Visions of the Cosmos

Planetary Science

The Solar System

Planet Mars

Mars -The Cold Red Wilderness


The Twin Peaks are modest-size hills to the southwest of the Mars Pathfinder landing site. Caption Courtesy NASA

 One day in the second or third decade of the twenty-first century men and women, dressed in large, white padded space suits, will stand upon the Martian wasteland and gaze towards the sky.    Sometimes dust storms will hide the disc of the Sun by day and the splendour of the stars by night and they will see nothing.   At other times, when the dust has settled, the sky will clear and constellations of stars will bejewel the darkness of the night and shine down upon the cold and arid wilderness.   Shortly before dawn the 'morning star' will appear as a resplendent blue gemstone on the eastern horizon.   No doubt, they will feel pangs of homesickness as they watch the Earth appearing like a brilliant amethyst, in the Martian sky a little before sunrise.   As day breaks on the horizon they will behold the small disc of the Sun, which from that distance will only look two thirds as large as it does from Earth and only half as bright.   The Sun will rise into a pink red or brownish sky. Before the dawn of the space age, it was envisaged that the skies of Mars would look a deep blue.  However, on Mars the sky is usually pink. During the frequent sand storms, tiny particles of dust one thousandth of a millimetre in diameter ascend up to altitudes of 45 kilometres and take months to clear. These tiny dust particles scatter red light more effectively than light of any other wavelength and account for the colour of the sky.

The astronauts who make the first historic voyage to the red planet have probably already been born and are sleeping in their cots and prams blissfully unaware of their amazing future.  Some of the knowledge they will need for their journey has already been learnt and during the next twenty years more orbiting spacecraft and landers will prepare a base camp for the first intrepid explorers from Earth.

The earthlings must keep warm in their space suits and well protected from solar radiation.  Since there is no ozone-layer, the ultraviolet is intense enough to rapidly cause severe sunburn on unprotected skin.   Also, without a magnetosphere to act as a barrier against the ferocity of the solar wind and cosmic radiation, our explorers will need shielding from the stream of high-energy particles that incessantly rain down upon the surface of this tormented world.

Mars is now a permanently cold sandy desert where the atmosphere is very thin and the pressure too low for water to exist as a liquid.   The first humans to land on Mars will already be well supplied with maps and details of the terrain.  The planet has already been extensively mapped and by the time a human expedition visits the red planet even more will have been learnt about the conditions that they are likely to encounter.

Perhaps one of the astronauts on gazing at the blue Earth just before the martian dawn will be of a literary mind and recall the poem written by Alfred Lord Tennyson in 1886


Hesper-Venus-were we native

                to that splendour or on Mars,

We should see the Globe we groan in,

                fairest of their evening stars.


Could we dream of wars and carnage

                craft and madness, lust and spite,

Roaring London, raving Paris

                in that point of peaceful light?


Well as far as Mars is concerned the poem was certainly prophetic -.  Not of course for Venus but Tennyson and plenty of romantics, among them many scientists, thought that Venus might be a tropical paradise.  It took the coming of the space agent to tell us what Venus was really like - the nearest thing to hell in the Solar System and with no clear night skies to gaze upon the Earth in space

It is heartening to know that the American Mars Pathfinder which landed On 4 July 1997  in the Ares Valli which was  named the Carl Sagan Memorial Station in memory of the famous astronomer who so sadly died just before the landing took place and that the small vehicle that travelled over the surface and was named Sojourner after a black woman from the deep-south who lived during the nineteenth century.  She was the daughter of slaves and was for a while a slave herself.  She was one of the first 'civil rights' campaigners even that long ago. Source: Abraham Lincoln: The War Years Vol. 2, Harcourt, Brace & World, Inc photograph circa 1862) Hyperlink to article on Sojourner Truth given at end of this section of the web-page.  Credit for illustration of space vehicle NASA/JPL.

