Astronomy

Mars History Flash Presentation by JPL.

Mars is the fourth planet from the Sun and is commonly referred to as the Red Planet. The rocks, soil and sky have a red or pink hue. The distinct red color was observed by stargazers throughout history. It was given its name by the Romans in honor of their god of war. Other civilizations have had similar names. The ancient Egyptians named the planet Her Descher meaning the red one.

Before space exploration, Mars was considered the best candidate for harboring extraterrestrial life. Astronomers thought they saw straight lines crisscrossing its surface. This led to the popular belief that irrigation canals on the planet had been constructed by intelligent beings. In 1938, when Orson Welles broadcasted a radio drama based on the science fiction classic War of the Worlds by H.G. Wells, enough people believed in the tale of invading Martians to cause a near panic.

Another reason for scientists to expect life on Mars had to do with the apparent seasonal color changes on the planet’s surface. This phenomenon led to speculation that conditions might support a bloom of Martian vegetation during the warmer months and cause plant life to become dormant during colder periods.

In July of 1965, Mariner 4, transmitted 22 close-up pictures of Mars. All that was revealed was a surface containing many craters and naturally occurring channels but no evidence of artificial canals or flowing water. Finally, in July and September 1976, Viking Landers 1 and 2 touched down on the surface of Mars. The three biology experiments aboard the landers discovered unexpected and enigmatic chemical activity in the Martian soil, but provided no clear evidence for the presence of living microorganisms in the soil near the landing sites. According to mission biologists, Mars is self-sterilizing. They believe the combination of solar ultraviolet radiation that saturates the surface, the extreme dryness of the soil and the oxidizing nature of the soil chemistry prevent the formation of living organisms in the Martian soil.

Other instruments found no sign of organic chemistry at either landing site, but they did provide a precise and definitive analysis of the composition of the Martian atmosphere and found previously undetected trace elements.

Data from the two Viking orbiters indicate that Mars was once been warmer and significantly wetter than it is today. Physical features closely resembling shorelines, gorges, riverbeds and islands suggest that great rivers and seas once covered the planet. Because life as we know it depends on water, scientists hold out the hope of finding fossiled evidence of life in the soil. Some scientists believe that life could still exist at the polar caps or in subsurface reservoirs.

In August 1996, a team of NASA research scientists announced they had found strong evidence of the remains of primitive life in a meteorite believed to have come from Mars. The scientists said the evidence points to the existence of a single-cell, bacteria-like organisms during early Martian history. The meteorite, discovered in Antarctica, is believed to have been blasted away from Mars by an asteroid or comet collision about 3.6 billion years ago. It crashed on Earth 1,300 years ago and was found by scientists in 1984.

Although the evidence is not conclusive, this discovery is potentially historic. For eons, humans have wondered if they are alone in the cosmos. If life developed on Mars, then this increases the likelihood that it has evolved on other planets throughout the Universe.

Atmosphere

The atmosphere of Mars is quite different from that of Earth. It is composed primarily of carbon dioxide with small amounts of other gases. The six most common components of the atmosphere are:

• Carbon Dioxide (CO2): 95.32%
• Nitrogen (N2): 2.7%
• Argon (Ar): 1.6%
• Oxygen (O2): 0.13%
• Water (H2O): 0.03%
• Neon (Ne): 0.00025 %

Martian air contains only about 1/1,000 as much water as our air, but even this small amount can condense out, forming clouds that ride high in the atmosphere or swirl around the slopes of towering volcanoes. Local patches of early morning fog can form in valleys. At the Viking Lander 2 site, a thin layer of water frost covered the ground each winter.

Temperature and Pressure

The average recorded temperature on Mars is -63° C with a maximum temperature of 20° C and a minimum of -140° C.

Barometric pressure varies at each landing site on a semiannual basis. Carbon dioxide, the major constituent of the atmosphere, freezes out to form an immense polar cap, alternately at each pole. The carbon dioxide forms a great cover of snow and then evaporates again with the coming of spring in each hemisphere. When the southern cap was largest, the mean daily pressure observed by Viking Lander 1 was as low as 6.8 millibars; at other times of the year it was as high as 9.0 millibars. The pressures at the Viking Lander 2 site were 7.3 and 10.8 millibars. In comparison, the average pressure of the Earth is 1000 millibars.

