baalke@mars.jpl.nasa.gov (Ron Baalke) (03/01/91)
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.baalke@mars.jpl.nasa.gov (Ron Baalke) (03/14/91)
Archive-name: astro/magellan/magellan-images/1991-03-13
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@msen.com (Edward Vielmetti, MSEN)
===================
MAGELLAN IMAGES
March 13, 1991
===================
I've placed two more Magellan images in VICAR format and 11 in GIF format
at the Ames SPACE archives, bringing the Magellan total to 14 VICAR images and
28 GIF images. They can be obtained 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. The two new VICAR files are called pancakes.img and bahet.img.
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 two 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/IMDISP directory. The VICAR format is the format used by the Image
Processing Lab (MIPL) at JPL. Most of the VICAR images are in 1024x1024
pixel resolution and are 1MB in size.
The pancakes.img image is the image showing the 7 pancake volcanoes.
The pan10.img file that I had uploaded earlier shows 3 of the 7 volcanoes.
I've converted all of the Magellan VICAR images into GIF format in 640x480
resolution. The new GIF files are:
saca1.gif pancakes.gif
saca2.gif pancake1.gif
saca3.gif bahet.gif
saca4.gif bahet1.gif
saca5.gif bahet2.gif
saca6.gif
The saca GIFs were all derived from the original saca.img file which I
placed at the Ames site earlier. The original file is quite large at
2.8 MB. This saca.img file had to be reduced by a factor of 4 in order for
it to fit in the 640x480 GIF resolution. The six new saca GIF files are
closeups of various parts of the saca.img with no detail loss. The
pancakes.gif was converted from pancakes.img, with pancake1.gif zooming
in on 4 of the volcanoes. Likewise, bahet.gif was converted from bahet.img,
with bahet1.gif and bahet2.gif being subsections of bahet.img, showing it in
greater detail.
============================================================================
PANCAKES.TXT (same as PAN10.TXT)
This image of the eastern edge of Alpha Regio, 30 degrees
south latitude, 11.8 east longitude, was acquired on November 7,
1990. It shows seven circular domical hills averaging 25
kilometers (15 miles) in diameter and maximum heights of 750 meters
(2475 feet). These features can be interpreted as 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 pattern on their surfaces suggests
if they are extrusive that a chilled outer layer formed then
further intrusion in the interior stretched the surface. The domes
may be analogous to volcanic domes on Earth. An alternative
interpretation is that the domes are the result of shallow
intrusions up-doming the surface layers. If they are intrusive,
then magma withdrawal near the end of the eruptions then produced
the fractures. The bright margins possibly indicate the presence
of rock debris or talus at the slopes of the domes. Fractures on
the surrounding plains are both older and younger than the domical
hills. Resolution of the Magellan data is about 120 meters (400
feet).
============================================================================
BAHET.TXT
This mosaic of Magellan data in the Fortuna region of Venus,
centered at 49 degrees north latitude, 2 degrees longitude, shows
two coronae. Coronae are large circular or oval structures first
identified in Soviet radar images of Venus. The structure on the
left, Bahet Corona, is about 230 kilometers (138 miles) long and
150 kilometers (90 miles) across. A portion of Onatah Corona,
over 350 kilometers (210 miles) in diameter, can be seen on the
right of the mosaic. Both features are surrounded by a ring of
ridges and troughs, which in places cut more radially-oriented
fractures. The centers of the features also contain radial
fractures as well as volcanic domes and flows. Coronae are
thought to form due to the upwelling of hot material from deep in
the interior of Venus. The two coronae may have formed at the
same time over a single upwelling, or may indicate movement of
the upwelling or the upper layers of the planet to the west over
time. A 'pancake' dome, similar to low-relief domes see in the
southern hemisphere, is located just to the southwest of Bahet.
Resolution of the Magellan data is about 120 meters (400 feet).
___ _____ ___
/_ /| /____/ \ /_ /| Ron Baalke | baalke@mars.jpl.nasa.gov
| | | | __ \ /| | | | Jet Propulsion Lab |
___| | | | |__) |/ | | |___ M/S 301-355 | Change is constant.
/___| | | | ___/ | |/__ /| Pasadena, CA 91109 |
|_____|/ |_|/ |_____|/ | baalke@mars.jpl.nasa.gov (Ron Baalke) (03/26/91)
Archive-name: astro/magellan/magellan-images/1991-03-25
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@msen.com (Edward Vielmetti, MSEN)
===================
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 |
|_____|/ |_|/ |_____|/ |