content 20-March-2019 10:00:45

Background Science

The planet Mars, the fourth planet from the Sun and the seventh largest, boasts some of the most breathtaking scenery in the Solar System.

There are spectacular mountains three times as tall as Mount Everest, canyons three times as deep and five times as long as the Grand Canyon, vast ice fields and thousands of kilometres of features that are reminiscent of dry river beds on Earth.

Table of Martian Facts

Orbit:

227 940 000 km (1.52 AU) mean distance from Sun

Diameter: 6794 km

Martian day:

24 hours, 37 minutes and 22 seconds
Martian year: 669 Martian days 687 Earth days

Average temperature:

218 K (-55oC)

Minimum temperature:

140 K (-133oC) (at the winter pole)

Maximum temperature:

300 K (27oC) (summer dayside)

Surface area:

about the same as the land surface area of Earth

Highest mountain:

Olympus Mons - the largest mountain in the Solar System rising 24 km above the surrounding plain. Its base is more than 500 km in diameter and is rimmed by a cliff 6 km high

Largest canyon:

Valles Marineris - a system of canyons 4000 km long and from 2 km to 7 km deep, and up to 20 km wide.

Largest impact crater:

Hellas Planitia - an impact crater in the southern hemisphere over 6 km deep and 2000 km in diameter

Surface bulge:

Tharsis - a huge bulge on the Martian surface that is about 4000 km across and 10 km high

Mars is a smallish planet - its radius is just a little over half the Earth's. Yet it boasts scenery on a scale that makes Mount Everest and the Grand Canyon seem puny by comparison.

Topography map of Mars compiled by NASA's Mars Global Surveyor

It has the highest volcano in the Solar System, Olympus Mons, which stands at 26 km above the surrounding plain: Mount Everest is only a third the height. Olympus Mons lies at the western edge of another gargantuan feature, the Tharsis dome, which is a 10 km high, 4000 km wide bulge on the Martian surface. Dotted in the middle of Tharsis are the Ascraeus, Pavonis and Arsia volcanoes, all of them higher than Mount Everest. And running from the eastern flanks of the rise, roughly along the equator, is Valles Marineris, a split in the Martian crust 4000 km long (about a fifth of the Martian circumference), up to 600 km wide and 7k m deep. The Grand Canyon is a mere 800 km long, up to 29 km wide and 1.6 km deep.

Then there is the Hellas Basin in the southern hemisphere, which is a massive impact crater 2300 km in diameter and more than 9 km from top to bottom. The bottom of the Hellas Basin has the lowest elevation on the planet. But perhaps most striking of all is the general difference in height and surface roughness between the northern and southern hemispheres. A quick glance at the map above shows a southern hemisphere pock marked with craters and with generally much higher terrain than the relatively smooth northern hemisphere.

This map was compiled in summer 1999 from data recorded by the Mars Orbiter Laser Altimeter (MOLA) on board NASA's Mars Global Surveyor (MGS) spacecraft. MOLA is measuring the height of the Martian surface to within 13 metres of elevation on average; the heights of some parts of the Earth aren't known so accurately. It has revealed for the first time that the slope from south to north is gradual and that the average elevation in the south is 6 km higher than in the north.

Image of Mars taken from NASA's Viking spacecraft showing the Valles Marineris canyon in the middle of the image and the Tharsis volcanoes on the western edge of the planet

What caused this North-South divide? What were the forces that created the other features in Mars' spectacular landscape? And when did they cease? Or do some of them still exist today? Volcanism and tectonics have clearly been important - but what was, or is, their role? Answering these questions involves developing models of the interior and hypotheses about the planet's formation and evolution. The nature of the interior, in turn, has implications for the existence of a magnetic field. Mars has a very weak field today, but there is evidence that it had been a much stronger field early in its history. What happened that turned it off?

Such questions may seem highly specialised, of interest only to planetary geologists. But the answers will shed light on the really big questions about Mars, such as the fate of the water that almost certainly existed on the planet in its early history; whether Martian life exists, has ever existed, or could have existed at some time in the past; and even whether Mars could make a hospitable venue for human exploration.

MOLA is not the only instrument on MGS to be returning exciting new data. The camera is taking sharper shots of surface features than ever before, revealing for the first time layers in the rock and soil over much of Mars. Also caught on camera are dust storms and dust devils which give clues about the Martian weather and processes in the atmosphere.

MGS and Mars Odyssey are returning significant data about Mars and were recently joined by the Mars Express orbiter that arrived 25 December 2003. They will be joined by more spacecraft in the future as an unprecedented number of space vehicles are due for launch to Mars before 2010 under the auspices of an international effort to explore the red planet. Each will expand and add new dimensions to our knowledge.

 


Last Update: 07 August 2006

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