Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!elroy.jpl.nasa.gov!jato!mars.jpl.nasa.gov!baalke From: baalke@mars.jpl.nasa.gov (Ron Baalke) Newsgroups: comp.graphics Subject: Magellan Images Keywords: Magellan Message-ID: <1991Mar25.012512.23477@jato.jpl.nasa.gov> Date: 25 Mar 91 01:25:12 GMT Sender: news@jato.jpl.nasa.gov Reply-To: baalke@mars.jpl.nasa.gov (Ron Baalke) Organization: Jet Propulsion Laboratory, Pasadena, CA. Lines: 190 Nntp-Posting-Host: mars.jpl.nasa.gov =================== MAGELLAN IMAGES March 24, 1991 =================== I've placed five more Magellan images in VICAR format and 18 in GIF format at the Ames SPACE archives, bringing the Magellan total to 19 VICAR images and 46 GIF images. All of the images are obtainable via anonymous ftp from ames.arc.nasa.gov (128.102.18.3), and are in the pub/SPACE/VICAR and pub/SPACE/GIF directories, respectively. All of the Magellan images I've uploaded to Ames are public release images from the Magellan project, and are in the public domain and can be freely distributed. The five new VICAR files and their sizes are: alpha.img 1,049,600 bytes lavin.img 1,049,600 bytes ovdac.img 1,574,400 bytes ovdan.img 3,147,776 bytes tick.img 2,347,458 bytes All of the VICAR images have a corresponding caption files (with a .txt extension) which contains detailed descriptions of the image. Make sure you are in binary mode when transferring the image files, and in ASCII mode when transferring the text files. The new caption files are appended to the end of this message. The VICAR images can be viewed on an IBM PC computer with the IMDISP program stored in a zip file called imdisp56.zip, located in the pub/SPACE/SOFTWARE directory. I am one of the programmers for IMDISP, and would welcome any feedback on the program. The VICAR format is used by the Image Processing Lab (MIPL) at JPL. Most of the VICAR images are in 1024x1024 pixel resolution and are about 1MB in size. I've converted all of the Magellan VICAR images into GIF format in 640x480, 256 color resolution. The new GIF files are: alpha.gif ovdac.gif alpha1.gif ovdac1.gif alpha2.gif ovdac2.gif alpha3.gif ovdac3.gif lavina.gif ovdan.gif lavina1.gif ovdan1.gif lavina2.gif ovdan2.gif tick.gif ovdan3.gif tick1.gif tick2.gif ============================================================================ ALPHA.TXT Thirty-six orbits of full-resolution data from the northern edge of central Alpha Regio are shown in this image. The image width is about 600 kilometers (375 miles). The bright lineated terrain is a series of troughs, ridges, and faults that are oriented in many directions. The lengths of these features generally range from 10 kilometers (6.3 miles) to 50 kilometers (31.3 miles). The topographic elevation within Alpha Regio varies over a range of 4 kilometers (2.5 miles). Local topographic lows, whose outlines are generally controlled by structures within the central region, are relatively radar-dark and filled with volcanic lavas. Source vents for this volcanism appear as bright spots within the smooth plains units. A distinct example of late-stage deformation of Alpha is the narrow band of southwest-northeast trending faults that disrupt older terrain between -20 degrees and -22 degrees latitude. Another interesting feature is the 35 kilometers (21.9 miles) diameter volcanic edifice located at the upper right of the image. The center of the volcano is a local topographic low and its western edge appears to be breached. ============================================================================ LAVIN.TXT This Magellan image mosiac located in the Lavinia region shows the crater Carson, a 38 km (23 mile) diameter crater. The image is centered at about 24 degrees south latitude, 344 degrees longitude. Impact craters in the Magellan data are frequently surrounded by radar-dark halos. Several of these halos were noted to have a hyperbolic shape, extending hundreds of kilometers to the west of the craters. Five of these dark halos were also seen extending out from craters in Magellan emissivity data. Magellan emissivity data, derived from the altimeter data, provides information about the porosity (soil versus solid rock) and the composition of the surface. The darkness in the emissivity data indicates a very smooth surface, leading to the interpretation that these halos may be thick, smooth sediment deposits formed by the 'crushing' blow of the atmosphere associated with the incoming projectile that formed the impact crater. But why are only about 5% of the craters surrounded by these halos? On the surface of most planets, the population of impact craters can be used to obtain both relative and absolute surface ages. On Venus, as on Earth, there are relatively few craters, making relative age dating (comparing one region of the planet to another) statistically difficult. The number of craters on Venus indicates that the surface may be only about 400 million years old. The dark halos may indicate the very youngest craters on the planet- where the harsh conditions on Venus have not yet caused