Mars Craters
Spring 2003
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Mars Pathfinder landing site: Mars Pathfinder site, left:
April 1998; right: January 2000. An attempt to photograph the Pathfinder
site was made once before, in April 1998, by turning the entire MGS
spacecraft so that the camera could point at the known location of the
Mars Pathfinder lander. Turning the MGS spacecraft like this is not a
normal operation - it takes considerable planning, and disrupts the
ongoing, normal acquisition of science data. It took 3 attempts to
succeed, but on April 22, 1998, MOC acquired the picture seen on the left.
The three near-by major landmarks that were visible to the Pathfinder's
cameras are labeled here (North Peak, Big Crater, Twin Peaks). It was
known at the time that this image was not adequate to see the Pathfinder
lander because the camera was not in focus and had a resolution of only
3.3 meters (ll ft) per pixel. In this and all other images shown here,
north is up. All views of the 1998 MOC image are illuminated from the
lower right, all views of the 2000 MOC image are illuminated from the
lower left. |
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Layers & Boulders in Crater Wall: The high resolution
image was targeted on a 3 kilometers- (1.9 miles)- wide impact crater on
the floor of a larger crater in the Nepenthes Mensae region (near 3°S,
239°W). The crater is three times wider than the famous Meteor Crater
in northern Arizona, USA. The high resolution image shows many small
windblown drifts or dunes in the low areas both within the crater and
outside on the surrounding terrain. Some portions of the crater's walls
exhibit outcrops of bare, layered rock. Large boulders have been dislodged
from the walls and have tumbled down the slopes to the crater floor. Many
of these boulders are bigger than school buses and automobiles. |
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Fretted Terrain Crater: Some craters in the middle latitudes
of Mars exhibit strange, concentric- and radial-textured patterns on their
floors - as seen here. The origin is presently unknown. This crater is in
northern Arabia Terra, and the picture was taken in April 1998. |
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Martian Crater: This crater on northern Elysium Planitia is
a little more than twice the diameter of the famous Meteor Crater in
Arizona, U.S.A. It formed by the impact and subsequent explosion of a
meteorite. Picture from MOC in July 1998. |
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Pedestal Crater: The upper layer of the plains surrounding
this impact crater have been stripped and deflated by wind. The rocky
ejecta of the crater, however, protected the material beneath the ejecta
blanket from such erosion. This process also gives the ejecta deposit a
"raised relief" appearance. MOC image from July 6, 1998. |
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Detail of an Impact Crater, Acidalia Planitia: the eastern
third of a 4 kilometer-diameter impact crater located in Acidalia
Planitia. This image shows the walls, raised rim, and ejecta material
thrown out of the crater during this blast. Similar features are seen at
the famous Meteor Crater in northern Arizona, U.S.A. - except that this
Martian example is about 4 times larger than the one in North America. In
this example, faint radial and concentric ridges and cracksin the crater
ejecta are believed to arise from the motion of ejected material in a
manner similar to thick pancake batter flowing across the surface. The
crater is located at 34.3°N latitude, 42.9°W longitude. |
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The Geodesy Campaign: During May 1999, however, the Wide
Angle cameras are being used instead to map the whole planet at the
intrinsic resolution of the WA camera - 230 meters (750 feet) per pixel.
While the blue WA camera continues to capture the global map so that daily
weather can still be monitored, the other WA camera (with the red filter)
is building up swaths of full-resolution coverage. Geodesy is the
measurement of a planet's shape and the location of features on its
surface. The intent of the geodesy campaign is to acquire, during a short
period of time, simultaneous measurements by the Mars Orbiter Laser
Altimeter (MOLA), the Radio Science (RS) investigation, and the MOC. MOLA
observations provide precise, absolute measurements of a set of profiles
around the planet, but their spacing is quite large relative to their
resolution. RS measurements provide detailed information about the
position of the spacecraft, critical to processing both the MOC and MOLA
data. MOC provides both a higher resolution base map on which the other
data can be overlain and, using stereoscopic measurements, provides the
potential for a ten-fold improvement in the spatial resolution of the
topography. This image shows an example of such stereo from the Mare
Tyrrhenum region, centered at 27.3°S, 227.0°W (NOTE: Red-blue
glasses are needed to view the stereo effect). The crater that dominates
the center of Figure MOC2-127b is about 50 kilometers (31 miles)
across. |
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"Looking Into" Martian Craters - Tartarus Montes Region:
During the first week of May 1999, the Mars Orbiter Camera (MOC) spent
some time peering into Martian impact craters. This crater is located on a
plain west of the Tartarus Montes (east of Elysium Mons volcano). The
crater is about 2.7 kilometers (1.7 miles) across. Illumination is from
the left. If you have ever visited the famous Meteor Crater in northern
Arizona, U.S.A., then you are aware of its immense size on a human scale.
The Arizona crater, however, is only 1 kilometer across (0.62 miles),
whereas this crater is nearly three times that size. This crater was
formed by the impact and explosion of a meteorite at some time in the
Martian past. After the crater formed, it was modified by wind and
erosion. The crater shows deposits of sand and dust on the floor and in
low areas around the rim, also boulders and other debris that has slid
down the inside walls of the crater; and some crater walls show exposures
of bedrock. |
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"Looking Into" Martian Craters - Syria Planum Region:
During the first week of May 1999, the Mars Orbiter Camera (MOC) spent
some time peering into Martian impact craters. This crater is located in
south-central Syria Planum and is about 7.0 kilometers (4.4 miles) across.
