Mars has been in the human consciousness since pre-historic times, and can easily be seen as noticeably red with the naked eye as a result of iron oxides in its surface material. At its closest approach, Mars is just 33.9 million miles (54.6m kms) from Earth, and 249 million miles (401m kms) distant at its furthest, but even though the “Red Planet” is covered with impact craters, valleys, deserts, polar ice caps, canyons, and volcanoes, very few of its features are visible to amateur astronomers.
A 4-inch telescope using 150 times magnification, for instance, will reveal its colorful orange disk, polar ice caps, and large dark region crater fields, such as Syrtis Major, while a 6 to 8-inch scope will show significantly more surface detail, and possibly some atmospheric clouds, but the planet is notoriously hard to observe, and almost all of what we known about Mars today is due to images taken by, and experiments carried out, almost in-situ by high-tech probes and rovers. As a result, it is only relatively recently that we have come to appreciate the complexity of the processes that have made the planet into what it is today.
Thus, to compile 10 of the most interesting features of this planet is no easy task; however, the items presented here represent some of the biggest, tallest, and longest features of their type in the entire solar system, as well as some of the smallest, prettiest, and most unexpected features on this weird and wonderful planet. Our hope is that you enjoy this selection, and that at least some of them will be new to you. The image at the top of the page shows a topographic map of Mars, and will help to locate some of the features mentioned. Its most obvious features include the mostly flat, low-lying northern lowlands and Vastitas Borealis region; the elevated Tharsis Rise along with its four prominent volcanoes, including Olympus Mons; and the mountainous southern highlands, which is between 1 to 3 km higher than its northern counterpart.
Martian Ice Caps
Object type: Ice Caps
Discoverer: North Cap by Giovanni Domenico Cassini (1666),
South Cap by Christiaan Huygens (1672)
For a relatively dry planet, Mars sports two very impressive polar ice caps, both of which contain huge amounts of primarily water ice. During the northern pole’s winter, it also accumulates a thin layer of frozen carbon dioxide about one metre thick, while at the southern cap it has a permanent dry ice covering around 8 meter thick.
The south polar cap usually spans about 217 miles (350 km) with a total thickness of about 1.8 miles (3 km), and contains about 25%-30% of the planets’ atmosphere in the form of frozen carbon dioxide. Copious amounts of water are then released when it sublimes in the Martian summer, forming vast cirrus clouds in the process.
The north polar ice cap shown in the image, on the other hand, spans about 600 miles (1,000 km), and has an average total thickness of about 1.2 mile (2 km). This translates into a volume of about 1.6 million km3 of ice, in comparison to the volume of ice in the Greenland ice sheet, for instance, which is about 2.85 million km3 of ice.
Object type: Lowland Plain
Location: North Pole
Coordinates: 70.5°N | 103°E
Vastitas Borealis (“northern waste”), the largest lowland region on Mars, lies 2.5 to 3.1 miles (4–5kms) below the mean planetary elevation, and surrounds the planet’s north polar region. The image opposite shows an area of the Vastitas Borealis encircling the North Pole (left), with the large crater situated top right being the Korolev Crater, which is 53 miles (85 kms) wide.
According to the Mars ocean hypothesis, it has a 4.1–3.8 billion year old southern shoreline that runs the length of Mars, except through the 4,000 km wide Tharsis volcanic region, and is therefore seen as being a good location to search for water related sedimentary microbial life. Supporting this controversial theory is the northern martian surface being less heavily cratered than in the southern hemisphere, as well as shoreline-like geographic features, and the northern plains being lower than in the southern hemisphere, just like the ocean basins back here on Earth. It has also been speculated that this ancient ocean covered two-thirds of Mars, but would have frozen as the Martian climate cooled, and either retreated beneath the flat northern plain, or perhaps lost to the atmosphere and then space.
Coordinates: 13.9°S | 59.2°W
Length: over 2,500 miles (4,000 km)
Width: 120 miles (200 km)
Depth: 4 miles (7 km)
Discoverer: Mariner 9 (1971)
Named after the Mariner 9 orbiter that discovered it in the early 1970’s, this vast crack in the surface of Mars runs for more than 2,500 miles (4000 km), or nearly 25% of the equatorial circumference of the planet. On average, the chasm is 120 miles (200 km) wide, and up to 23,000 ft (7 km) deep, which makes it the biggest such feature in the solar system, bar some of the rift valleys on Earth.
