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.
