Get to know Mars - 1

OLYMPUS MONS.  The line of zero longitude on Mars is taken as passing through a sharp pointed area of dark surface.  It is named Sinus Meridian and it forms part of the dark area Sinus Sabaeus.

From this line of longitude, situated 178° West and 17° North of the Equator, lies Olympus Mons.  Previously it was called Nix Olympia, the Snows of Olympus, a name given to it by Giovanni Schiaparelli, because from time to time a bright spot occurred there.  Mariner 9 and the Viking probes in 1972 and 1976 showed Nix Olympia to be a vast volcano.  Now Mars Global Surveyor which has been orbiting Mars since 1997 has accurately measured by means of its radar altimeter that the height of the top of the mountain above the modal plane (the most average elevation of the surface of Mars) to be 21 km 287,4 metres and that its base extends over 600 km with cliffs 1 km high around the periphery.  It is thus 2,4 times the height of Mt. Everest and its base would cover the whole Orange Free State and most of Natal.  It is so big that if an astronaut were to land on its sloping side, he would not be able to see the mountain. All that he would be able to see is a very gently sloping lava-covered surface having a slope of 1 in 12.  Beyond 40 to 50 kilometres from his vantage point, the surface vanishes below the horizon.  Similarly, if the astronaut stood at the edge of the caldera, 65 km wide, he would not be able to see the rim on the other side -- it would be below the horizon.  The only way to see Olympus Mons is to orbit the planet in a space vehicle.  By comparison the Earth's largest volcanoes, Mauna Loa and Mauna Kea in the Pacific Ocean, pale into insignificance.

The bright spot has turned out to be clouds of fine crystals of carbon dioxide which, from time to time, condense out of the atmosphere.  The sparse scattering of craters in the solidified lava of the slopes, indicate that the last flows of lava from the caldera could not have taken place more than 10 to 100 million years ago and that it is geologically very young, not more than one-fifteenth of Mars' lifetime.  During thousands of millions of years the volcano erupted a great amount of lava which was driven upwards by steam.  Because the gravity of Mars is only 0,38 that of the Earth, the escape velocity from Mars is only 5,2 km/sec compared to the Earth's 11,2 km/sec.  That is why the Martian volcanoes have such enormous sizes.  Because of the very low temperature on Mars, the steam gushed out, would immediately have crystallised into fine globules of ice.  It is unimaginable with what force the torrential falls of ice particles which flowed like water, sweeping great watercourses in the sandy soil.  These watercourses are still visible today.

To the east of Olympus Mons, but still on the Tharsis Highlands there another three vast volcanoes in a straight line north-east to south-west: Ascreaus Mons 18,2 km high, Pavonis Mons 14,1 km and Arsia Mons 17,8 km high.  All this water from the steam gushed by these volcanoes, swept over Tharsis and on the east swept into Valles Marineris, the greatest canyon anywhere in the Solar System.  The waters collected  over the low-lying areas to the North: Chryse Planitia, Acidalia Planitia, Utopia Planitia and Vastitas Boreal is and formed a great ocean.  It is not known how long this ocean lasted.  It has however long since soaked into the soil where it today is being discovered as permafrost and has also evaporated into space so that Mars is today considered to be utterly dry.  At full blast the steam and lava which gushed out of Olympus Mons' 65 km wide caldera must have been a sight visible from the Earth 10 or more millions of years ago.

Jan Eben van Zyl