Mars 1
Data
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Name – The planet Mars was named for the Roman god of war because of its
distinctive blood-red color when observed in the sky.
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Location – Mars is the fourth planet from the Sun, with an average distance of
approximately 142 million miles.
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Size 2 – Mars measures 4217 miles in diameter. The surface area of Mars is almost
equal to that of the continents of the Earth.
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Rotational Period – 1.03 days. The day on Mars is approximately 37 minutes longer
than the day on Earth.
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Orbital period – 1.88 years (687 days).
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Inclination of Rotation Axis – Mars’ rotation axis is inclined by 25.2, which, like
Earth, causes it to undergo seasonal changes. However, because the Martian orbit
is larger than Earth’s, seasons on Mars are about twice as long.
Orbital Eccentricity – The orbit of Mars displays a high orbital eccentricity
(0.093). This high orbital eccentricity of Mars plays a role in seasonal changes.
Number of Satellites – 2.
Atmosphere 3
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Composition – Mars’ atmosphere is composed of 95.4% carbon dioxide (CO2), 2.7%
nitrogen (N2), 0.13% oxygen (O2), and 0.03% water vapor (H2O). The abundance of
water vapor in the Martian atmosphere varies with season and location.
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Pressure – The Martian atmosphere is substantially less massive than the Earth’s
atmosphere. Atmospheric surface pressure on Mars is 0.006 bars (approximately
1/150 the sea-level pressure on Earth).
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Percentage Not Quantity – Note that the percentage of carbon dioxide in the
Martian atmosphere is about the same as Venus. However, this does not mean
that there is the same quantity of carbon dioxide in the atmospheres of these two
planets. Venus has a significantly greater amount of carbon dioxide in its
atmosphere as is reflected by its high atmospheric surface pressure (92 bars).
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Temperature – Because of the low mass of the Martian atmosphere and the planet’s
greater distance from the Sun, the air temperature on Mars is colder than the Earth. It
ranges from about -20º F during daytime in the summer to about -150º F during
nighttime.
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Global Circulation 4 – Atmospheric circulation on Mars is primarily associated with
the exchange of carbon dioxide between the atmosphere and the polar caps. This
exchange is caused by the changing of the seasons. In the summer (northern or
southern hemisphere), an enormous amount of frozen carbon dioxide associated with
the polar cap evaporates, adding large amounts of carbon dioxide gas to the Martian
atmosphere. Conversely, in the winter, carbon dioxide gas within the atmosphere of
Mars freezes onto the polar cap. This transference of carbon dioxide causes
atmospheric pressure on Mars to vary by 25%, and thereby generating strong winds
(up to 250 miles/hour) and global circulation. (On Earth, severe storms may cause a
pressure variation of only a few percent.)
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Clouds 5 – Clouds on Mars are usually found around high volcanoes. As air rises
over a Martian volcano, the cooler temperature causes the water vapor to condense
and form clouds. This process is called the orographic effect. (On Earth, the
orographic effect is often associated with mountains.)
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Dust Devils – The dry air of Mars and the significant day-night temperature
differences can lead to the formation of small cyclonic storms called dust devils,
which are common in Earth’s deserts. The rover Spirit has imaged several dust
devils 6.
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Global Dust Storms 7 – In the southern hemisphere during the summer, Martian
weather conditions can become unstable causing a large quantity of surface dust to be
raised (perhaps by dust devils) within the Martian atmosphere. These dust clouds can
spread until nearly the entire planet is shrouded. It takes about one quarter of the
Martian year (six Earth months) for the dust to settle.
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Evolution – Like Earth, the atmosphere of Mars was formed from volcanic
outgassing. Large amounts of nitrogen, carbon dioxide and water vapor were
released to produce a dense atmosphere. Evidence suggests that atmospheric pressure
on Mars was twice the sea-level pressure of the Earth’s atmosphere. This substantial
atmosphere generated a greenhouse effect, which lead to a surface temperature above
32º F. These conditions allowed for the existence of liquid water on the surface of
Mars. However, what happen to this early atmosphere, causing it to “thin” to its
present state? Possible causes for the depletion of the thicker Martian atmosphere
include: (1) gradual erosion of the atmosphere by solar wind, possibly helped by
irregularities in the planet’s magnetic field, (2) impact by a body large enough to
blow away a significant percentage of the atmosphere, and (3) Mars’s low gravity
allowing the atmosphere to escape into space.
