Inverted Features on Mars

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Imagine a river or lake on Earth. What would it look like if you took all the water out? Something like this:

Dry Riverbed in the Himalayas

On Earth, when a riverbed dries out it leaves a depression, or indentation in the Earth.


So then why on Mars are riverbeds and lakes inverted, or raised features, like in the below image of Gorgonum Basin?




Gorgonum Basin. Credit: HiRISE (Click through for HiRISE captioned image)

or Iani Chaos?



Iani Chaos. Credit: THEMIS (Click through to post on this image)

It all comes down to erosion. The weight of the water condenses and compacts the sediment beneath it, making it much harder and more resistant to wear from erosion. Thus, over the course of millions (and sometimes billions) of years, the ground surrounding the river bed gets eroded much more rapidly than the riverbed itself. This results in the inverted features that you see on Mars today.

Mars Photo of the Day - 30 Sep 2012

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Today's Image of Mars was taken by MSL Curiosity; it shows further evidence that water once existed on Mars. What you see here are remnants of an ancient riverbed on Mars, including the prominent rock outcrop Hottah, named after Hottah Lake in Canada's Northwest Territories.

Click to see full size original
Source: NASA/JPL

This rock outcrop is a sedimentary conglomerate, meaning that it is comprised of small fragments cemented together. The outcrop is tilted up due to some sort of disruption, most likely as a result of nearby impacts and their associated tremors.

We can tell that this used to be an ancient stream because of the size and rounded shape of the small rocks/gravel and the fact that small bits of the gravel and sand sized grains are cemented into the outcrop. Because some of the cemented gravel is round and too large to have been transported by the wind, scientists believe that it was transported by fast moving water, which is further evidence for this once having been a stream/river.

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The View From MSL Curiosity's Gale Crater Landing Site

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As Mars Science Laboratory looks around its landing spot in Gale Crater, what does it see? This! 

You need to click on the image to see it in magnificent high resolution! Just looking at it you can see that the terrain looks very similar to something you might see in the southwestern United States. This mosaic combines 79 different images taken by MSL's Mastcam since the rover's arrival on Mars. The black overlays you see are areas that were unable to be processed or which were lost during transmission back to Earth.

What can we see of note in this image?

We can see the area excavated by the blast of MSL's descent stage engines. Of most interest to scientists is the uppermost layer of fine material embedded with rock fragments. The characteristics of the exposed sediments will tell scientists a lot about the conditions under which they formed and will give them a greater understanding of the past Martian environment.

In the mosaic you can also see the rim of Gale Crater about 18 km north of MSL. There you can see where a network of valleys are thought to have entered into Gale Crater in the distant past.

This is actually the first time that a river system has been imaged from the surface of Mars! MSL will not be investigating this particular fluvial system because it's main target, Mount Sharp, is to the south, but the images it provides from this distance are still the most detailed images we have and will tell us a lot about Martian river systems!

In the days and weeks to come there will be much more to discover about Gale Crater! Keep checking back for the latest and greatest!

Mars Photo of the Day - June 6 2012

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Today's Image of Mars is a picturesque example of what became of the rivers on Mars and the effects those ancient bodies of water had on the surface. You can see in this image that much of the terrain is composed of light and moderately toned layered material. The cratered, lower elevation areas tend to be darker.

Clicking on this image will take you to the original high resolution one from HiRISE. [See their caption]

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Mars Photo of the Day - Jan 16 2012

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Today's Image of Mars once again shows Iani Chaos, but this time we can see all the intricate features  created by the massive amount of water that once passed through the area. Iani Chaos was the source for the large outflow channel, Ares Valles after geologic faults ruptured an enormous reservoir of ground water, causing it to flood the surface.

Two Mars orbiters (Mars Global Surveyor and Mars Express) have found mineralogical evidence that there was once an abundance of water in Iani Chaos, lending credence to the idea that the features below were formed by water. The two Mars orbiters found hematite and gypsum in the area, two minerals that are only known to be formed in the presence of an abundance of water.

But how did all these features form?

Looking at the image you can see many web-like features created by what look like inverted riverbeds. Once active rivers on Mars deposited sediments, which were more wear-resistant than the surrounding terrain. When Mars dried up these sediments remained. Over billions of years the wind on Mars eroded the landscape, but the hardened sediments were harder than the surrounding terrain so they became less eroded, thus the reason you see this web of features.

But where did these rivers come from?

When geologic faults ruptured an underground reservoir, millions of tons water poured out onto the surface. The water took the easiest way out, following natural features and creating what we see here today. 

You can see in the bottom right of this image that the terrain is about as high as the inverted riverbeds we see elsewhere. I think we can safely assume from this that there was an enormous presence of water at the bottom right of this image, which drained through the interlocking riverbeds we see below. While this is just an educated guess, these same features are common on Earth, where great lakes and seas have channels and rivers feeding into and out of them.

 Clicking on this image will show the larger size. To see the THEMIS article this image came from

Source: THEMIS

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Mars Photo of the Day - Dec 9 2012

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Today's Image of Mars shows an inverted, winding, riverbed surrounded by features called yardangs. 

Yardangs are created when the primary form of erosion is wind. They are easy to identify as they have multiple sharp ridges that are oriented in a similar way: a result of wind erosion over millions of years. 

But why is the riverbed raised? Shouldn't it be carved into the surface?

When the river was flowing it deposited layer after layer of sediments, which were harder than the surrounding terrain. Since the river dried up the whole area has spent millions of years being eroded by wind. Because the sediments deposited by the river bed were harder than the surrounding terrain they were eroded much less than the rest of the surface, thus the reason the river bed is inverted.

Today's image was taken by HiRISE. Clicking on the image will take you to the original captioned image from them!

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