Introduction to Mars

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Introduction to Mars Part Three
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Bright areas are are thought to be rich in
heavily oxidized iron minerals (Fe3, like in
hematite) and dark areas contain un-oxidized iron
bearing minerals (Fe2, like olivine and
pyroxene).
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Datum
Since Mars has no oceans and hence no 'sea
level', a zero-elevation surface or mean gravity
surface must be selected. Zero altitude (datum)
is defined by the 610.5 Pa (6.105 mbar)
atmospheric pressure surface (approximately 0.6
of Earth's) at a temperature of 273.16 K. This
pressure and temperature correspond to the triple
point of water.
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Northern Hemisphere
At high northern latitudes, most of the plains
are at elevations of 1-2 km below the datum. The
cause of the dichotomy between cratered uplands
and low-lying plains is unknown. Could ocean
floor spreading have formed the low-lying plains
like in Earths ocean basins? More favored is
the idea that the low-lying plains lie within the
remnant of an enormous impact basin that formed
at the end of planetary accretion.
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Southern Highlands
The southern hemisphere of Mars is predominantly
ancient cratered highlands somewhat similar to
the Moon.
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Southern Hemisphere
 The physiography of the surface has a marked
north-south asymmetry. Much of the southern
hemisphere is covered with heavily cratered
terrain, and a large lobe of cratered terrain
extends into the northern hemisphere between
longitudes 30W and 280W. This terrain clearly
dates from early in the planet's history, when
impact rates were much higher than subsequently.
By analogy with the Moon, the terrain is believed
to have formed prior to 3.8 billion years ago.
The 4.5-billion-year-old Martian meteorite
ALH84001 is presumably from this terrain. Most of
the cratered terrain stands at elevations of 1-4
km above the Mars datum.
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Hellas Basin
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Hellas Planitia, also known as the Hellas Impact
Basin, is a roughly circular impact crater
located in the southern hemisphere. With a
diameter of about 2,100 km (1304 Miles), it is
the largest impact structure on the planet. The
basin is thought to have been formed during the
heavy bombardment period of the Solar System,
about 3.9 billion years ago, when a large
asteroid impacted Mars.
The altitude difference between the rim and the
bottom is 9 km (5.6 Miles). The depth of the
crater (4 km (2.4 Miles) below the topographic
datum, or "sea level" of Mars) explains the
atmospheric pressure at the bottom 840 Pa (8.4
mbar) (.25 InHg) (. This is 38 higher than the
pressure at the topographical datum (610 Pa, or
6.1 mbar or .18 InHg). The pressure is high
enough that water is speculated to be present in
its liquid phase at temperatures slightly above 0
C (32 F).
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Lunar South Pole Aitken Basin (Giant South
Polar Basin)

• Very Large (d2500 km) and Very Old (gt4 Ga)
• Deep-seated Mantle as clasts within breccias and
  impact melt.
• Old basalts derived from different mantle
  composition.
• Old highland rock not modified by younger impact
  basin.
• Away from influence of areas of moon rich in U,
  Th, K, REE.

• Far removed from other sampled sites on moon
  Different rock types?