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Surface
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Hydrosphere – Mars used to be a very wet place. A number of clues remain from that
earlier time, indicating that Mars was perhaps once host to great rivers, lakes and
perhaps even an ocean. However, because of the extreme decrease in atmospheric
pressure, liquid water can no longer exist on the surface of Mars. At 0.006 bars,
water boils at 32º F, which is also its freezing point. Like carbon dioxide, water goes
directly from a solid (ice) to a gas (water vapor), without ever becoming a liquid; a
process referred to as sublimation.
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Mineralogical Clues – A detailed analysis of Martian minerals is necessary to
understand the history of water on Mars. NASA’s Opportunity and Spirit rovers
found evidence of hydrated minerals and erosional and depositional features
indicating an ancient wet environment.
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Sulfate Salts – Spectral analysis of outcropping of rocks shows evidence of
significant amounts of sulfate salts. On Earth, rocks containing so much salt
either formed in water or, after formation, were soaked in water for a
prolonged period of time.
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Blueberries 8 – Images have revealed spheres the size of BBs embedded in
outcrop rocks. Researchers call them “blueberries”, though they are actually
gray in color. These blueberries are probably what geologists call
“concretions” that formed when water deposited layer after layer of an ironrich mineral called hematite around tiny grains of sand.
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Vugs – Images of an outcrop of rock show many thin, flat holes about the size
of pennies. These holes, or “vugs”, match the distinctive appearance of Earthrock vugs that form where crystals of salt minerals grow inside rocks that sit
in briny water then disappear by eroding or dissolving.
Where Is It? – At present, the water on Mars exists in three places:
1. Water Vapor – Water vapor in the Martian atmosphere is continually being
destroyed. Solar ultraviolet light breaks apart water molecules; a process
called photo-dissociation. The hydrogen then escapes into space and the
oxygen remains behind.
2. Polar Ice – A portion of the Martian polar caps are composed of water-ice.
Particularly, the northern cap during the summer displays direct evidence of
water ice. Because of the warmer temperature, the carbon dioxide ice easily
evaporates exposing the water-ice portion referred to as a residual cap. This
residual cap may be one of the main storage areas of water on Mars.
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Proof 9 – Images acquired by NASA’s Phoenix Mars Lander show dicesized lumps of ice sublimating over the course of four days. The ice was
excavated by Phoenix’s robotic arm in a trench informally named “DodoGoldilocks”.
3. Permafrost – In certain areas of Mars, water ice is mixed in with the surface
material. This mixture of ice and “soil” is called permafrost.
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Importance – The reason for the intense interest in Martian water is simple:
Without water, there can be no life as we know it. If life ever existed (or does
exist) on Mars, it did so in the presence of a long-standing supply of water.
Therefore to find evidence of this life, it is necessary to search where liquid water
was once stable and below the surface where it still might exist today.
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Surface Elevations – The tallest geologic feature on Mars is the volcano Olympus
Mons, rising about 15.5 miles above the surrounding plains. In comparison, the
tallest mountain on Earth, Mount Everest, is about 5.5 miles above sea level. Overall,
the heights of geologic features on Mars are greater than those on Earth. The reason
for the extreme difference in surface elevations on Mars and the Earth relates to the
difference in their surface gravity. Mars’ surface gravity is two-fifths that of Earth,
and therefore a geologic feature such as a volcano can rise to a much greater height
before it begins to subside under its own weight.
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Terrains 10 – The most conspicuous feature of Mars is a sharp contrast (known as the
Martian dichotomy) between the highlands of the southern hemisphere and the
lowlands of the northern hemisphere. Although there several hypotheses, the most
favorable to explain this dichotomy is that the northern hemisphere was struck by an
object at least 1,000 miles in diameter about four billion years ago. If so, this would
be the largest impact in the solar system.