Illumination is from the upper left. If you have ever visited the famous
Meteor Crater in northern Arizona, U.S.A., then you are aware of its
immense size on a human scale. The Arizona crater, however, is only 1
kilometer across (0.62 miles), whereas this crater is seven times wider.
This crater was formed by the impact and explosion of a meteorite at some
time in the Martian past. After the crater formed, it was modified by wind
and erosion. The crater shows deposits of sand and dust on the floor and
in low areas around the rim, also boulders and other debris that has slid
down the inside walls of the crater; and some crater walls show exposures
of bedrock. |
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"Looking Into" Martian Craters - Hesperia Planum Region:
During the first week of May 1999, the Mars Orbiter Camera (MOC) spent
some time peering into Martian impact craters. This crater is found on
Hesperia Planum and is 7.3 kilometers (4.5 miles) across. Illumination is
from the upper left. If you have ever visited the famous Meteor Crater in
northern Arizona, U.S.A., then you are aware of its immense size on a
human scale. The Arizona crater, however, is only 1 kilometer across (0.62
miles), whereas this crater is seven times wider. This crater was formed
by the impact and explosion of a meteorite at some time in the Martian
past. After the crater formed, it was modified by wind and erosion. The
crater shows deposits of sand and dust on the floor and in low areas
around the rim, also boulders and other debris that has slid down the
inside walls of the crater; and some crater walls show exposures of
bedrock. |
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Fluidized Crater Ejecta Deposit: The Mars Orbiter Camera
(MOC) onboard the Mars Global Surveyor (MGS) spacecraft continued to
obtain high resolution images of the red planet into August 1998. At this
time, each ground track (the portion of Mars available for MOC imaging on
a given orbit) covers areas from about 40°N on the late afternoon side
of the planet, up over the sunlit north polar cap, and down the early
morning side of Mars to about 20°N latitude. Early morning and late
afternoon views provide good shadowing to reveal subtle details on the
Martian surface. Views of Mars with such excellent lighting conditions
will not be seen by MOC once MGS's Science Phasing Orbits end in
mid-September 1998. The image shown here, MOC image 47903, was targeted on
Friday afternoon (PDT), August 7, 1998. This picture of ejecta from a
nameless 9.1 kilometer (5.7 mile)-diameter crater was designed to take
full advantage of the present lighting conditions. When the image was
taken (around 5:38 p.m. (PDT) on Saturday, August 8, 1998), the Sun had
just risen and was only about 6° above the eastern horizon. With the
Sun so low in the local sky, the contrast between sunlit and shadowed
surfaces allowed new, subtle details to be revealed on the surface of the
crater ejecta deposit. The crater shownhere has ejecta of a type that was
first identified in Mariner 9 and Viking Orbiter images as "fluidized
ejecta. Ejecta is the material that is thrown out from the crater during
the explosion that results when a meteor - piece of a comet or asteroid -
collides with the planet. Fluidized ejecta is characterized by its lobate
appearance, and sometimes by the presence of a ridge along the margin of
the ejecta deposit. In the case of the crater shown here, there are two
ridges that encircle the crater ejecta - this type of ejecta deposit is
sometimes called a double-lobe rampart deposit. The MOC image shows that
this particular crater also has "normal" ejecta that occurs out on the
plains, beyond the outermost ridge of the main, fluidized ejecta deposit.
Fluidized or "rampart" ejecta deposits have long been thought by many Mars
scientists to result from an impact into a surface that contains water.
The water would have been underground, and could have been frozen or
liquid. According to the prevailing model, when the meteor hit, this water
was released - along with tons of rock and debris - and the ejecta flowed
like mud. Images with resolutions higher than those presently attainable
from the 11.6 hr elliptical orbit are needed to see the specific features
(such as large boulders "rafted" by the dense mud) that would confirm or
refute this model. Such images may be acquired once MGS is in its mapping
orbit. |
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Small, Fresh Impact Crater With Dark Ejecta: this picture is
one of the first images obtained by MOC following the May 1998 period of
solar conjunction. During solar conjunction, MOC and the other instruments
on Mars Global Surveyor were off while Mars was behind the Sun, relative
to Earth. The spacecraft could not communicate with Earth during this
time. After solar conjunction, Mars Global Surveyor entered the SPO-2
observing phase - the second Science Phasing Orbit period. Orbit 338 was
the first orbit on which MOC obtained pictures following solar
conjunction. This orbit executed on June 1, 1998. The picture above shows
a 12.3 meters (40 feet) per pixel view of the floor of an ancient, eroded,
47 kilometer (29 miles) wide impact crater. The most striking feature in
this image is the small crater with dark ejecta on the far right side.
This crater, formed by a meteor impact, is only about 38 meters (125 feet)
across. The blast that formed the crater sent out ejecta in a radial
pattern around the impact site. The ejecta pattern may be dark because
subsurface dark material was thrown out by the impact or because the
disturbed ground reflects less light. By Martian standards, this crater is
quite young - so young that fine, bright dust has not yet covered it up.
While interpreted to be geologically young, the crater is definitely more
than 18 years old, because it is visible as a small, dark spot in the
Viking context image taken in 1980. Also visible in this image are some
small wind-blown dunes and many small mesas and buttes that probably
formed by erosion. The MOC image 33806 subframe is located at 9.94°N,
311.23°W, in the eastern Arabia Terra region of Mars. The picture was
taken at 8:15 a.m. PDT on June 1, 1998. |
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