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Cool image time! The photo to the right, cropped to post here, was taken on February 26, 2021 by the high resolution camera on Mars Reconnaissance Orbiter (MRO) of a small section of the floor of 85-mile-wide Galilaei Crater.
The main focus of the image is the polygonal cracks that cover the flat low areas of the crater floor, interspersed randomly by small mesas and shallow irregular depressions. The depression in this particular image is especially intriguing. It to me falls into my “What the heck?!” category, for I can’t imagine why among this terrain of polygons and pointed mesas there should suddenly be an irregularly shaped flat depression with a completely smooth floor that has no cracks at all.
The polygons are less puzzling. Galilaei Crater is very old, its impact thought to have occurred about 4 billion years ago. Though it sits at 5 degrees north latitude, practically on the Martian equator and thus in what is now Mars’ most arid region, scientists believe that once there was a lot of liquid surface water here. The overview map below illustrates this.
This map, annotated slightly to post here, comes from figure 3 in a 2019 paper that proposed, based on existing data and simulations, that once catastrophic floods had burst forth from the giant canyon Valles Marineris to the west to form the intermittent oceans shown on the map. The white dot in Galilaei Crater marks the location of today’s image.
When this region was wet, the floor of Galilaei Crater was likely also wet, with its own short-lived lake. When that lake dried away, the cracks formed. As explained in an 2010 paper,
We propose desiccation to be a dominant mechanism for the formation of Crater Floor Polygons without ruling out thermal contraction as a possible contributor in some cases. This implies that lakes or water-rich sediments occupied the craters in the past.
On Earth such polygons are frequently seen in mud flats after the water has evaporated away. The mud as it dries contracts, and cracks to form the polygons.
The greenish-blue color of the terrain in the color strip suggests [pdf] a coarse material of sand or rocks, though I am not certain this is entirely correct. The tiny mesas in the depression are light reddish and tan, suggesting those mesas are covered by dust and fine-grained sand. Why the polygons and the floor of the depression have little dust (assuming my interpretation of the colors is correct) while the surrounding flats do not is most baffling.
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.
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.