1. Highlands – The highlands lie 0.5 to 2.5 miles above the average surface level.
They are characterized by a high abundance of large craters, indicating that little
geologic activity has occurred. The origin of these craters is most likely the
prolonged period of heavy meteoritic bombardment ending around 3.8 billion
years ago (the same event that formed the lunar highlands). However, the
highlands of the Moon and Mars display differences: (1) Martian craters tend to
be more degraded, indicating a higher erosion rate early in the planet’s history, (2)
runoff channels are common throughout the Martian highlands, and (3) smooth
areas lie between the craters of the Martian highlands. These areas most likely
originate from volcanic lava flows and other forms of deposition.
2. Lowlands – The lowlands are mostly well below the average surface level, except
in the volcanic regions of Tharsis and Elysium. The low crater density indicates
geologic activity. Many lava flows and wrinkled ridges are evident, indicative of
volcanism. Also, strange patterns of wrinkles, cracks, low ridges and polygon
fractures are observed, possibly suggesting processes associated with wind and
ice. (Similar polygon fractures are found in arctic soils on Earth, known as
patterned ground.)
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Tharsis Region – The Tharsis region is a volcanically formed region about the
size of North America. It rises about 6 miles above the average surface level.
The origin of the Tharsis region is associated with two processes: (1) the
accumulation of lava flows over billions of years and (2) an upwelling plume
(hot spot) causing the crust to be uplifted. The uplifting causes fractures to
form within the crust 11.
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Elysium region – Like the Tharsis region, the Elysium province originated
from hot spot activity, but smaller in scale.
Features – Mars exhibits some surface features varying and unique to the planet.
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Craters – The surface of Mars is riddled with thousands of craters, concentrated
particularly in the southern hemisphere. They resemble craters observed on the
Moon and Mercury, but with some differences.
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Crater Density and Crater Definition – Unlike the surface of the Moon and
Mercury, the Martian surface has been subjected to significant erosion. At
present, the major agent of erosion on Mars is wind-blown dust. Like Earth,
wind-blown dust forms dunes on Mars 12. However, in Mars’ early history,
running water was also an effective erosional agent. When comparing craters
on Mars to those observed on the Moon and Mercury, the affects of erosion
are quite evident. Small-sized craters on Mars are less abundant and large
craters appear shallow and subdued. This degradation of Martian craters is
primarily due to the deposit of wind-blown dust, which completely covers the
smaller craters and partially covers the larger ones.
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Fluidized Ejecta (Splosh Craters) 13 – Unlike the rough, hilly ejecta blankets
of lunar and Mercurian craters, many Martian craters have smooth ejecta
blankets with well-defined edges. The most likely reason for this difference
lies in the presence of permafrost (ground ice) on Mars. The heat generated
by the impact temporarily melts the permafrost, causing the ejecta material to
flow along the ground.
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Impact Basins – Mars exhibits fewer impact basins than the Moon. The most
likely explanation is that many of the basins that formed early in Martian history
have been degraded by erosional and geologic activity. The Argyre Basin is the
best-preserved impact basin on Mars, measuring about 425 miles in diameter 14.
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Volcanoes – Hundreds of volcanoes have been identified by high-resolution probe
surveys of the surface of Mars. Most of the large Martian volcanoes are located
in the Tharsis and Elysium regions. These volcanoes are similar in structure to
shield volcanoes found in Hawaii. (A shield volcano is a broad, gently sloping
cone, constructed of solidified lava flows. The eruptions are mostly quiet with
large basaltic lava flows of low viscosity.)
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Olympus Mons 15, 16 – Olympus Mons is the largest volcano on Mars (or any
other planet). It measures approximately 425 miles in diameter and rises 15.5
miles above the surrounding plains. The volcano is also characterized by a
caldera 50 miles wide. (A caldera is a basin-like depression; the remnant of
the opening (vent) through which an eruption takes place.)