The Topology of Mars

            The Instruments of the Mars Global Surveyor [Mars Global Surveyor Instruments]                  

Acknowledgement for diagramto MOLA Science Team NASA/JPL

Mars has been Extensively mapped.  The maps usually referred to are taken from the Mars Global Surveyor which is a US spacecraft developed by NASA and the Jet Propulsion Laboratory (JPL) and launched in November 1996.  It carried a number of instruments on board including the Mars Orbiter Laser Altimeter usually referred to as MOLA The instrument transmits infrared laser pulses towards Mars at a rate of 10 Hz and measures the time of flight to determine the range of the MGS spacecraft to the Martian surface. Range measurements have used to construct a precise topographic map of Mars that has many applications to studies in geophysics, geology and atmospheric circulation.

The MOLA Map of Mars

Global topographic map of Mars with major surface features labelled. (Credit: MOLA Science Team).  The colours indicate ALTITUDE.  The blue represents fairly low lying ground NOT a sea.  The white represents the very high ground ot the top of the highest mountains  NOT a snow region.

Globes of Mars

Just as globes of the earth are on sale it is possible to obtain globes of Mars.  There are at least two varieties available.  There is one type that is illustrated in various shades of brown to give the altitudes and whilst being instructive enough is rather drab compared to the other one which illustrates altitudes in the same colours as the maps shown above.

Both types of globe are obtainable at the European Astrofest which is held every February at the Kensington Town Hall in London.  At the time of writing this web-page (mid January 2007) the next Astrofest is only a short time away  9-10 February 2007.

Main Features

On the top left hand side of the map the great region known as the Tharsis bulge is clearly labelled

MOLA Regional Map of the Tharsis and Chryse Regions

Topography in the Tharsis rise (left) and Chryse region (right). . The color scale is the same as that used on the main map of the whole of Mars. 

The Tharsis region on Mars is an enormous volcanic upland located on Mars' equator, at the western end of Valles Marinerus. Its name comes from the bible, where it was the name for the land at western extremity of the known world.  Thought to be a region in modern-day Spain    In this high-elevation part, there is an impressive uplifted continent about the size of North America called the Tharsis bulge. Rising about 10 km above the average height, this bulge contains a great 5000 mile rift called Valles Marineris and four great volcanoes. The largest of these volcanoes is Olympus Mons which rises another 15 km above the continent. It is thought to have been formed by a mantle plume over a period of about a hundred million years during the Noachian Period (between 3.8 and 3.5 billion years ago).

Obvious on the map are the major Tharsis volcanoes: Olympus Mons (18° N, 228° E), Alba Patera (40° N, 250° E) and the volcanic chain consisting of Ascraeus, Pavonis and Arsia montes. Note that Olympus Mons sits off to the west of the Tharsis rise and Alba Patera is separated from the main dome that contains the Tharsis montes. Note again that at the high elevations of the volcanoes the color scale shows white -- those are NOT snow-capped peaks!

The new grid also shows improved detail in Valles Marineris and verifies our earlier observation that the eastern part of the canyon is about a kilometer in elevation below the mouth of the Chryse outflow channels.

The map also clarifies aspects of early water transport on Mars. In the Chryse region (330° E) there is detailed structure where outflow channels debouch into the northern plains that indicates that water flowed well beyond the channel mouths into what previously appeared to be relatively featureless plains.

This figure appeared in the October 1999 issue of Physics Today. (Credit: MOLA Science Team)

The table below compares the very approximate altitude differences in the three planets Venus, Earth and Mars. They are given purely for interest to show how much greater Mars is in the differences in altitude compared to the other two planets.  It should be noted that the Martian mountains are thought to be due to hot spots deep within the mantle.  Although there are very large volcanic mountains on the Earth such as Mauna Kea in Hawaii, the highest mountains, the Himalayas,  were formed by tectonic plate collisions.     If plate tectonics ever existed on Mars it was very early in its history.  The absence of plate tectonics would have allowed extremely large shield volcanoes to form.  It should also be noted that Venus and especially the Earth have much higher surface gravities than Mars.  Volcano growth will also be aided by the low gravity on Mars.

