By Sabine Stanley Ph.D., John Hopkins University
When missions to Mars send back images, Mars’s mountains make up much of their view. However, the mountains have more than a decorative role, especially as many are volcanoes. Mars has a volcanic province, with many craters, quakes, and features that are similar to the Earth. So, what are the differences other than the atmosphere and gravity?
Many of Mars’s mountains and volcanoes are concentrated in Tharsis, the volcanic province that is around 3,000 miles across. The province is near the equator and has four significant volcanic domes. Three of the volcanoes form a line: Ascraeus Mons, Pavonis Mons, and Arsia Mons, with the tallest of these three being Ascraeus Mons at around 11 miles high. However, the tallest one in Tharsis is Olympus Mons.
Olympus Mons
Northwest of the three tall volcanoes is the 16-mile-high Olympus Mons, almost three times higher than Mount Everest. It is the largest known mountain in the solar system, with a diameter of about 375 miles, and a 50-mile-wide caldera at the summit. The caldera is over two miles deep, and its last active lava eruption happened 115 million years ago.
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Valles Marineris and Craters
Other than impressive mountains, Mars also has remarkable canyons. Valles Marineris is a system of canyons, over 2,500 miles long, up to 120 miles wide, and sometimes over four miles deep. The canyon was formed as a tectonic crack when Mars was cooling, and the Tharsis region was forming next door. Later, there might have been a river of water or lava flowing through it as well.
Apart from the canyons, there are numerous impact craters. The two most significant ones are Hellas and Argyre, formed around 3.9 billion years ago. Unlike Earth, whose impact craters are now buried deep due to plate tectonics, Mars has kept them all where they happened. All these make Mars a difficult place to land on.
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Surface of Mars
Finding a place that is scientifically interesting but also safe to land on is a challenge on Mars. The landing site must be fairly flat, with not many rocks to knock over the lander.
One of the first places explored was called Chryse Planitia—Plains of Gold—an impact crater, northeast of Tharsis and Valles Marineris. Long ago, water flowed in the region. Viking One in 1976 sent the first images of Mars’s rocks, dust, and dunes of sand. Ares Vallis, a huge outflow channel leading into Chryse Planitia, was visited by the Mars Pathfinder lander and the Sojourner rover.
The geological analysis of places like the rock Barnacle Bill showed that their composition is pretty similar to volcanic rocks on Earth, called andesite. The other rock studied was Yogi, the first basaltic rock found on Mars. The rounded pebbles at the landing site showed there used to be running water in the past. The other discovery was that the dust is magnetic.
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Utopia Planitia, Half a World Away
Utopia Planitia is another huge impact crater with a diameter of over 2,000 miles. Around the time when Viking One was exploring Chryse Planitia, Viking Two was in Utopia Planitia. The rocky surface is covered in frost every morning, and the topography is bizarre. There are scallops that were perhaps formed when subsurface water ice sublimated due to a sudden impact of the low surface pressure.
In 2016, the Mars Reconnaissance Orbiter showed more evidence that there is water in the subsurface of Utopia Planitia. Before that, in 2004, the Mars Exploration Rover Spirit picked Gustav crater as a landing place. Spirit also found mineral hematite in some rocks that could only have been formed if water was there.
More Evidence of Past Water on Mars
On the other side of Mars, Opportunity landed to explore Meridiani Planum while Spirit explored the Gusev crater. Opportunity visited over ten smaller craters to find the same thing that its twin had: evidence of past water in the gray hematite.
Gale crater, a 3.5–3.8 billion-year-old phenomenon, was the next rover stop. It has a diameter of around 93 miles and also indicated evidence that there used to be water. It is, perhaps, a dried-up lakebed, judging by its water-rich sands, organic chemicals, and layers of sediments.
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Mars’s Features as a Planet
Mars has a crust, mantle, and an iron-rich core. The composition is very similar to Earth, with an average density of about 4,000 kilograms per cubic meter. There used to be a magnetic field since some rocks in the oldest regions are magnetized. Mars’s dynamo must have died four billion years ago, based on crater counting of magnetized surfaces.
In 2018, the Mars InSight mission placed a seismometer on Mars to record ‘marsquakes’. Even though there were many vibrations, the marsquakes were so different, as well as when they were transferred to the audible range.
Overall, Mars has a mainly uneven surface with lots of vibrations, either from quakes or from storms, and has a lot of evidence of a water-rich past.
Common Questions about Mars’s Mountains
Olympus Mons is the tallest mountain on Mars. It is 16 miles in height, i.e., three times higher than Mount Everest on Earth.
Mountains were formed on Mars in almost the same way as Earth’s mountains were formed. Mars has a similar planet structure with a crust, mantle, and a core. The lack of plate tectonics, however, led to the creation of much higher mountains.
Tharsis is a volcanic province on Mars, hosting many of Mars’s mountains and volcanoes inside and near the area.
Mars has water ice at the poles, and Mars’s mountains and planet structure are somehow similar to the Earth. Perhaps Mars also used to have liquid water running on the surface.
