(e) |
 |
3 | |
|
|
|
|
|
|
|