Planet Highest mountain Deepest Chasm Altitude Difference
Venus Maxwell Mons     10,800 meters Diana Chasma        2000 meters 13 kilometers
Earth Everest                  8,000 meters Marianus Trench   10,000 meters 18 kilometers
Mars Olympus Mons    27,000 meters Hellas Crater          6,000 meters 33 kilometers

Valles Marineris

Valles Marineris is the great rift which is almost as long as the USA coast to coast.  It has been magnificently photographed by the European Space Agency's  Mars Express Cameras

Date: 19 Jan 2004
Satellite: Mars Express
Depicts: Valles Marineris
Copyright: ESA/DLR/FU Berlin (G. Neukum)

Picture taken with the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express orbiter on 14 January 2004 under the responsibility of the Principal Investigator Prof. Gerhard Neukum.

It was processed by the Institute for Planetary Research of the German Aerospace Centre (DLR), also involved in the development of the camera, and by the Institute of Geosciences of the Freie Universität Berlin.

It shows a portion of a 1700 km long and 65 km wide swath which was taken in south-north direction across the vast canyon system on Mars - Valles Marineris.

Courtesy  photo and script European Space Agency.

Impressive images of a major trough in the Valles Marineris system called the Coprates Chasma were taken on 10 June 2005 by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft.  Coprates Catena lies parallel to Coprates Chasma and can be seen in the south (left) of the image as three troughs, ranging from a few kilometres to 22 km wide and up to 5 km deep

Photograph Coprates Chasma and Catena - looking north Courtesy ESA Mars Express

Impressive images of a major trough in the Valles Marineris system called the Coprates Chasma were taken on 10 June 2005 by the High Resolution Stereo Camera (HRSC) on board ESA’s Mars Express spacecraft.  Coprates Catena lies parallel to Coprates Chasma and can be seen in the south (left) of the image as three troughs, ranging from a few kilometres to 22 km wide and up to 5 km deep.

The scenes show the region containing sections of Coprates Chasma and Coprates Catena, over an area centred at about 13.5º South and 300º East, roughly in the centre of the Valles Marineris canyon system are improving our understanding of this fascinating planet.

Valles Marineris provides scientists with a window into the depths of Mars and enables them to study the complex geological and climatic history of the Red Planet.

Scientists are unsure of the mechanism responsible for the creation of the Valles Marineris canyon system. Some suggest that the formation of the Tharsis uplift, located west of the canyon system, caused tension and fracturing of the Martian crust.

Other researchers believe that water may have removed rock material from the subsurface, which caused the surface to collapse. A related theory suggests that large quantities of subsurface ice melted, causing surface collapse. Possibly all of these processes together were active in forming the structure.

Olympus Mons


This picture composed by The MOLA team clearly shows how large and flat Olympus Mons is. Although the volcano is nearly 27 km high, it is over 20 times wider than it is tall. Thus, most of the volcano has a fairly gentle surface slope. The image also shows the distinct cliff which marks the base of Olympus Mons. In places, this scarp is up to 6 km high. In other places, it is hidden under lava flows cascading out into the surrounding lava plains.Photo Courtesy NASA MOLA team


View from overhead of the complex caldera (summit crater) at the summit of Olympus Mons on Mars, the highest volcano in our Solar System. European Space Agency Mars Express released 11 February 2004

View from overhead of the complex caldera (summit crater) at the summit of Olympus Mons on Mars, the highest volcano in our Solar System. European Space Agency Mars Express released 11 February 2004
Olympus Mons has an average elevation of 22 km and the caldera has a depth of about 3 km. This is the first high-resolution colour image of the complete caldera of Olympus Mons.

The image was taken from a height of 273 km during orbit 37 by the High Resolution Stereo Camera (HRSC) on ESA’s Mars Express on 21 January 2004. The view is centred at 18.3°N and 227°E. The image is about 102 km across with a resolution of 12 m per pixel. South is at the top.  

The perspective view in the right picture shows the southern part of the caldera (summit crater) of the Olympus Mons volcano on Mars.

The Hellas Basin

Almost antipodal to the Thasis Region with its huge volcanoes and its system of canyons of the Valles Marineris is another very distinctive feature on Mars.  It is the Hellas Basin.