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At 4,500 km long, 200 km wide and 11 km deep, the
Valles Marineris rift system is ten times longer,
seven times wider and seven times deeper than the
Grand Canyon of Arizona, making it the largest
known crevice in the solar system.
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This image, taken by the High Resolution Stereo
Camera (HRSC) on board ESA's Mars Express
spacecraft, shows the central part of the
4000-kilometer long Valles Marineris canyon on
Mars. The HRSC obtained the image during orbits
334 and 360 with a resolution of approximately 21
meters per pixel for the earlier orbit and 30
meters per pixel for the latter. The scene
shows an area of approximately 300 by 600
kilometers and is taken from an image mosaic that
was created from the two orbit sequences. The
area is located between 3 to 13  South, and
284 to 289 East.
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This image, taken by the High Resolution Stereo
Camera (HRSC) on board ESA's Mars Express
spacecraft, shows part of Tithonium Chasma, a
major trough at the western end of the Valles
Marineris canyon on Mars.
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The image shows the western end of the canyons
Tithonium Chasma and Ius Chasma, part of the
Valles Marineris canyon system, which are up to
5.5 kilometres deep.
The canyon floors are covered by a dark, layered
material, the "Interior Layered Deposits". These
deposits are marked by a system of polygonal
cracks through which the underlying,
lighter-colored rock can be seen. The Interior
Layered Deposits are still a major topic of
research. Parts of the deposits are most probably
volcanic, while in other areas a sedimentary
origin has been proposed. The morphology of the
valley flanks has been modified by "slumping" and
rockfalls. Some of the major slumps here are more
than thirty kilometers wide.
The large, deeply eroded Crater Oudemans in the
south of the area (bottom of the image) has a
diameter of about 120 kilometers. Around the
central mount of the crater, large plains
composed of dark rock can be seen. These plains
are covered by lighter sediments, deposited
through the action of the wind.
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How Did Valles Marineris Form?
Most researchers agree that Valles Marineris is a
large tectonic "crack" in the Martian crust,
forming as the planet cooled, affected by the
rising crust in the Tharsis region to the west,
and subsequently widened by erosional forces.
However, near the eastern flanks of the rift
there appear to be some channels that may have
been formed by water or carbon dioxide
The most agreed upon theory today is that the
Valles Marineris was formed by rift faults like
the East African Rift Valley, later made bigger
by erosion and collapsing of the rift walls. One
source of this erosion, proposed by Nick Hoffman
is decompression of the Noctis Labyrinthus carbon
dioxide aquifer. As carbon dioxide is
decompressed it turns from a solid to a fluid/gas
and can travel at great velocities through the
thin atmosphere of Mars.
Because the Valles Marineris is thought to be a
large rift valley, its formation is closely tied
with the formation of the Tharsis Bulge. The
Tharsis Bulge was formed from the Noachian to
Late Hesperian period of Mars.
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The geologic history of the central canyon system
is complex first the surface collapsed into a
few deep depressions that later became filled
with layered material, perhaps as lake deposits.
Then graben-forming faults cut across some of the
older troughs thus widening existing troughs,
breaching barriers between troughs, and forming
additional ones. At that time the interior
deposits were locally bent and tilted, and
perhaps water, if still present, spilled out and
flowed toward the outflow channels. Huge
landslides fell into the voids created by the new
grabens. Wind-drifted material, mostly dark in
color, apparently still moves along the canyon
floor and locally forms conspicuous dunes.
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Surface Water
Although liquid water is currently unstable on
the surface of Mars, theoretical studies indicate
that flowing groundwater might be able to form
valley networks if the water flowed beneath a
protective cover of ice. Alternatively, because
the valley networks are confined to relatively
old regions of Mars, their presence may indicate
that Mars once possessed a warmer and wetter
climate in its early history.
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Surface Water
Ravi Vallis is a 300-kilometer (186-mile) long
channel. Like many other channels that empty into
the northern plains of Mars, Ravi Vallis
orginates in a region of collapsed and disrupted
("chaotic") terrain within the planet's older,
cratered highlands. Structures in these channels
indicate that they were carved by liquid water
moving at high flow rates.
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Surface Water
Near Ares Vallis in Chryse Planitia streamlined
islands that formed by water that flowed south to
north.
The height of the scarp surrounding the upper
island is about 400 meters (1,300 feet), the
southern island is about 600 meters (2,000 feet)
high.
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Evidence for Recent Liquid Water on Mars
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Kasei Valles, one of the largest outflow channels
on Mars.
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Early Faint Sun Dilemma (Kasting, 1982)
Stars like the sun increase their luminosity
through time as the hydrogen in the star's core
is converted to helium. Estimates have the Suns
luminosity 25 fainter 4 billion years ago. Thus
one could argue that Venus, not Earth or Mars was
in the habitable zone 4 billion years ago and
that Venus could have been a life-bearing
planet. Changes in greenhouse warming of a
planets surface can counteract the faint sun
effect. An early blanketing atmosphere could have
given Mars a wetter warmer climate in the past.
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Pavonis Mons Glacial Ridges?
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Icy Ejecta Blanket?
This image, taken by the High Resolution Stereo
Camera (HRSC) on board ESA's Mars Express
spacecraft, shows a detail of the Medusa Fossae
formation. An impact crater is the youngest
feature of the stratigraphic sequence (layers of
rocks produced over time) that can be observed in
this image. This crater has a well-preserved
ejecta blanket with a lobate (lobe-like)
appearance, which is believed to indicate the
presence of water or water ice in the impacted
target. As a crater forms on a flat surface, it
expands in a circular fashion.
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Mars Obliquity and Climate Change
Where is the best place on Mars to look for
evidence of life? At the poles, say some
scientists. Although frozen solid today, in past
eras, when Mars was more highly tilted, the poles
were warm enough for liquid water to form.
At present the Mars obliquity is similar to the
Earth's. Yet while the Earth experiences only
minor changes in obliquity, the obliquity of Mars
changes chaotically. It ranges mostly between 15
and 35, but may occasionally reach 60. Summer
temperatures at the poles change dramatically
during the obliquity cycle, being much warmer at
high obliquities than at low obliquities
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Mars Atmosphere
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Martian Clouds
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No Plate Tectonics, No Greenhouse Effect on Mars
Early in its history, Mars may have been much
more like Earth. As with Earth, perhaps almost
all of its carbon dioxide was used up to form
carbonate rocks. But lacking the Earth's plate
tectonics, Mars is unable to recycle any of this
carbon dioxide back into its atmosphere and so
cannot sustain a significant greenhouse effect.
The surface of Mars is therefore much colder than
the Earth would be at that distance from the Sun.

