My Findings
The Image Data Chronology
Not long after landing, the Opportunity rover found the area strewn with literally tens of thousands of small spheres, most measuring between 1 and 5 millimeters in diameter, with an average size of 3 millimeters. After the color images were processed, the spheres appeared slightly bluer than the surrounding rocks and sand. They were promptly named "blueberries" by NASA staff.
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Here is a color
image from the Opportunity panoramic cameras. Note the even
distribution of these spheres. They are slightly blue (although not
much) and might well be made of a mineral known as siderite, or iron
carbonate.
This is interesting because siderite and hematite are often closely located due to their formation conditions being quite similar. Hematite presence was a major reason for Opportunity landing in this area, knows as "Meridiani Planum". Ancient fossils here on earth used iron quite commonly and they are responsible for laying the "red earth" that is used as iron ore today. Later fossils depended more heavily on calcium and that is where calcium carbonate comes from to make limestone and marble. Image credits go to Keith Laney for creating these beautiful, true-color renditions from the raw NASA image data. The full sized picture is here: http://www.keithlaney.com/OCI/O7.jpg |
Soon after finding these spheres, the microscopic imager was used to try and determine what they were and where they came from. The leading theories were that they were lapilli (volcanic ash "droplets"), or perhaps they were molten rock that had been blown from a volcano and hardened into spheres in flight as they cooled, or that they were the droplets of molten rock that had been created in a meteorite impact. Some also felt that they might be "concretions", a form of rock made when water dissolves some minerals and grows little beads in a manner similar to the formation of a pearl in an oyster, but without the action of biology.
The lapilli explanation was soon shot down because these spheres were seen in the rock itself. Note that the spheres are tougher than the surrounding rock because erosion eats the rock away but not the spheres. This means that they are very unlikely to be volcanic ash, which would be softer and erode easily.
| It was soon clear
that these rocks were layered, and many felt that they were sedimentary-
formed by layers under water. Imagine sand and silt falling to the
bottom of a pond and being compressed under immense weight for many
thousands or millions of years.
Some NASA scientists stated that these were most likely layers of volcanic ash, and not related to water at all. But other images show that these "ashfalls" had to recur clearly at regular intervals for a very long time to explain the uniform and regular spacing of the layers. To the geologist, these look very much like water-created formations, like the layers of mud from a lake bottom. Furthermore, the layering would be explained by seasonal or climatic variations, exactly like we find here on Earth. The full-sized image is available here: http://www.keithlaney.com/OCI/G1.jpg |
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