A close-up view of Martian topography from MOLA showing the Hellas Basin. Blue tones represent elevations of less than 2 kilometers, while reddish tones are greater than about 2.8 kilometers, relative to the mean equatorial height of Mars. Courtesy MOLA Science Team
The Hellas Basin is enormous - it is nearly nine kilometers deep and2,100 kilometers across.  It is surrounded by a ring of material that rises about two kilometers above the surroundings and stretches out to 4,000 kilometers the center of the basin.  This is consistent with the hypothesis that the basin was created by an impact with an asteroid.  It is noteworthy that the Hellas Basin is approximately antipodal to the Tharsis Bulge.

The Polar Ice Caps

The physical chemistry of H2O molecules and CO2 molecules are the main factors in controlling the weather on Mars.  Firstly, the behaviour at the ice caps is governed by the properties of these two substances.  It is important to realise that by ICE we mean water  (H2O) ice AND carbon dioxide (CO2) ice.   CO2 ice is often called dry ice.  This in turn affects the changes in pressure over the whole planet that causes the winds and the violent planet wide dust storms.

Both the North Polar Regions and the South Polar Regions have permanent ice caps throughout the whole year.  In both cases there is a residual ice cap which is permanent and persists throughout the year and a seasonal ice cap which waxes and wanes with the seasons and reaches its greatest extent during the winter.

Like Earth, Mars is inclined on its axis.  The inclination of the axes of the two planets is similar; Earth 23.4° and Mars 25°.  As a consequence of this Mars shows seasonal variations like Earth.   By another coincidence the period of rotation of Mars is only slightly longer than ours.  The Martian day of just over 24 hours and 37 minutes has been given the name of a SOL.  The Martian year is considerably longer than that of the Earth, being 687 Earth days.   As far as the climate is concerned there is another important factor imposed of the climate of Mars and that is the fact that it has a far more elliptical orbit than the Earth.  As a result of this there is a much greater percentage difference in its distance from the Sun at perihelion (the nearest) and aphelion (the furthest) when compared to the Earth.   Mars experiences considerable differences in the amount of radiation it gets from the Sun throughout its year - it gets about 40% more at perihelion than at aphelion. This affects the climatic differences between the two hemispheres much more than it does on Earth.  The table illustrates the difference in the distances from the Sun of Mars, Earth, Venus and Mercury together with the lengths of the 'year' and the 'day' for each planet

Approximate Distances of Mercury, Venus, Earth and Mars from the Sun

Planet Perihelion nearest to Sun Aphelion furthest from Sun 'Year' in Earth days 'Day' in Earth days
Mercury 45,900,000 kilometres 69,700,000 kilometres 87.97 days 58.65 days
Venus 107,400,000 kilometers 109,000,000 224.7 days 243.0 days
Earth 147,000,000 kilometers 152,000,000 365.26 days  24 hours (1 day)
Mars 206,000,000 kilometers 249,000,000 687 days 24hrs37mins22.6secs

The southern summers are shorter but hotter than the northern summers since at this time Mars is closest to the Sun.  On the other hand, the southern winters are far colder than the northern winters when Mars is furthest from the Sun.   The percentage difference for the Earth is quite small and anyway many other factors play important roles in seasonal differences on Earth.   However there is a big percentage difference in the planet-sun distances for Mars and the effect is very marked.

The Southern Hemisphere, particularly in the polar-regions, is extremely cold in winter.  During the winter time temperatures as low as -113°Celsius have been recorded and at these low temperatures very little if any water vapour was detected. Almost all the H2O will be in the form of water ice.  On the other hand considerable amounts of carbon dioxide sublime out to form the seasonal polar ice cap.   Despite the fact that the south polar-regions in general have warmer summers than the north but it is thought that there is so much solid CO2 formed in the winter that it does not all vaporise in summer. Therefore, the southern residual ice is almost certainly a mixture of both water-ice and solid carbon dioxide.   The south polar cap shows a much greater variation than does the north.   In mid-winter it extends as far as 50° South: for comparison the north only extends about 65° during the northern mid-winter.

OMEGA Visible and Infrared Mineralogical Mapping Spectrometer 
OMEGA builds up a map of surface composition.It will determine mineral composition from the visible and infrared light.   reflected from the planet's surface. As light reflected from the surface must pass through the atmosphere before entering the instrument, OMEGA will also measure aspects of atmospheric composition. "We want to know the iron content of the surface, the water content of the rocks  and clay minerals and the abundance of non-silicate materials such as carbonates and nitrates," says Jean-Pierre Bibring, OMEGA PI from the Institut d’Astrophysique Spatiale, Orsay, France.