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Martian Dust Storms
Localized tropical dust storms occur on Mars
during all seasons. A typical storm is about 1
million km2 size and comprises microscopic
particles which move with speeds of 15-30 m/s
(33--66 mph) before dissipating after a few days.
Dust devils, about 2 km width and a few
kilometers high, have also been observed in the
tropics by the Viking orbiters. However, the most
dramatic aspect of the Martian climate is when a
dust storm expands to encompass nearly one or
both hemispheres. Indeed, sometimes these great
dust storms can become completely global.
Advancing dust storm front from MGS August 9,
1999
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Dust Storms
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Dust Devils
At the center right of this image (above left) is
a dust devil that, on May 21, 2002, was seen
climbing the wall of a crater in western Terra
Meridiani. The dust devil was moving toward the
northeast (upper right), leaving behind a dark
trail where a thin coating of surficial dust was
removed or disrupted as the dust devil advanced.
Dust devils most commonly form after noon on days
when the martian air is still.
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Martian Dunes
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This image, taken by the High Resolution Stereo
Camera (HRSC) on board ESAs Mars Express
spacecraft, shows a detail of the Medusa Fossae
formation. The Amazonis Sulci, with its ridges
and grooves, appears to be wind-sculpted. The
lack of craters superposing this surface
indicates that wind erosion has been the latest
stage of eroding processes acting here.
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Vital statistics for Phobos and Deimos
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Phobos
Phobos is the larger and innermost of Mars' two
moons. Phobos is closer to its primary than any
other moon in the solar system, less than 6000 km
above the surface of Mars. It is also one of the
smallest moons in the solar system. Diameter
22.2 km (27 x 21.6 x 18.8)
Phobos is doomed because its orbit is below
synchronous altitude and tidal forces are
lowering its orbit (current rate about 1.8
meters per century). In about 50 million years it
will either crash onto the surface of Mars or
(more likely) break up into a ring. (This is the
opposite effect to that operating to raise the
orbit of the Moon.)
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Deimos
One idea is that Phobos and Deimos, Mars's other
moon, are captured asteroids.
However, there are other ideas about the origin
of Mars's moons. One, favored by Duxbury, is that
they are lightly accumulated ejecta from asteroid
impacts on the Martian surface, with Phobos
composed of ejecta orbiting Mars faster than the
planet rotates and Deimos, whose orbit is
further out and orbital motion slower, composed
of ejecta orbiting more slowly than the planet
rotates.