The Sinus Sabaeus quadrangle is one of the 30 quadrangle maps of Mars created by the United States Geological Survey (USGS) Astrogeology Science Center. It is designated as MC-20 (Mars Chart–20). The Sinus Sabaeus quadrangle spans the region from 315° to 360° west longitude and 0° to 30° south latitude. It includes the prominent Schiaparelli Crater, a large, easily recognizable impact feature located near the Martian equator. The quadrangle also encompasses portions of the ancient, heavily cratered terrains of Noachis Terra and Terra Sabaea. The name "Sinus Sabaeus" derives from a classical albedo feature named after an incense-producing region south of the Arabian Peninsula, near the Gulf of Aden.
Layers Wislicenus Crater and the Schiaparelli basin crater contain layers, also called strata. Many places on Mars show rocks arranged in layers. Sometimes the layers are of different colors. Light-toned rocks on Mars have been associated with hydrated minerals like sulfates. The Mars rover Opportunity examined such layers closely with several instruments. Some layers are probably composed of fine particles because they appear to break up into fine dust. Other layers break up into large boulders, suggesting they are much harder. Basalt, a volcanic rock, is thought to be present in the layers that form boulders. Basalt has been identified in many locations on Mars. Instruments on orbiting spacecraft have detected clay (also known as phyllosilicates) in some layers. Scientists are excited about finding hydrated minerals, such as sulfates and clays, on Mars because they are usually formed in the presence of water. Locations containing clays and/or other hydrated minerals are promising places to search for evidence of life. Rock can form layers in a variety of ways. Volcanoes, wind, and water can produce layers. Layers can be hardened by the action of groundwater. Martian groundwater likely moved hundreds of kilometers, dissolving many minerals from the rock it passed through. When groundwater surfaces in low areas containing sediments, the thin Martian atmosphere causes water to evaporate, leaving behind minerals as deposits and/or cementing agents. Consequently, layers of dust are less likely to erode easily, as they become cemented together. On Earth, mineral-rich waters often evaporate, forming large deposits of salts and other minerals. Sometimes, water flows through Earth's aquifers and then evaporates at the surface, much like what is hypothesized for Mars. One location where this occurs on Earth is the Great Artesian Basin in Australia. On Earth, the hardness of many sedimentary rocks, such as sandstone, is largely due to the cement that forms as water passes through.
Schiaparelli Crater
Schiaparelli is a large impact crater on Mars, located near the planet's equator. It has a diameter of approximately 461 kilometers (286 mi) and is centered at a latitude of 3° south and a longitude of 344° east. Some regions within Schiaparelli display numerous layers that may have formed through aeolian (wind-driven) processes, volcanic activity, or sedimentary deposition in the presence of water.
Other craters When a comet or asteroid collides at high speed with the surface of Mars, it creates a primary impact crater. The impact can also eject a large number of rocks, which may fall back to the surface and form secondary craters. These secondary craters often appear in clusters. Because all the craters in such a cluster are subject to the same erosion patterns, they tend to appear similarly weathered, indicating that they are likely of the same age. If the secondary craters originated from a single, large, nearby impact, they would have formed nearly simultaneously. The image below of Denning Crater shows an example of a cluster of secondary craters. Impact craters generally have a raised rim and surrounding ejecta deposits, whereas volcanic craters typically lack both features. As impact craters increase in size—typically those greater than 10 km in diameter—they often develop a central peak. This peak results from the rebound of the crater floor immediately after the impact. By measuring the diameter of a crater, scientists can estimate its original depth using empirical ratios. This relationship has helped researchers determine that many Martian craters are partially filled with material—much of which is believed to be ice deposited during earlier climatic periods. Craters also often expose subsurface geological layers that were previously buried. During an impact, material from deep underground is ejected onto the surface, allowing scientists to study what lies beneath the Martian crust.
White rock in Pollack crater
Within this region lies Pollack Crater, which contains light-toned rock deposits. Mars has a significantly older surface compared to Earth. While much of Earth's surface is only a few hundred million years old due to active geological processes, large portions of the Martian surface are more than a billion years old. Some areas on Mars have undergone multiple cycles of deposition, erosion, and burial beneath newer layers. In the 1970s, the Mariner 9 spacecraft photographed a striking feature within a crater, which was named "White Rock." Initially, it was thought to be a salt deposit due to its light color. However, more recent data from instruments on the Mars Global Surveyor suggest that the material is likely volcanic ash or fine dust rather than salt. Later analysis revealed that "White Rock" only appears exceptionally bright because the surrounding terrain is unusually dark—giving the illusion of high contrast. Today, scientists believe that White Rock represents a remnant of a much larger sedimentary deposit that once filled the entire crater. Over time, much of it was eroded away, leaving only a fragment of the original formation. The image shows a detached outcrop of the same light-toned material some distance from the main deposit, supporting the idea that the white material once covered a significantly larger area.
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