Thanks to ESA’s Mars Express, we now know that Mars has vast fields of perennial water ice, stretching out from the south pole of the Red Planet.
Astronomers have known for years that Mars possessed polar ice caps, but early attempts at chemical analysis suggested only that the northern cap could be composed of water ice, and the southern cap was thought to be carbon dioxide ice.

Recent space missions then suggested that the southern ice cap, existing all year round, could be a mixture of water and carbon dioxide.

Only with Mars Express have scientists been able to confirm directly for the first time that water ice is present at the south pole too. The results showed that hundreds of square kilometres of ‘permafrost’ surround the south pole. Permafrost is water ice, mixed into the soil of Mars, and frozen to the hardness of solid rock by the low Martian temperatures. This is the reason why water ice has been hidden from detection until now - because the soil with which it is mixed cannot reflect light easily and so it appears dark. OMEGA observations were made between 18 January and 11 February 2004 this year, when it was late summer for the Martian southern hemisphere and temperatures would be at their highest. Even so, that is probably only –130 degrees Celsius and the ice that Mars Express has observed is a permanent feature of this location.

OMEGA looked at the surface of the polar ice-cap with infrared eyes and, being sensitive to heat, clearly picked up the signature of water ice. The discovery hints that perhaps there are much larger quantities of water ice all over Mars than previously thought. sing this data, planetary scientists now know that the south polar region of Mars can be split into three separate parts. Part one is the bright polar cap itself, a mixture of 85% highly reflective carbon dioxide ice and 15% water ice.

The second part comprises steep slopes known as ‘scarps’, made almost entirely of water ice, that fall away from the polar cap to the surrounding plains.

The third part was unexpected and encompasses the vast permafrost fields that stretch for tens of kilometres away from the scarps

Mars Express and OMEGA will now continue looking for water ice and minerals across the surface of the planet. In May, another Mars Express instrument, the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) is alsocollecting data, looking for water underground.

Picture on right shows ice and dust in north polar regions Picture Courtesy ESA

Another Mars Express instrument, the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) has quickly detected what appeared to be water ice extending as deep as 3.5 kilometres below the southern polar and stretching 1.8 kilometres below the surface of the northern polar ice cap. Now, it has found what looks like water ice it will begin collecting data, looking for water underground.  MARSIS is looking at the south pole in particular because, once planetary scientists know how deep the ice reaches, they will be able to calculate exactly how much water there is. Knowing this is very important to understand how Mars evolved and if it ever harboured life.   Water may once have flowed freely on Mars and, like the Earth, the planet receives sunlight and has its own internal energy source. So the odds on primitive life thriving for at least some time during the planet’s history are reasonably good.

Global dust storms coincide with the retreat of the southern polar cap near perihelion.  A large temperature gradient exists at perihelion between the newly exposed south circumpolar surface and the residual southern ice cap.  These factors are thought to be sufficient to generate winds fierce enough to inject large amounts of dust into the atmosphere.  Dust in its turn has a positive feed back effect since the presence of dust causes a temperature rise in the atmosphere that tends to raise more dust.  This can lead to the large global dust storms that occur in the planet's atmosphere from time to time.

In the North Polar Regions, during the northern winter, both water molecules and carbon dioxide molecules sublime out to form the seasonal polar ice cap.  However in the summer all the carbon dioxide is believed to enter the gas phase.  Therefore, the northern residual ice cap is almost certainly water ice only.  

Sand dunes and ongoing movements of sand across the planet have been observed in the North Polar Regions.   The North Polar Cap is surrounded by a zone of dark dunes, which contain fragments of rock and minerals 0.06-2.0 millimetres in diameter.  The sand appears to have been transported by wind in one of two ways - by hopping over the ground, which is called SALTATION or by rolling along the ground, a process known as TRACTION.  Some of the dunes are covered with thin bright frost, which is intersected by dark streaks.

