Planets

This Is an Ancient Meandering River... On Mars

There are few more potent reminders that Mars used to be a wet world than seeing ancient, dried up river beds etched into the red planet's surface.

There are few more potent reminders that Mars used to be a wet world than seeing ancient, dried up river beds etched into the red planet's surface. Although this particular example has been weathered by hundreds of thousands or even millions of years by Mars' weak winds, its beautifully preserved channel is telling us a story.

MORE: Mind-Blowing Beauty of Mars' Dunes: HiRISE Photos

Located in Acidalia Planitia, a region dominated by a plain north of the Martian equator, this river apparently flowed from right to left, down the slope of a crater rim and into the crater itself. This image was captured by the prolific High-Resolution Imaging Science Experiment (HiRISE) camera aboard NASA's Mars Reconnaissance Orbiter (MRO) on Sept. 25, 2015.

It is not known how long the water flowed in this ancient river, nor its source, only that liquid water channels converged to rush down the crater rim, meandering into the plain below. This particular "dendric" river channel is composed of many smaller tributaries that fed the primary channel, according to Mike Mellon of the HiRISE team.

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It is not fully understood how rivers such as these were sourced - whether by sub-surface aquifers, meltwater or even rainfall - but through studies of the long-lost rivers of Mars from orbit we can supplement studies by surface missions (such as NASA's Mars rovers Curiosity and Opportunity) to help us piece together the puzzle of Mars' wet past.

Source: HiRISE/Univ. of Ariz.

The High Resolution Imaging Science Experiment (HiRISE) camera is the most powerful imager in orbit around Mars. Capable of resolving objects less than a meter wide on the surface of the Red Planet while attached to NASA's Mars Reconnaissance Orbiter (MRO), HiRISE has brought us unparallelled views of Martian landscape, geology, active erosion processes and even our own surface missions.

After nearly 8 years of orbiting Mars, HiRISE has amassed a huge archive of observations and, in many cases, observations can be combined to provide a unique insight to the planet's topography -- an observation that can be difficult to make with a single top-down snapshot.

Therefore, the HiRISE team use "stereo pairs" of observations from different orbital passes (and therefore different viewing angles) of the same locations on the Martian surface. This can produce topographical maps of surface features accurate to within 10s of centimeters in height. These high resolution digital terrain models, or DTMs, provide an incredible scientific insight as well as constructing an aesthetically pleasing perspective of an otherwise "flat" vista. In all images a color spectrum of purple-white is used, where the purple/blue hues are the lowest lying land and the red/white hues are the highest. Here are some of our favorite DTM images.

Shown here are the stunning "moving dunes" of Nili Patera (catalog number: ESP_017762_1890)

Elevation range: 55 meters (purple/blue - lowest) to 275 meters (red/white - highest) above mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=ESP_017762_1890

DTMs can be very useful when trying to understand the morphology of craters on the Martian surface. This is Raga Crater, featuring very steep crater slopes in its interior (ESP_014011_1315).

Elevation range: 1,311 meters (purple/blue - lowest) to 1,966 meters (red/white - highest) above mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=PSP_006899_1330

This is one of the stereo pairs of images used to compose the DTM of Raga Crater (see previous slide). Although this HiRISE image provides incredible high-resolution imagery of the feature, there is little elevation data, something the DTM provides through its topographical color spectrum (ESP_014011_1315).

Source: http://www.uahirise.org/ESP_014011_1315

The rim of Endeavour Crater in Meridiani Planum. Since 2011, Mars rover Opportunity has been extensively studying the crater's rim, turning up exciting evidence of past water on the Martian surface. The HiRISE DTMs have played a key role in mapping the rover's drive in the region (ESP_018701_1775)

Elevation range: -1,695 meters (purple/blue - lowest) to -1,380 meters (red/white - highest) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=ESP_018701_1775

The barchan dunes on Mars can be monstrous structures. This example is nearly 300 meters high and features a steep slip face where there appear to be obvious signs of avalanches having taken place (PSP_006899_1330).