these dark halos to 'roughen up' and disappear. The halos could possibly be used as 'geologic clocks.' Volcanic flows or tectonic structures cutting one of these halos are interpreted to have occurred even more recently than the craters. This image shows such a situation, where flows associated with the crater cut across the halo, indicating a very young age. Scientists are continuing to identify these halos in the Magellan data, and use them to understand the geologic evolution of the surface. ============================================================================ OVDAC.TXT This Magellan image shows part the interior of Ovda Regio, one of the large highlands ringing the equator of Venus. Several tectonic events formed this complex block-fractured terrain. An underlying fabric of ridges and valleys strikes NE-SW. These ridges are spaced 10-20 kilometers (6-12 miles) apart and may have been caused by shortening of the crust at right angles to this trend. These structures are cut by throughgoing extension fractures trending NW-SE, suggesting a later episode of NE-SW extension. Lastly, the largest valleys, particularly the 20 kilometer (12 mile)-wide one extending across the image, were filled with dark material, probably lava. The complex internal fabric of Ovda Regio attests to a long history of tectonic deformation. This image, centered approximately at 1 S 81 E, measures 225 kilometers (140 miles) by 150 kilometers (90 miles) and was acquired by Magellan in November 1990. ============================================================================ OVDAN.TXT This Magellan image shows part of the northern boundary of Ovda Regio, one of the large highlands ringing the equator of Venus. The scene consists largely of low-relief, rounded linear ridges. These ridges, 8-15 kilometers (5-9 miles) in width and 30-60 kilometers (20-40 miles) long, lie mostly along a 100-200 kilometer (60-120 mile) wide slope where the elevation drops 3 kilometers (2 miles) from Ovda Regio to the surrounding plains. Some of the ridges have been cut at right angles by extension fractures. Dark material, either lava or windblown dirt, fills the region between the ridges. The curvilinear, banded nature of these ridges suggests that crustal shortening, roughly oriented north-south, is largely responsible for their formation. Such crustal shortening was unexpected by Magellan scientists, who believed that Ovda Regio, a likely site of hot upwelling from the interior of Venus, should be dominated by volcanism and crustal extension. This image, centered approximately at 1 N 81 E, measures 300 kilometers (190 miles) by 225 kilometers (140 miles) and was acquired by Magellan in November 1990. ============================================================================ TICK.TXT This Magellan image is located in the Eistla Region of Venus in the southern hemisphere and is centered at 5.5 degrees east longitude, 18 degrees south latitude. It is 122.8 kilometers (76.1 miles) across east-west and 107.5 kilometers (66.6 miles) across north-south. North is oriented towards the top of the image. Shown in the image is an unusual volcanic edifice unlike all others previously observed. It is approximately 65.6 kilometers (40.7 miles) across at the base and has a relatively flat, slightly concave summit 34.8 kilometers (21.6 miles) in diameter. The sides of the edifice are characterized by radiating ridges and valleys that impart a fluted appearance to the construct. To the west, the rim of the edifice appears to have been breached by dark lava flows that emanated from a shallow summit pit approximately 5.4 kilometers (3.3 miles) in diameter and traveled west along a channel approximately 5.4 kilometers (3.3 miles) wide and 26.8 kilometers (16.6 miles) long. A series of coalescing, collapsed pits 2-10 kilometers (1.2-6.2 miles) in diameter are located 10 kilometers (6.2 miles) west of the summit rim. The edifice and western pits are circumscribed by faint, concentric lineaments up to 70.3 kilometers (43.6 miles) in diameter. A series of north-northwest-trending graben are deflected eastwards around the edifice; the interplay of these graben and the fluted rim of the edifice produce a distinctive scalloped pattern in the image. Several north-northwest-trending lineaments cut directly across the summit region. This peculiar volcanic construct is located 25-30 kilometers (15.5-18.6 miles) north of Alpha Regio, a highly deformed region of tessera terrain. A collection of at least 6 similar volcanoes has been observed near Thetis Regio, a region of tessera within Aphrodite Terra. Thus, these unusual constructs tentatively appear to be spatially associated with regions of tessera. The implications of this spatial association on the unusual morphology of these constructs are being investigated. ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@mars.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | ___| | | | |__) |/ | | |___ M/S 301-355 | Change is constant. /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | |_____|/ |_|/ |_____|/ |