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Why So Large? 17 – Martian volcanoes are much larger than volcanoes on
Earth. Why? Volcanoes on Mars originate from hot spot activity. Because of
the lack of plate tectonic motion on Mars, a hot spot remains fixed under a
specific region of the planet’s crust 18. Therefore over billion of years, the
accumulation of many lava eruptions produces a large volcano.
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Canyons 19 – Dominating the equatorial region of Mars is a large system of
canyons, known collectively as Valles Marineris (Mariner Valley). Mariner
Valley measures approximately 2,500 miles in length, and in areas, approximately
350 miles wide and 4 miles deep 20. Martian canyons are huge cracks in the
planet’s crust, formed by tectonic processes, and subsequently widened by the
effects of erosion 21.
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Activity – There is no evidence of present-day volcanic activity. However,
crater densities suggest that particular volcanoes have been active within the
past few hundred million years. In fact, the youngest lava flows on Olympus
Mons are less than 100 million years old. This is a short time on the scale of
planetary history, and therefore it is possible that volcanic eruptions can occur
in the future.
Plate Tectonics – It is thought that Valles Marineris represents an ancient plate
boundary. Paleomagnetism of magnetized minerals on Mars have properties
similar to the alternating bands found on the ocean floors of Earth. One
theory proposes that these bands demonstrate plate tectonics four billion years
ago, before the planetary dynamo ceased.
Channels – There are two main types of channels on Mars:
1. Runoff Channels 22 – Like river valleys on Earth, Martian runoff channels
most likely formed by water flowing across the planet’s surface, originating
from underground springs and the drainage of rainfall. They have the
characteristic form of terrestrial river systems, with small tributary channels
merging into larger channels. These channels are located in the heavily
cratered highlands of the southern hemisphere, dating their formation and
activity around 3.8 billion years ago; a time when Mars had a thicker, warmer
atmosphere, allowing for the presence of liquid water.
2. Outflow Channels 23 – Outflow channels on Mars appear to originate from
sudden outpourings of tremendous amounts of underground water (floods).
Located within the equatorial region, these channels are vast in size,
measuring 5 miles or more in width and hundreds of miles long. At the head
of each outflow channel are jumbled masses of rock referred to as chaotic
terrain. This terrain is thought to have been created by the local collapse of
the Martian crust associated with the release of water. The mechanism
causing the outpouring of water is uncertain. However, the melting of
subsurface ice by volcanic activity and the uplift of the Tharsis region are
possible sources.
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Polar Caps 24 – The polar caps of Mars are easily observed through a moderately
sized telescope. They have been determined to be composed of about 70% water
ice and 30% carbon dioxide ice (dry ice).
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Seasonal Changes 25 – Like the Earth’s polar caps, the polar caps of Mars
increase and decrease in size with changing seasons. However, because of
Mars’ high orbital eccentricity, the planet is significantly farther out during
the southern hemisphere winter, resulting in a colder and longer winter, and
therefore generating a larger seasonal polar cap 26.
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Residual Polar Caps 27 – The northern polar cap and in turn the southern polar
cap shrinks, due to the evaporation of ice during the spring and summer
seasons. The remaining portion is referred to as a residual polar cap. Both the
northern and southern residual caps show spiral patterns of dark lanes in the
bright ice. These dark lanes are exposed areas of the Martian surface (slopes
and valleys), sufficiently heated to lose their ice cover. However, whereas the
southern residual polar cap is comprised of frozen carbon dioxide and waterice, the northern residual polar cap is solely composed of water-ice. This
difference is most likely related to deposits of dust (derived from the global
dust storms) on the northern polar cap during its growth in the winter. This
dust allows for a greater absorption of solar radiation during the spring and
summer, causing the northern cap to reach a high enough temperature to
evaporate all the frozen carbon dioxide and even a portion of the water-ice.
Surface Material 28 – The surface of Mars is primarily composed of fine-grained
particles (dust and sand) of silicate material. The planet’s reddish color is due to iron
oxide (rust) mixed in with this material. Because of winds associated with seasonal
circulation patterns, the fine-grained material is redistributed over the planet’s
surface, alternately exposing and covering the darker underlying terrain. This
seasonal change of surface markings was once thought to be related to biological
activity.