Mars Statistics

Characteristic	Measurement
Mass (kg)	6.421e+23
Mass (Earth = 1)	1.0745e-01
Equatorial radius (km)	3,397.2
Equatorial radius (Earth = 1)	5.3264e-01
Mean density (gm/cm^3)	3.94
Mean distance from the Sun (km)	227,940,000
Mean distance from the Sun (Earth = 1)	1.5237
Rotational period (hours)	24.6229
Orbital period (days)	686.98
Mean orbital velocity (km/sec)	24.13
Orbital eccentricity	0.0934
Tilt of axis	25.19°
Orbital inclination	1.850°
Equatorial surface gravity (m/sec^2)	3.72
Equatorial escape velocity (km/sec)	5.02
Visual geometric albedo	0.15
Magnitude (Vo)	-2.01
Minimum surface temperature	-140°C
Mean surface temperature	-63°C
Maximum surface temperature	20°C
Atmospheric pressure (bars)	0.007

Atmospheric Composition	Percent
Carbon Dioxide (C02)	95.32%
Nitrogen (N2)	2.7%
Argon (Ar)	1.6%
Oxygen (O2)	0.13%
Carbon Monoxide (CO)	0.07%
Water (H2O)	0.03%
Neon (Ne)	0.00025%
Krypton (Kr)	0.00003%
Xenon (Xe)	0.000008%
Ozone (O3)	0.000003%

Views of Mars

Sinusoidal Map of Mars

This image is a sinusoidal map of Mars. It was generated from a digitized airbrush map and was color-coded to represent elevation.

Schiparelli Hemisphere

This image is a mosaic of the Schiparelli hemisphere of Mars. The center of this image is near the impact crater Schiparelli, 450 kilometers in diameter. The dark streaks with bright margins emanating from craters in the Oxie Palus region, upper left of image, are caused by erosion and/or deposition by the wind. Bright white areas to the south, including the Hellas impact basin at extreme lower right, are covered by carbon dioxide frost.

Valles Marineris

This image is a mosaic of the Valles Marineris [VAL-less mar-uh-NAIR-iss] hemisphere of Mars. It is a view similar to that which one would see from a spacecraft. The center of the scene shows the entire Valles Marineris canyon system, more than 3,000 kilometers long and up to 8 kilometers deep, extending from Noctis Labyrinthus, the arcuate system of graben to the west, to the chaotic terrain to the east. Many huge ancient river channels begin from the chaotic terrain and north-central canyons and run north. Many of the channels flowed into a basin called Acidalia Planitia, which is the dark area in the extreme north of this picture. The three Tharsis volcanoes (dark red spots), each about 25 kilometers high, are visible to the west. Very ancient terrain covered by many impact craters lies to the south of Valles Marineris.

Central Candor Chasm - Oblique View

This image shows part of Candor Chasm in Valles Marineris. It is centered at Latitude -5.0, Longitude 70.0. The view is from the north looking into the chasm. Candor Chasm’s geomorphology is complex, shaped by tectonics, mass wasting, wind, and perhaps by water and volcanism.
Additional views from the south, east, and west can be obtained below.

• View from the south.
• View from the east.
• View from the west.

Landslide in Valles Marineris

Although Valles Marineris originated as a tectonic structure, it has been modified by other processes. This image shows a close-up view of a landslide on the south wall of Valles Marineris. This landslide partially removed the rim of the crater that is on the plateau adjacent to Valles Marineris. Note the texture of the landslide deposit where it flowed across the floor of Valles Marineris. Several distinct layers can be seen in the walls of the trough. These layers may be regions of distinct chemical composition or mechanical properties in the Martian crust.

HST 3 Views of Mars at Opposition

These Hubble Space Telescope views provide the most detailed complete global coverage of the Red Planet ever seen from Earth. The pictures were taken on February 25, 1995, when Mars was at a distance of 103 million kilometers. To the surprise of researchers, Mars is cloudier than seen in previous years. This means the planet is cooler and drier, because water vapor in the atmosphere freezes out to form ice-crystal clouds. The three images show the Tharsis, Valles Marineris and Syrtis Major regions.

Springtime on Mars: Hubble’s Best View of the Red Planet

This NASA Hubble Space Telescope view of Mars is the clearest picture ever taken from Earth, surpassed only by close-up shots sent back by visiting space probes. The picture was taken on February 25, 1995, when Mars was at a distance of approximately 103 million kilometers from Earth. Because it is spring in Mars’ northern hemisphere, much of the carbon dioxide frost around the permanent water-ice cap has sublimated, and the cap has receded to its core of solid water-ice several hundred kilometers across. The abundance of wispy white clouds indicates that the atmosphere is cooler than seen by visiting space probes in the 1970s. Morning clouds appear along the planet’s western (left) limb. These form overnight when Martian temperatures plunge and water in the atmosphere freezes out to form ice-crystal clouds. Towering 25 kilometers above the surrounding plains, volcano Ascraeus Mons pokes above the cloud deck near the western or limb. Valles Marineris is in the lower left.

Several other Hubble images are available:

• Tharsis Region, 160° Longitude.
• Syrtis Major Region, 270° Longitude.

Outflow Source of Channel Ravi Vallis

This image of the head of Ravi Vallis shows a 300-kilometer long portion of a channel. Like many other channels that empty into the northern plains of Mars, Ravi Vallis originates 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. The abrupt beginning of the channel, with no apparent tributaries, suggests that the water was released under great pressure from beneath a confining layer of frozen ground. As this water was released and flowed away, the overlying surface collapsed, producing the disruption and subsidence shown here. Three such regions of chaotic collapsed material are seen in this image, connected by a channel whose floor was scoured by the flowing water. The flow in this channel was from west to east (left to right). This channel ultimately links up with a system of channels that flowed northward into Chryse Basin.

