Newsgroups: comp.archives Path: utzoo!utgpu!news-server.csri.toronto.edu!ox.com!emv From: baalke@mars.jpl.nasa.gov (Ron Baalke) Subject: [graphics] Magellan Images Message-ID: <1991Mar1.111407.22872@ox.com> Followup-To: comp.graphics Keywords: Magellan, JPL Sender: emv@ox.com (Edward Vielmetti) Reply-To: baalke@mars.jpl.nasa.gov (Ron Baalke) Organization: Jet Propulsion Laboratory, Pasadena, CA. References: <1991Mar1.051848.24864@jato.jpl.nasa.gov> Date: Fri, 1 Mar 1991 11:14:07 GMT Approved: emv@ox.com (Edward Vielmetti) X-Original-Newsgroups: comp.graphics Archive-name: astro/magellan/magellan-images/1991-03-01 Archive-directory: ames.arc.nasa.gov:/pub/SPACE/VICAR/ [128.102.18.3] Original-posting-by: baalke@mars.jpl.nasa.gov (Ron Baalke) Original-subject: Magellan Images Reposted-by: emv@ox.com (Edward Vielmetti) =================== MAGELLAN IMAGES February 28, 1991 =================== I've placed two more Magellan images at the Ames SPACE archives, bringing the Magellan total to 12 images. They can be obtained via anonymous ftp from ames.arc.nasa.gov (128.102.18.3), and are in the ftp/pub/SPACE/VICAR directory. The two new files are called arach.img and lavinia.img. All of these images are in VICAR format, and each image has a corresponding caption in text files (with a .txt extension) which contain detailed descriptions of the image. The two new caption files are appended to the end of this message. Most of the VICAR images are 1MB in size. 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 ftp/pub/SPACE/IMDISP directory. I've converted all of the Magellan images into GIF format in 640x480 resolution, and they can be retrieved from the ftp/pub/SPACE/GIF directory. I've decided to do something a little different this time. In order to fit the entire image into a pixel space of 640x480, I've had to subsample the image by a factor of 2 (equivalent to zooming out twice), and this resulted in some of the details in the images being lost. So I've created additional GIF images which zoom in on the more interesting features of the images. From the arach.img and lavinia.img images, there are 6 GIF files. The files arach.gif and lavinia.gif show the entire image. I've created arach1.gif and arach2.gif, which were extracted out of the arach.gif image and show a subsection of arach.gif, but in greater detail. Similarly, lavinia1.gif and lavinia1.gif were created from lavinia.gif. ============================================================================ ARACH.TXT Arachnoids, one of the more remarkable features found on Venus, are seen on radar-dark plains in this Magellan image mosaic in the Fortuna region. The image is centered at about 40 degrees north latitude, 18 degrees longitude. As the name suggests, arachnoids are circular to ovoid features with concentric rings and a complex network of fractures extending outward. In this image, the arachnoids range in size from approximately 50 kilometers (29.9 miles) to 230 kilometers (137.7 miles) in diameter. Since arachnoids are similar in form but generally smaller than coronae (circular volcanic structures surrounded by a set of ridges and grooves as well as radial lines), one theory concerning their origin is that they are a precursor to coronae formation. The radar-bright lines extending for many kilometers may have been caused by an upwelling of magma from the interior of the planet which pushed up the surface to form "cracks." Radar-bright lava flows are present in the central part of this image, also indicative of volcanic activity in this area. Some of the fractures cut across these flows, indicating that the flows occurred before the fractures appeared; such relations between different structures provides good relative age dating of events. At present, arachnoids are found only on Venus and can now be more closely studied with the high resolution (120 meter/0.07 mile) radar imagery from Magellan. ============================================================================ LAVINIA.TXT This is a Magellan full-resolution radar mosaic of the Lavinia region of Venus. The mosaic is centered at 50 degrees south latitude, 345 degrees east longitude, and spans 540 kilometers (338 miles) north to south and 900 kilometers (563 miles) east to west. As with all Magellan images acquired thus far, the illumination of the radar is from the left-hand side of the image. This area shows a diverse set of geologic features. The bright area running from the upper right to the lower left is interpreted as part of a belt of ridges, formed by compression and thickening of the upper layers of the planet. The areas between ridges suggest flooding by radar dark (and thus presumably) smoother lavas. The varied textures of the lavas can be seen in the mottled appearance of the plains which are cut by the ridges; brighter, rougher flows are also quite common. The particularly bright flows in the lower right corner are the northern extension of Mylitta Fluctus. The bright ridges adjacent to Mylitta Fluctus at the bottom center of the image also appear to have been affected by the volcanic activity. Some of these bright features have been interpreted as down-dropped areas roughly 5 kilometers (3 miles) wide. This would imply a region of extension where the crust has been pulled apart and thus was more easily flooded by the later lava flows. The thinner fractures running from the upper left seem to end at the ridge belt in the center of this mosaic. These thinner fractures are a continuation of a pattern seen throughout much of Lavinia and suggest a pattern of compression over a very large region. At the bottom of the image, overlying the ridges, is an impact crater 10-15 kilometers (6-10 miles) in diameter. The double or overlapped crater structure and asymmetrical ejecta pattern suggests that the incoming body broke up shortly before it hit, leaving closely-spaced craters. The placement of the crater on top of the ridges implies it is younger than the ridges; in fact, the crater may be one of the youngest features in this image. ___ _____ ___ /_ /| /____/ \ /_ /| Ron Baalke | baalke@mars.jpl.nasa.gov | | | | __ \ /| | | | Jet Propulsion Lab | Is it mind over matter, ___| | | | |__) |/ | | |___ M/S 301-355 | or matter over mind? /___| | | | ___/ | |/__ /| Pasadena, CA 91109 | Never mind. |_____|/ |_|/ |_____|/ | It doesn't matter.