Aeolis quadrangle

The Aeolis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Aeolis quadrangle is also referred to as MC-23 (Mars Chart-23).^[1]

The Aeolis quadrangle covers 180° to 225° W and 0° to 30° south on Mars. It is famous because the Spirit Rover landed there (14.5718° S and 175.4785° E) on January 4, 2004 and drove around the area in Gusev crater snapping photos and analyzing rocks.

An overall view of MER-A Spirit landing site (denoted with a star)

Apollo Hills panorama from the Spirit landing site

What Spirit Rover discovered about rocks and minerals on Mars

The rocks on the plains of Gusev are a type of basalt. They contain the minerals olivine, pyroxene, plagioclase, and magnetite, and they look like volcanic basalt as they are fine-grained with irregular holes (geologists would say they have vesicles and vugs).^[2][3] Much of the soil on the plains came from the breakdown of the local rocks. Fairly high levels of nickel were found in some soils; probably from meteorites.^[4] Analysis shows that the rocks have been slightly altered by tiny amounts of water. Outside coatings and cracks inside the rocks suggest water deposited minerals, maybe bromine compounds. All the rocks contain a fine coating of dust and one or more harder rinds of material. One type can be brushed off, while another needed to be ground off by the Rock Abrasion Tool (RAT).^[5]

There are a variety of rocks in the Columbia Hills (Mars), some of which have been altered by water, but not by very much water.

The dust in Gusev Crater is the same as dust all around the planet. All the dust was found to be magnetic. Moreover, Spirit found the magnetism was caused by the mineral magnetite, especially magnetite that contained the element titanium. One magnet was able to completely divert all dust hence all Martian dust is thought to be magnetic.^[6] The spectra of the dust was similar to spectra of bright, low thermal inertia regions like Tharsis and Arabia that have been detected by orbiting satellites. A thin layer of dust, maybe less than one millimeter thick covers all surfaces. Something in it contains a small amount of chemically bound water.^[7][8]

Plains

Adirondack
Above: An approximate true color view of Adirondack, taken by Spirit's pancam. Right:Digital camera image (from Spirit's Pancam) of Adirondack after a RAT grind (Spirit's rock grinding tool)
Coordinates	14°36′S 175°30′E / 14.6°S 175.5°E / -14.6; 175.5Coordinates: 14°36′S 175°30′E / 14.6°S 175.5°E / -14.6; 175.5
Type of feature	Rock
v t e

Observations of rocks on the plains show they contain the minerals pyroxene, olivine, plagioclase, and magnetite. These rocks can be classified in different ways. The amounts and types of minerals make the rocks primitive basalts—also called picritic basalts. The rocks are similar to ancient terrestrial rocks called basaltic komatiites. Rocks of the plains also resemble the basaltic shergottites, meteorites which came from Mars. One classification system compares the amount of alkali elements to the amount of silica on a graph; in this system, Gusev plains rocks lay near the junction of basalt, picrobasalt, and tephite. The Irvine-Barager classification calls them basalts.^[9] Plain’s rocks have been very slightly altered, probably by thin films of water because they are softer and contain veins of light colored material that may be bromine compounds, as well as coatings or rinds. It is thought that small amounts of water may have gotten into cracks inducing mineralization processes).^[10][11] Coatings on the rocks may have occurred when rocks were buried and interacted with thin films of water and dust. One sign that they were altered was that it was easier to grind these rocks compared to the same types of rocks found on Earth.

The first rock that Spirit studied was Adirondack. It turned out to be typical of the other rocks on the plains.

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  First color picture from Gusev crater. Rocks were found to be basalt. Everything was covered with a fine dust that Spirit determined was magnetic because of the mineral magnetite.

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  Cross-sectional drawing of a typical rock from the plains of Gusev crater. Most rocks contain a coating of dust and one or more harder coatings. Veins of water-deposited veins are visible, along with crystals of olvine. Veins may contain bromine salts.

Columbia Hills

Scientists found a variety of rock types in the Columbia Hills, and they placed them into six different categories. The six are: Clovis, Wishbone, Peace, Watchtower, Backstay, and Independence. They are named after a prominent rock in each group. Their chemical compositions, as measured by APXS, are significantly different from each other.^[12] Most importantly, all of the rocks in Columbia Hills show various degrees of alteration due to aqueous fluids.^[13] They are enriched in the elements phosphorus, sulfur, chlorine, and bromine—all of which can be carried around in water solutions. The Columbia Hills’ rocks contain basaltic glass, along with varying amounts of olivine and sulfates.^[14][15] The olivine abundance varies inversely with the amount of sulfates. This is exactly what is expected because water destroys olivine but helps to produce sulfates.