Starting at the edge of the Tharsis Montes volcanic plateau region to its west, this feature is believed by planetary scientists to have been caused by a thickening of the planet’s crust when a massive plume of lava rose, lifting the entire Tharsis Montes region above the local terrain, hence the region’s alternative name, Tharsis Bulge. Nonetheless, there is some evidence to suggest that the chasm was widened by various forms of erosion subsequent to its formation, and even that the main channel may have been cut by extensive lava flows from Pavonis Mons, another of the huge volcanoes directly to the west of the canyon.
Object type: High Lava Plain
Height: 7 km (excluding volcanoes)
Width: 5,000 km
Area: 10–30 million km2
Discoverer: Mariner 9 (1971)
The Tharsis Rise (Tharsis Bulge) is a vast elevated region of terrain that covers 25% of the planet’s surface area south of the equator on the western side. It is marked by four volcanoes which make up the region (Ascraeus Mons, Pavonis Mons, Arsia Mons, and Olympus Mons), with this image showing the close relationship between the bulk of the Tharsis Montes region and the Vallis Marineris. The three volcanoes to the right of Olympus Mons, spaced around 430 miles (700 km) apart, are located on the crustal bulge’s crest, and are thought by some investigators to have contributed directly to the formation of Vallis Marineris, whose westernmost channels can be seen to terminate (or start) in the lava flows from the volcanoes.
Object type: Shield Volcano
Coordinates: 18.65°N | 226.2°E
Age: 100 million years
Height: 16 miles (25 km)
Diameter: 374 miles (624 km)
Discoverer: Mariner 9 (1971)
This image of Mars was taken by the Viking 1 spacecraft in 1987, and it shows a clear view of the volcanic plateau of Tharsis Bulge, also known as Tharsis Montes, which is dominated by the monstrous and aptly named volcanic mountain, Olympus Mons, just above centre. With a peak 16 miles (25km) high, Olympus Mons towers above the tenuous Martian atmosphere, and is the planet’s tallest mountain. Olympus Mons may also be the tallest mountain in the solar system, although figures on its height vary slightly and it may have competition in the form of Rheasilvia Mons, a mountain on the asteroid Vesta.
Viewed in relief, the base of Olympus Mons appears to have been cut out with a cookie-cutter, with edges that rise 6 miles (9.6 km) above the local terrain, a full half-mile higher than the tallest peak on Mt. Everest, which rises only 5.5 miles (8.8 km) above sea level. Despite having been dormant for millions of years, planetary scientists are divided on whether Olympus Mons is still active, although most agree that its last activity took place somewhere between 20 million and 200 million years ago.
Syrtis Major Planum
Object type: Albedo feature
Coordinates: 8.4°N | 69.5°E
Dimensions: 930 x 620 miles (1,500x 1,000 km)
Peak: 3.7 miles (6 km)
Discoverer: Christiaan Huygens (1659)
Discovered and documented by Christiaan Huygens in 1659, this albedo (“dark spot”) feature was the first surface feature on another planet to be discovered and documented. Spanning an area of 930 miles (1,500 km) from north to south, and 620 miles (1,000 km) from east to west north of the planets’ equator, it was first thought to be a plain, but the feature is in fact a low-relief shield volcano composed of basaltic volcanic rock that rises to an elevation of only 3.7 miles (6 km), which explains the area’s dark coloration and relative lack of red dust. The feature is big enough for Huygens to have used it to estimate the length of the Martian day in the 17th century. While early observers knew the feature by different names at different times, Giovanni Schiaparelli eventually named the area “Syrtis Major” when he drew a map of the planet during its close approach in 1877.
Utopia Planitia Frozen Lake
Object Type: Frozen Water Lake
Location: Utopia Planitia region
Discoverer: Mars Reconnaissance Orbiter
Spotted by the ground-penetrating Shallow Radar (SHARAD) instrument aboard NASA’s Mars Reconnaissance Orbiter (MRO), this vast field of undulating terrain overlies a supply of frozen water that is bigger in extent than the US state of New Mexico, or some European countries. While the vertical relief in this image is greatly exaggerated, it is typical of the type of terrain that overlies large sheets of ice, such as has been found in Canada and elsewhere. In this case, the ice lies at depths of between 3 and 33 ft (1 to 10 m) and extends to depths of between 260 ft and 560 ft (79 m to 170 m) below the surface. Although the ice deposit contains about 15% dirt and rocks, the water content is about equal to that of Lake Superior in the US, which holds around 2,900 m3 (12,090 km3) of water.
