The geological history of Mars is incredibly complex, and we really don’t know much about it. What we do know right now is based on a limited number of tiny fragments of a much larger story, with those fragments allowing scientists to only make educated guesses on how they fit together.
Many of those guesses will certainly turn out right. Just as many will turn out wrong. At this moment in our exploration of the Red Planet we can only grasp at straws while always keeping an open mind, as later data is surely going to change any conclusions we presently have.
The photo to the right is a good illustration of this struggle. Rotated, cropped, and reduced to post here, it was taken on September 27, 2020 by the high resolution camera on Mars Reconnaissance Orbiter (MRO), and shows what at first glance looks like a stream of white frost or ice descending down a canyon to the south.
That first impression however is entirely wrong. When I asked Chris Okubo of the U.S. Geological Survey, who requested this image from MRO, what it was, he explained,
The white material is not frost. Instead, these are sedimentary rocks comprised primarily of sulfates. The texture to me suggests these are lithified dunes.
Lithified merely means that the dunes have hardened into rock. Sulfates are a salt formed from sulfuric acid, and are on Mars often linked to some complex mineralogy. If you stood there the colors would be white and red, quite beautiful. As Okubo explained,
The sulfates are white to tan in color, but there would also be a lot of red/brown Mars dust on top of it. It would be similar to walking around some of the playas in the desert southwest.
Though these white sulfate deposits have their root in sulfuric acid, Okubo added that they “are in the form of minerals similar to gypsum and so they would be safe to touch.”
What is going on here? As is usually the case, we need to first take a wider view to get some context.
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