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Cracks, chaos, and maybe caves in one place on Mars

Mosaic of Avernus Cavi fissures
Click for higher resolution. Original images found here and here.

Today’s cool image to the right is a mosaic I have made from two images taken by the context camera on Mars Reconnaissance Orbiter (MRO), showing a most intriguing region on Mars dubbed Avernus Cavi, located in the large volcanic plain called Elysium Planitia between the giant volcanoes Elysium Mons and Olympus Mons, a region I like to call Mars’ volcano country.

The mosaic shows in one picture much of the typical terrain in Avernus Cavi. We see many linear depressions or cracks, created when the ground stretched and cracked at weak points. We also see many depressions that suggest sinkholes, places where the surface sagged down because of a void below ground.

The area of knobs and mesas in the picture’s southeast quadrant is very typical Martian chaos terrain, the later result of long term erosion of these cracks and depressions.

The white box shows the area covered by the image below.

Closeup of fissures
Click for full image.

The photo, cropped and reduced to post here, covers a section of a March 2020 MRO high resolution picture of these cracks, posted today as that camera’s picture of the day. The short caption:

This image features small collection of cave candidates in Avernus Cavi, located in Elysium Planitia. These candidates are located at the base of scarps formed by extensional fracturing. We might be able to resolve rim and floor textures as finely as possible to verify if any caves are indeed present.

In other words, no cave entrances have as yet been identified, but scientists are taking high resolution images in an effort to find them. The assumption is that the cracks and fractures are much deeper than what we can see on the surface, and that there are likely voids below.

The black rectangle in the mosaic above shows the area covered by another MRO high resolution image, taken in 2015 and labeled “Lines of Pits in Avernus Cavi Region.” What struck me about that image was how much the depressions appear to reflect a river tributary system. This is not we are looking at, but that’s what it invokes. Like the first picture above, the cracks occur because the land has become stretched, opening up fissures along fault lines.

Overview map

As shown by the red cross in the overview map to the right, Avernus Cavi is located within the huge volcanic ash deposit called the Medusa Fossae Formation, thought to be the source of most of Mars’ dust. This is also at the Martian equator, so the surface in this region is very dry, with most features the result of some volcanic process.

It is also relatively close to the majority of the quakes detected by InSight, suggesting that such cracks and fissures could still be spreading and shifting.

Conscious Choice cover

Now available in hardback and paperback as well as ebook!


From the press release: In this ground-breaking new history of early America, historian Robert Zimmerman not only exposes the lie behind The New York Times 1619 Project that falsely claims slavery is central to the history of the United States, he also provides profound lessons about the nature of human societies, lessons important for Americans today as well as for all future settlers on Mars and elsewhere in space.

Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space, is a riveting page-turning story that documents how slavery slowly became pervasive in the southern British colonies of North America, colonies founded by a people and culture that not only did not allow slavery but in every way were hostile to the practice.  
Conscious Choice does more however. In telling the tragic history of the Virginia colony and the rise of slavery there, Zimmerman lays out the proper path for creating healthy societies in places like the Moon and Mars.


“Zimmerman’s ground-breaking history provides every future generation the basic framework for establishing new societies on other worlds. We would be wise to heed what he says.” —Robert Zubrin, founder of founder of the Mars Society.


All editions available at Amazon, Barnes & Noble, and all book vendors. The ebook can be purchased direct from my ebook publisher, ebookit, in which case you don't support the big tech companies and I get a bigger cut much sooner. Note that the price for the ebook, $3.99, goes up to $5.99 on September 1, 2022.


Autographed printed copies are also available at discount directly from me (hardback $24.95; paperback $14.95). Just email me at zimmerman @ nasw dot org.


  • I hardly ever comment on them because I have nothing to add, but these Mars pictures and explanations are the biggest reason I visit this site. Just so you know.

  • markedup2: Thank you. I often wonder if there really is a lot of interest in these cool images, as the number of comments are always far less than the political posts.

    Not that it matters. Everything I do on BtB is because it is something that interests me. Which means I will keep posting them, because I enjoy it and doing so gives me some relief from the truly depressing news of the day.

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