Interior
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Composition and Structure 29 – The average density of Mars is 3.94 g/cm3, indicating
a low abundance of metals (in other words, a larger quantity of silicate material).
Probes have shown evidence of a core. However, unlike the Earth’s metallic ironnickel core, Mars’ core is thought to be composed of iron sulfide (a lower density
material). Mars’ internal structure is differentiated into a crust, mantle and core.
However, because of the substantial amount of iron oxide associated with the planet’s
surface, the planet is not completely differentiated. Because of the lack of seismic
data, little is known about the properties of these layers.
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Magnetic Field –An important property for the formation of a substantial planetary
magnetic field is a liquid metallic core. Calculations suggest that the core of Mars is
solid, so it is not surprising that the planet lacks a strong magnetic field. However,
the Global Surveyor spacecraft discovered weak magnetic fields associated with
isolated areas of the planet’s surface. Apparently, Mars produced a planetary
magnetic field in its early history and the ancient rocks of these regions retained that
magnetism.
Life
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Misinterpretations – In 1877, the Italian astronomer Giovanni Schiaparelli recorded
linear markings he called canali or channels (later shown to be an optical illusion).
In English-speaking countries, the word canali was translated as canals, a term
suggesting construction by intelligent beings. Moreover, many 20th century observers
saw changes in the dark surface markings that seemed to be seasonal. Often the
regions darkened in the summer, as might be expected if plants were growing.
Although we now know for certain that intelligent beings or even large-scale life
forms on Mars do not exist, the possibility of life on Mars has been an intriguing
concept. In fact, the idea of “Martians” has become part of our culture 30.
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Results of Viking Landers 31 – In 1976, the Viking Landers performed a number of
experiments to detect evidence of life within the Martian soil. Although, the results
were negative, a final conclusion about the presence of life on Mars cannot be
determined from just one study. As stated earlier, an important factor for continued
study is the presence of water. This in itself maintains Mars as a strong candidate for
existing or fossil microbial life.
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ALH 84001 Meteorite 32 – Recent evidence of possible life on Mars is associated with
rocks found on Earth that came from Mars (meteorites). A particular meteorite
referred to as ALH 84001 (named this because it was found in the Allan Hills of
Antarctica in 1984) contains tiny clumps of rounded and elongated structures that
have been claimed to be fossils of long-dead Martian microbes 33. Further evidence
found within the meteorite is magnetite crystals known to be produced by terrestrial
bacteria. However, alternative explanations have been suggested that strongly
support a non-biological origin for these features.
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Origin – How did Martian rocks end up on Earth? One or more large impacts
caused some of Mars’ crustal material to be ejected out into space and eventually
land on Earth as meteorites. Confirmation of their origin comes from tiny bubbles
of gas preserved within the meteorite that match perfectly with the Martian
atmosphere.
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Methane – The Curiosity Rover 34 detected spikes in the level of methane in Mars’
atmosphere compared to the usual background readings. On Earth, most methane is
released by microbes that belch out the gas as they digest food. However, there is no
way to determine (currently) whether the methane spikes have a geological or
biological origin.
Moons
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Minor Moons – Mars has two small satellites called Phobos and Deimos. Because of
their small size (Phobos is about 17 miles long in its longest dimension and Deimos is
about 9 miles long in its longest dimension) 35, and therefore weak surface gravity,
the shapes are irregular.
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Surface Features and Composition – The surface features of Phobos and Deimos
are similar. They are both heavily cratered worlds composed of carbonaceous
material (the composition of C-type asteroids) and possibly some water-ice deep
in their interiors. The most impressive surface feature is a 6-mile-wide crater
called Stickney on Phobos 36. This impact caused fracturing of the moon’s crust,
observed as grooves hundreds of feet wide and 50 to 100 feet deep.
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Origin – Because Phobos and Deimos both have much in common with C-type
asteroids, both moons may be captured main-belt asteroids.
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Degrading Orbit – Phobos orbits only about 3700 miles from the surface of Mars.
Its orbit is gradually degrading, and is predicted that in 50 million years it will
collide with the planet or break up into a planetary ring.
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