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Knobs on the floor of a Martian caldera

Knobs on the floor of a Martian caldera
Click for original image.

Cool image time! The picture to the right, rotated, cropped, reduced, and sharpened to post here, was taken on February 14, 2023 by the high resolution camera on Mars Reconnaissance Orbiter (MRO) and shows what the scientists have dubbed as “enigmatic knobs” located on the caldera floor of a Martian shield volcano.

The knobs themselves, while puzzling, aren’t that interesting on their own. They are no more than 100 to 200 feet high, and are relatively featureless. Since most lack a pit at their peaks, they are probably not some form of small volcanic vent, though this conclusion is uncertain. The location, at about 30 degrees south latitude, suggests the faint possibility of near surface ice, which could make these mud volcanoes, or a very specific Arctic-type permafrost mound dubbed pingos, but once again the lack of any central pit at their peaks makes these origins also doubtful.

What the knobs however revealed to me was a giant Martian shield volcano I had never noticed before, even though it was hiding in plain sight.

Overview map

The red dot on the overview map to the right marks this location, inside the caldera of the shield volcano Hadriacus Mons. Martian shield volcanoes tend to be relatively flat, as their lava flows out slowly over a long time, covering a wide area. In the case of Hadriacus, it is so flat that I never noticed its existence previously on the upper slopes leading down into Hellas Basin, the death valley of Mars. And yet, it is almost three hundred miles across, with a caldera forty miles wide standing more than 50,000 feet above the floor of Hellas.

The many drainage channels flowing down its southwest flanks into Hellas are thought [pdf] to have been formed by a combination of volcanic, fluvial, and catastrophic flood events, all taking place more than 1.4 billion years ago. Strangely, none of these drainage channels flow into DaoValles. Instead, they drain directly into the floor of Hellas to the west of Dao.

Moreover, in recognizing the existence of Hadriacus the origins of Dao Valles come into focus. While it is appears to be filled with glacial features today, its sudden beginning on the flanks of Hadriacus suggests it might have originally formed as a volcanic vent and lava tube, which was subsequently carved wider with its roof removed by ice/liquid water processes.

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 are available at Amazon, Barnes & Noble, and all book vendors, with the ebook priced at $5.99 before discount. The ebook can also 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.


Autographed printed copies are also available at discount directly from me (hardback $24.95; paperback $14.95; Shipping cost for either: $5.00). Just email me at zimmerman @ nasw dot org.

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