Mars currently has an axial tilt of 25 degrees, resulting in large amounts of water ice accumulating at its poles. The vast underground frozen water deposit recently discovered is believed to have formed during a period in the planet’s history when the its axis was more tilted, and snowfall accumulated into an ice sheet in this region now halfway between the equator and the north pole.
Proctor Crater Ripples
Object type: Sand Dunes
Location: Proctor Crater
Coordinates: 48°S | 330.5°W
While the polygonal shapes in this picture might look like a piece of coral in a tidal pool, it is in fact a network of intersecting sand dunes in the bottom of the Proctor Crater, which is 104.5 miles (168.2 km) in diameter. Spotted by the Mars Reconnaissance Orbiter that can resolve objects as small as a meter on the surface, these dunes were snapped from an altitude of 157.8 miles (252.4 km) when the Sun was at an angle of about 53° above the horizon.
In this particular image, the resolution is about 59 inches (152 cm) per pixel, but note that there are no blue or purple sand dunes on Mars. The blue ridges on the dunes are the result of image enhancement processes that allow investigators to differentiate easily between elevations, textures, and angles of illumination in images taken by the HiRISE (High Resolution Imaging Science Experiment) camera on board the orbiter.
Object type: Travelling Sand Dune
Location: Gale Crater
While the sand dune in this image appears to be hundreds of feet high, it is in fact only about 13 to 17 ft (4-5m) high, but what it does show is the processes by which dunes in the “Bagnold Dunes” field migrate by as much as 3 ft (1m) per Earth year. These dunes are found climbing up the northwestern flank of Mount Sharp located at the centre of the Gale Crater.
In this composite image taken by the Curiosity rover on its 1,200th Martian day on the planet, sand can be seen pouring down the downwind side of one of the many dunes that comprise the Bagnold field, in this case the “Namib Dune”, which has an angle of between 26 and 28 degrees, a much steeper angle than the opposite face of the dune. In this process, sand is driven up the upwind slope to cascade down the steep, downwind slope, in exactly the same way sand dunes in the Namib Desert in southern Africa cover great distances. In effect, the dunes’ sand is carried over itself, but because Mars’ atmosphere is very much thinner than Earth’s, the winds on Mars are not as powerful, so the process takes longer.
Fresh Impact Craters
Object type: Craters
Cratering on Mars happens relatively frequently, and investigations suggest that new craters bigger than about 12.8 ft (3.9 m) are formed at a rate of about 200 or so per year. In 2017, for instance, the Mars Reconnaissance Orbiter using its HiRISE (High Resolution Imaging Science Experiment) camera, discovered a 650 ft (200m) crater with its central impact measuring a few meters across. It is believed to have formed between 2014-2016, making it one of the youngest known craters on the planet
Another impressive and recent 100-ft (30-m) wide crater is shown in the image, and is believed to have been formed sometime between July 2010 and May 2012. The ejecta rays (debris scattered outwards) stretch for about 9.3 miles (15 km), and their arrangement suggests that the impactor had hit the surface at, or close to a 90-degree angle. However, Mars is not really blue below its coat of red dust- the blue in this image is the result of an enhancement process to highlight the ejecta pattern.
Foreign Object on Mars
Object type: Meteorites
In 2005, the Opportunity rover discovered the first meteorite on Mars, named “Heat Shield Rock,” while in May 2014, Curiosity rover found the largest Mars meteorite to date called Lebanon, with this iron-rich meteorite measuring around 7 ft (2m), with two smaller companions located nearby.
While the Curiosity rover has since snapped many weird and wonderful objects in its travels across the Martian surface over the years, the golf-ball-sized object shown in the image is of some scientific interest. When the rover spotted it, it zapped it with a powerful laser, and by analyzing the resulting vapor, the instruments on the rover determined that the object is a nickel-iron meteorite that fell out of the Martian sky. Named “Egg Rock”, the object’s exact origin is still unknown, but is likely to have formed the molten core of an asteroid. If nothing else, though, zapping it with its onboard laser proved that the rover’s laser-firing “ChemCam” instrument was working as expected.