Streamlined Islands

The water that carved the channels to the north and east of the Valles Marineris canyon system had tremendous erosive power. One consequence of this erosion was the formation of streamlined islands where the water encountered obstacles along its path. This image shows two streamlined islands that formed as the water was diverted by two 8-10 kilometer diameter craters lying near the mouth of Ares Vallis in Chryse Planitia. The water flowed from south to north (bottom to top of the image). The height of the scarp surrounding the upper island is about 400 meters, while the scarp surrounding the southern island is about 600 meters high.

Valley Network

Unlike the features shown in the above two images, many systems on Mars do not show evidence of catastrophic flooding. Instead, they show a resemblance to drainage systems on Earth, where water acts at slow rates over long periods of time. As on Earth, the channels shown here merge together to form larger channels. However, these valley networks are less developed than typical terrestrial drainage systems, with the Martian examples lacking small-scale streams feeding into the larger valleys. Because of the absence of small-scale streams in the Martian valley networks, it is thought that the valleys were carved primarily by ground water flow rather than by runoff of rain. 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.

South Polar Cap

This image shows the south polar cap of Mars as it appears near its minimum size of about 400 kilometers. It consists mainly of frozen carbon dioxide. This carbon dioxide cap never melts completely. The ice appears reddish due to dust that has been incorporated into the cap.

North Polar Cap

This image is an oblique view of the north polar cap of Mars. Unlike the south polar cap, the north polar cap probably consists of water-ice.

Dunefield

This image shows several dune types which are found in the north circumpolar dunefield. This thumbnail image shows a section of transverse dunes. The full image has a field of traverse dunes on the left and barchan dunes on the right with a transition zone in between. Transverse dunes are oriented perpendicular to the prevailing wind direction. They are long and linear, and frequently join their neighbor in a low-angle “Y” junction. Barchan dunes are crescent-shaped mounds with downwind-pointing horns. These dunes are comparable in size to the largest dunes found on the Earth.

Local Dust Storm

Local dust storms are relatively common on Mars. They tend to occur in areas of high topographic and/or high thermal gradients (usually near the polar caps), where surface winds would be strongest. This storm is several hundreds of kilometers in extent and is located near the edge of the south polar cap. Some local storms grow larger, others die out.

Lander 1 Site

Big Joe, the large rock just left of center is about 2 meters wide. The top of the rock is covered with red soil. The exposed portions of the rock are similar in color to basaltic rocks on Earth. This rock may be a fragment of a lava flow that was later ejected by an impact crater. The red color of the rocks and soil is due to oxidized iron in the eroded material. In some areas of this scene rocky plains tend to dominate, while a short distance away drifts of regolith have formed.

Lander 2 Site

Viking Lander 2 used its sampler arm to dig these two trenches in the regolith. The shroud that protected the soil collector head during the lander’s descent lies a short distance away. The lander’s footpad is visible in the lower right corner of the image. The rounded rock in the center foreground is about 20 centimeters wide, while the angular rock farther back and to the right is about 1.5 meters across. The gently sloping troughs between the artificial trenches and the angular rock, which cut from the middle left to the lower right corner, are natural surface features.

View From Lander 1

The Viking Lander 1 site in Chryse Planitia is a barren desert with rocks strewn between sand dunes. The lander’s footpad is visible at lower right; a trench in the foreground (just below center) was dug by the sampler arm. Patches of drift material and possibly bedrock are visible farther from the Lander.

View From Lander 2

The Viking Lander 2 site in Utopia Planitia has more and larger blocks of stone than does the Viking Lander 1 site in Chryse Planitia. The stones are probably ejecta from impact craters near the Lander 2 site. Many of the rocks are angular and are thought to be only slightly altered by the action of wind and other forms of erosion. Drifts of sand and dust are smaller and less noticeable at the Lander 2 site. The overall red coloring of the Martian terrain is due to the presence of oxidized iron in the regolith. The pink color of the sky is caused by extremely fine red dust that is suspended in Mars’ thin atmosphere.

Frost at the Viking 2 Lander

Viking Lander 2 is far enough north that frost deposits form on the surface during winter. This image, taken in May 1979, shows a thin, white layer of water frost, estimated to be only microns thick, covering parts of the surface. The reddish regions are soil and rock not covered by the frost. Portions of the spacecraft are visible in the right foreground.

Face on Mars

This image shows the Face on Mars that imaginative writers have cited as evidence for intelligent life on Mars. It is more likely that this hill, in the northern plains, has been eroded by the wind to give it a face like appearance.

Mars Moon Summary

The following table summarizes the radius, mass, distance from the planet center, discoverer and the date of discovery of each of the moons of Mars:

Moon	Number	Radius (km)	Mass (kg)	Distance (km)	Discoverer	Date
Phobos	I	13.5 x 10.8 x 9.4	1.08e+16	9,380	A. Hall	1877
Deimos	II	7.5 x 6.1 x 5.5	1.80e+15	23,460	A. Hall	1877