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New MGS Image: "Giant Polygon" Troughs, Elysium Planitia


http://mars.jpl.nasa.gov/mgs/msss/camera/images/9_7_98_poly_rel/index.html

                            Mars Global Surveyor
                             Mars Orbiter Camera

              Mars Orbiter Camera (MOC) High Resolution Images
                             SPO-2 Observations:

                 "Giant Polygon" Troughs, Elysium Planitia



Mars Global Surveyor Mars Orbiter Camera Release:          MOC2-65a, -65b, -65c, -65d, -65e
Mars Global Surveyor Mars Orbiter Camera Image ID:         589099008.52706
                                                           P527-06


                                (A) [Image]

                            165 KByte GIF image

(A) Regional context of MOC image 52706. The large crater at the top center
is 8.3 kilometers (5.2 miles) in diameter. The white box, centered near
31.4°N, 245.8°W, indicates the location of the MOC image 52706 subframe.
This context image is a portion of Viking 1 orbiter image 538a25. This is a
Mercator projection, north is up, illumination is from the left.

                                (B) [Image]

                            145 KByte GIF image

(B) MOC image 52706 subframe shown at 40% of its original size. As shown
here, the picture has a resolution of 8.5 meters (28 feet) per pixel and
covers an area that is 3.4 kilometers (2.1 miles) on each side. North is
approximately up, illumination is from the left.

                                (C) [Image]

                            140 KByte GIF image

(C) Same MOC image 52706 subframe as in (B), above, but with two white boxes
that indicate the location of full-resolution subframes shown below. The
white box on the left indicates the image shown in (D), the white box on the
right indicates the picture in (E), below.

                                (D) [Image]

                             60 KByte GIF image

(D) Full-resolution subframe of MOC image 52706. The location of this image
is identified on the left side of (C), above. The image resolution is 3.4
meters (11 feet) per pixel. The region shown is 0.87 by 0.87 kilometers
(0.54 x 0.54 miles) in size. North is approximately up, illumination is from
the left.

                                (E) [Image]

                             60 KByte GIF image

(E) Full-resolution subframe of MOC image 52706. The location of this image
is identified on the right side of (C), above. The image resolution is 3.4
meters (11 feet) per pixel. The region shown is 0.87 by 0.87 kilometers
(0.54 x 0.54 miles) in size. North is approximately up, illumination is from
the left.

  You may need to adjust the images for the gamma of your monitor to insure
                               proper viewing.

  Note: This MOC image is made available in order to share with the public
  the excitement of new discoveries being made via the Mars Global Surveyor
  spacecraft. The image may be reproduced only if the image is credited to
     "Malin Space Science Systems/NASA". Release of this image does not
  constitute a release of scientific data. The image and its caption should
  not be referenced in the scientific literature. Full data releases to the
   scientific community are scheduled by the Mars Global Surveyor Project
  and NASA Planetary Data System. Typically, data will be released after a
                 6 month calibration and validation period.

  Click Here for more information on MGS data release and archiving plans.

                                   CAPTION

Mars Global Surveyor's Mars Orbiter Camera (MOC) continued to obtain images
of the red planet during August and into September 1998. MOC has seen many
features that address old questions and ideas about the geologic history of
Mars.

Among the geological features examined by MOC in recent weeks--the enigmatic
"Giant Polygons" on the martian northern plains. Figure (A), above, shows an
example of what the Viking Orbiters saw in the 1970s--huge cracks, some more
than 1 kilometer (0.62 miles) wide, arranged in a polygonal pattern that
outlined flat-lying areas sometimes 5 to 20 kilometers (3 to 12 miles)
across. Giant polygons are most common in parts of Utopia Planitia and
Acidalia Planitia, but there is also a cluster of them in the lowlands west
of the Elysium volcanoes, on Elysium Planitia. The Viking (A) and Mars
Global Surveyor ((B) through (E)) images shown here are from Elysium
Planitia.

The exact origin of the giant polygons has never been determined. At first
glance, they appear to resemble mud cracks that one might see on the surface
of a dried-up puddle, pond, or lake. However, mudcracks and the polygonal
patterns they create are small features--like the size of a human hand. The
giant polygons on Mars are big enough to hold the entire downtown area of a
moderate-sized city.

Mudcracks form by dessication--i.e., the removal of water by evaporation
(drying). Many ideas about the polygons on Mars have centered on the idea
that they are somehow related to the dessication of thick layers of wet
sediment--perhaps deposited by some of the giant floods that Mars is known
to have had. However, there has been considerable debate about whether the
polygons formed in lava instead of sediment. Cooling lava might also crack
and give the polygon texture, some have argued. Two observations have been
made--using Viking images--that constrain the types of origins that can be
proposed: (1) most of the "cracks" appear to be graben--down-dropped blocks
caused by faulting, and (2) some of the "cracks" appear to indicate the
outlines of buried craters. These observations suggest that whatever caused
the polygons, the process appears to be confined to material that has buried
older terrain.

The new MOC image shown here confirms the impression--from Viking
images--that the polygon cracks--troughs--are graben formed by faults.
Unfortunately, the image does not provide ample information to distinguish
between the various models for the origin of the polygons or the material in
which they occur. The images, however, do show features of interest. The
floors of the polygon troughs (see (D) and (E)) have bright, almost
evenly-spaced, windblown ripples or drifts. Similar drifts can also be seen
in and encroaching upon the surrounding, small impact craters. These drifts
attest to the movement of sediment on the surface, and their brightness and
shape suggests that they have not been active recently.

MOC image 52706 was taken at about 11:36 p.m. (PDT) on August 31, 1998,
during the 526th orbit of Mars Global Surveyor as the spacecraft was nearing
its 527th periapsis (closest point to the planet during the orbit).

  ------------------------------------------------------------------------

Malin Space Science Systems and the California Institute of Technology built
the MOC using spare hardware from the Mars Observer mission. MSSS operates
the camera from its facilities in San Diego, CA. The Jet Propulsion
Laboratory's Mars Surveyor Operations Project operates the Mars Global
Surveyor spacecraft with its industrial partner, Lockheed Martin
Astronautics, from facilities in Pasadena, CA and Denver, CO.

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