The lowlands are middle Amazonian to late Hesperian. The polar caps are the youngest, late Amazonian. The geology of Mars is divided into three main eras: the Noachian, the Hesperian and the Amazonian. This is a bit older than the current surface of the northern hemisphere which means that any telltale signs have been buried. The ocean would have existed 3.5 billion years or more ago. There has been speculation that the northern plains once were the site of a large ocean, at a time when Mars still had a reasonable atmosphere and climate. Utopia Planitia is the largest impact basin known in the solar system, more than 3000 kilometer across! It is far larger than the faint blue echo, and stretches towards the north pole: the true diameter is a quarter of Mars’ circumference. You have seen it: this is where Viking-2 took its images, and where more recently the Chinese rover (now apparently defunct) landed. This is Utopia Planitia, and is a sign of a massive impact crater, now deeply covered. On the right hand side there is a region of slightly deeper blue colours. In places, traces of the underlying topography remain visible. The reason is sedimentation or deposition: the real, much older surface is deeply covered. Why is the north so smooth? Clearly this is a much younger surface. This lowland covers about 1/3rd of Mars’ surface. North of it the land descends over a distance of about 1000 kilometers (30 degrees) until the edge of the green colours where it plummets into the lowlands. The edge of the redder colours – the highest highland – runs at an angle of about 20 degrees to the equator. The borderline between the two hemispheres is clearly visible in the map. The crust in the south is considerably thicker than that in the north. The dichotomy continues below the surface. The two poles look different from their henispheres, as from another world: these are the icecaps, consisting of frozen water that remains there permanently, and frozen CO2 that is permanent in the south but seasonal at the lower elevation of the north. The highland is rough and cratered while the north is smooth and -dare I say- boring. A very high resolution image can be found at or at google mars ( ) (It should have been three times more, due to the difference in gravity, but on Earth the oceans help carry some of the weight of the mountains and this allows them to grow higher than they should be able to.) Apart from a very deep hole in the south (the impact crater Hellas) the southern hemisphere is mostly highland and the northern hemisphere is mostly lowland, differing in elevation by 5 kilometers. The total range in elevation is 30 kilometers, 50% more than on Earth. The elevation map of Mars is shown below. Like the potato seedlings, there are small signs of life. But is its geology as dead as the surface implies? It turns out, almost. We have never seen a volcanic eruption on Mars. Ever since this has been a frozen planet – frozen in time. More than 3 billion years ago it lost most of its atmosphere. Once, this was a living planet with air and water and seas although probably without life (don’t tell NASA). It also has little erosion – what formed 4 billion years ago is still there. It has a ‘stagnant lid’, meaning that the surface does not move – it has no plate tectonics. In some ways, Mars has a different geology from ours. They are different from our volcanoes: larger, older, and immovable. (There are more things it is famous for, including some it doesn’t actually have, such as canals and three-legged blood-drinking aliens.) The supervolcanoes stand out from the planet – huge bumps on the red desert. But neither the book nor the film contains volcanoes. Literally so when the astronaut discovers they brought potatoes with them and starts farming. But the scenery is brilliant and it beautifully brings a dead planet to life. In the book, the habitat is instead on a boring plain, a far more likely place for a risky landing. The film includes the scene where he accidentally blows up the habitat (twice) but leaves out how he gets himself in a car crash – when being the only driver on the planet! The film was made in Oman and shows a mountainous desert landscape. What follows is a struggle for life, where science, engineering and agriculture(!) are used to keep the astronaut alive long enough to allow for a rescue attempt. It is about an astronaut who is accidentally (we hope) left behind on Mars during an emergency evacuation. The Martian is a fascinating book by Andy Weir.
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