Elevation range: 1,031 meters (purple/blue - lowest) to 1,321 meters (red/white - highest) above mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=PSP_006899_1330

This may look like a shooting star cartoon, but it's actually an old impact crater plus ridge of dunes in Athabasca Valles. The "tail" of material is likely caused by prevailing winds shaping the landscape (PSP_002661_1895).

Elevation range: -2,611 meters (purple/blue - lowest) to -2,441 meters (red/white - highest) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=PSP_002661_1895

Victoria Crater in Meridiani Planum, a crater explored by Mars Exploration Rover Opportunity from September 2006 to August 2008 (PSP_001414_1780).

Elevation range: -1,453 meters (purple/blue - lowest) to -1,373 meters (red/white - highest) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=PSP_001414_1780

Small cones in an ancient volcanic region of mars, formed by molten lava flowing over ice or water (ESP_018747_2065).

Elevation range: -3,262 meters (purple/blue - lowest) to -3,196 meters (red/white - highest) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=ESP_018747_2065

A deep channel formed by the ancient flow of water in the Tartarus Colles Region. A small island is evident in the meandering channel (ESP_012444_2065).

Elevation range: -3,301 meters (purple/blue - lowest) to -3,189 meters (red/white - highest) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=ESP_012444_2065

Zooming in on Gasa Crater reveals gullies formed through erosion (ESP_021584_1440)

Elevation range: -704 meters (purple/blue - lowest) to 581 meters (red/white - highest) above mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=ESP_021584_1440

The "inverted valleys" near Juventae Chasma were once the floor of valleys. But over time, the topographic low regions, which are composed of material resistant to erosion (likely cemented there by water sedimentation), become ridges as the softer material around them eroded below the ancient valley floors (PSP_007627_1765).

Elevation range: 2,128 meters (purple/blue - lowest) to 2,234 meters (red/white - highest) above mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=PSP_007627_1765

A well-preserved 3 kilometer-wide impact crater (ESP_012991_1335).

Elevation range: 1,114 meters (purple/blue - lowest) to 1,742 meters (red/white - highest) above mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=ESP_012991_1335

A mound in Ganges Chasma. Using the topographical color reference, this feature is approximately 800 meters high from base to peak. The arcing structure around the mound may be a wind-blown ridge of material surrounding the obstacle (ESP_017173_1715).

Elevation range: -3,716 meters (purple/blue) to -2,711 meters (red/white) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=ESP_017173_1715

Inside a crater in Western Arabia Terra with stair-stepped hills and dunes.

Elevation range: -2,575 meters (purple/blue) to -2,259 meters (red/white) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=PSP_002047_1890

A fresh impact crater. Newly formed craters on Mars have smooth ridges and are often circular. Older craters undergo atmospheric erosion processes, often causing the ridges to appear broken, frayed and slumped (PSP_005837_1965).

Elevation range: -4,304 meters (purple/blue) to -3,658 meters (red/white) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=PSP_005837_1965

Layered surface deposits of material in the north polar region of Mars leave a step-like pattern (ESP_018870_2625).

Elevation range: -3,555 meters (purple/blue) to -3,027 meters (red/white) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=ESP_018870_2625

A deep fissure scars the Martian surface, a possible source of ancient floodwater (PSP_010361_1955).

Elevation range: -2,747 meters (purple/blue) to -1,577 meters (red/white) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=PSP_010361_1955

At the base of shield volcano Ascraeus Mons' slopes in the Tharsis Region, ancient river and tributary channels carve up the landscape (PSP_002486_1860).

Elevation range: 6,432 meters (purple/blue) to 6,675 meters (red/white) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=PSP_002486_1860

A distributary channel -- a river that branches off and flows away from a main channel -- can be seen flowing down the base of Ascraeus Mons (ESP_011373_1865).

Elevation range: 6,568 meters (purple/blue) to 6,766 meters (red/white) below mean Mars surface elevation.

Source: http://www.uahirise.org/dtm/dtm.php?ID=ESP_011373_1865

To see the full collection of HiRISE Digital Terrain Models, browse the HiRISE web archive.