.The Atmosphere of Mars

The present atmosphere consists mainly of carbon dioxide with traces of nitrogen, noble gases and water vapour.

There is clear evidence that, although Mars is now a cold desert with a very low atmospheric pressure, it passed through at least one warm phase in which there were large amounts of running water on the surface. This is backed up by the results of the Viking and Pathfinder landings, by successful orbiters, and by the observations of Earth-based telescopes and the Hubble Space Telescope.

The Climate of Mars

On Mars the ambient temperature can range between minus 125º Celsius and plus  27º Celsius although for almost all of the time it lies well below zero Celsius all over the planet.   However on a very warm Martian day near the equator the temperature can rise as high as 27º Celsius above zero during the early afternoon.  Even then the temperature drops very sharply at night.   Under the low conditions of temperature and humidity H2O always sublimes directly to ice (frost) when it reaches the saturation partial pressure.  This process of sublimation is very important on Mars where the ambient pressure is very low and H2O does not appear to exist in the liquid state anywhere on the surface.   The 'morning mists ' which are sometimes observed at dawn are due to ice crystals subliming out directly from the vapour phase.  Later in the morning the mist clears as the temperature rises and the ice changes back directly to the gas phase.

The Pathfinder Mission took place during the summer 'months' of the Northern Hemisphere of Mars.

Extensive monitoring of the weather was carried out during the Mission.  Pressure variations during the day could change considerably by as much as 0.3 millibars (4.5% of the average pressure on Mars).

Frozen water-ice clouds appeared in the morning over the Pathfinder site and evaporated as the temperature rose.

Cloud Formation on Mars

Both water and carbon dioxide form clouds.    Clouds often appear above the equatorial regions around mid-day.  At these times the warming of the air is at its greatest causing the warm air to rise so that ice crystals condense (sublime) out to form clouds.  Clouds quite often appear around the Tharsis Volcanoes, which are at a very high altitude.

Fogs, which appear to consist of both solid H2O and CO2, appear at sunrise particularly in the depths of the canyons.

Dust Storms on Mars.

From time to time in the thin air of the red planet vast dust storms blow across the cold dry sands obscuring its surface from outside observation.  Sometimes wind speeds up to 400 kilometres an hour are reached. Dust storms are a feature of the Martian seasonal cycle.  During 1977, the Viking Mission recorded a total of 35 storms.

In May 1999 the Hubble Space Telescope picked up evidence of a colossal storm.   The hurricane probably formed as frozen CO2 at the North Pole sublimed rapidly to the vapour phase during the northern summer leaving water ice behind.  The temperature difference between the bright ice-cap and the warm dark sand caused a very high wind to arise.  The eye of the hurricane was about 320 kilometres in diameter and the whole system was 1,700 kilometres across (see New Scientist report 29 May 1999).

The Terraforming of Mars

This may well be a subject of great controversy of the future.  There will be some who will want to planetary engineering want to transform Mars into a second Earth by a huge effort of planetary engineering.  There will doubtless be many more against it.

Even though it is much smaller in mass and diameter the land area of Mars is almost as large as Earth because Earth's surface is covered by about three quarters water.  Even so a terraformed Mars will at the very least require large stretches of water.

The total surface area of the Earth is 510.1 million square kilometres, most of which is ocean.  The Total Land Surface Area of the Earth 149.8 million square kilometres.   Although Mars is a far smaller planet than the Earth, the land surface area of Mars is coincidentally almost the same.  The surface area is of Mars is 145.0 million square kilometres.                                                         

Any human beings and any other animals born and raised on Mars will be subjected to a lower gravity and would be unlikely ever to go to be able to tolerate the higher gravity of Earth.

One very important point about space vessels going to Mars for a return trip to bring back rock samples is the question of life.

Apart from the already acknowledged danger of contaminating Mars with earthly organisms there is the far more serious possibility of bringing back from Mars any primitive Martian organisms and contaminating Earth 

 An excellent book by Arthur C Clarke entitled  ‘The Snows of Olympus’ deals with the terraforming of Mars was published  

Mars Space Missions

The subject of Mars Space Missions is dealt with in another page of the web-site


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