The Clovis group is especially interesting because the Mossbauer spectrometer(MB) detected goethite in it.^[16]. Goethite forms only in the presence of water, so its discovery is the first direct evidence of past water in the Columbia Hills's rocks. In addition, the MB spectra of rocks and outcrops displayed a strong decline in olivine presence,^[17] although the rocks probably once contained much olivine.^[18] Olivine is a marker for the lack of water because it easily decomposes in the presence of water. Sulfate was found, and it needs water to form. Wishstone contained a great deal of plagioclase, some olivine, and anhydrate (a sulfate). Peace rocks showed sulfur and strong evidence for bound water, so hydrated sulfates are suspected. Watchtower class rocks lack olivine consequently they may have been altered by water. The Independence class showed some signs of clay (perhaps montmorillonite a member of the smectite group). Clays require fairly long term exposure to water to form. One type of soil, called Paso Robles, from the Columbia Hills, may be an evaporate deposit because it contains large amounts of sulfur, phosphorus, calcium, and iron.^[19] Also, MB found that much of the iron in Paso Robles soil was of the oxidized, Fe⁺⁺⁺ form, which would happen if water had been present.^[20]

Towards the middle of the six year mission (a mission that was supposed to last only 90 days), large amounts of pure silica were found in the soil. The silica could have come from the interaction of soil with acid vapors produced by volcanic activity in the presence of water or from water in a hot spring environment.^[21]

After Spirit stopped working scientists studied old data from the Miniature Thermal Emission Spectrometer, or Mini-TES and confirmed the presence of large amounts of carbonate-rich rocks, which means that regions of the planet may have once harbored water. The carbonates were discovered in an outcrop of rocks called “Comanche.”^[22][23]

In summary, Spirit found evidence of slight weathering on the plains of Gusev, but no evidence that a lake was there. However, in the Columbia Hills there was clear evidence for a moderate amount of aqueous weathering. The evidence included sulfates and the minerals goethite and carbonates which only form in the presence of water. It is believed that Gusev crater may have held a lake long ago, but it has since been covered by igneous materials. All the dust contains a magnetic component which was identified as magnetite with some titanium. Furthermore the thin coating of dust that covers everything on Mars is the same in all parts of Mars.

Ma'adim Vallis

A large, ancient river valley, called Ma'adim Vallis, enters at the south rim of Gusev Crater, so Gusev Crater was believed to be an ancient lake bed. However, it seems that a volcanic flow covered up the lakebed sediments.^[24] Apollinaris Patera, a large volcano, lies directly north of Gusev Crater.^[25]

Recent studies lead scientists to believe that the water that formed Ma'adim Vallis originated in a complex of lakes. When the largest lake spilled over the low point in its boundary, a torrential flood would have moved north, carving the sinuous Ma'adim Vallis. At the north end of Ma'adim Vallis, the flood waters would have run into Gusev Crater.^[26]

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  Section of Ma'adim Vallis as seen by HiRISE. A more recent flow of water may have formed the smaller, deeper channel to the right.

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  Apollinaris Patera

Gale Crater

Gale Crater, in the northwestern part of the Aeolis quadrangle, is of special interest to geologists because it contains a 2–4 km (1.2-2.5 mile) high mound of layered sedimentary rocks. On 28 March 2012 this mound was officially named Mount Sharp by NASA in honor of Robert P. Sharp (1911-2004), a planetary scientist of early Mars missions.^[27][28][29] More recently, on 16 May 2012, Mount Sharp was renamed to Aeolis Mons by the USGS.^[30] The mound extends higher than the rim of the crater, so perhaps the layering covered an area much larger than the crater.^[31] These layers are a complex record of the past. The rock layers probably took millions of years to be laid down within the crater, then more time to be eroded to make them visible.^[32] There is evidence that the first phase of erosion was followed by more cratering and more rock formation.^[33]

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  Layers in Gale Crater as seen by HiRISE. Layers may have formed by deposition in a lake, or by deposition of windblown particles.

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  Gale Crater Grand Canyon, as seen by HiRISE. Scale bar is 500 meters long.

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  Gale Crater-Colorized composite of MOC wide angle and MGS laser altimeter data. Credit NASA/JPL.MSSS

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  The high mound in Gale crater was probably formed from erosion of layers that covered the whole area, as shown in here.

Other Craters

Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits. As craters get larger (greater than 10 km in diameter) they usually have a central peak.^[34] The peak is caused by a rebound of the crater floor following the impact.^[35] Sometimes craters will display layers. Since the collision that produces a crater is like a powerful explosion, rocks from deep underground are tossed unto the surface. Hence, craters can show us what lies deep under the surface.

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  Boeddicker Crater Floor, as seen by HiRISE.

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  Central uplift of an Unnamed crater on the floor of Molesworth Crater, as seen by HiRISE. Dark sand dunes are on left side of image. The scale bar is 500 meters long.

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  Reuyl Crater Central Peak, as seen by HiRISE.

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  Galdakao Crater,as seen by HiRISE. Click on image to see Dark Slope Streaks.

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  Layers in crater wall, as seen by HiRISE under HiWish program. Area in box is enlarged in the next image.

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  Enlargement from previous image, showing many thin layers. Note that the layers do not seem to be formed from rocks. They may be all that is left of a deposit that once filled the crater. Image was taken with HiRISE, under HiWish program.

Mars Science Laboratory

The aim of the Mars Science Laboratory is to search for signs of ancient life. It is hoped that a later mission could then return samples that the laboratory identified as probably containing remains of life. To safely bring the craft down, a 12 mile wide, smooth, flat circle is needed. Geologists hope to examine places where water once ponded.^[36] They would like to examine sediment layers. The Mars Science Laboratory is expected to land in Gale Crater on 6 August 2012.^{[27][28][29][37][38]}

Inverted Relief

Some places on Mars show inverted relief. In these locations, a stream bed may be a raised feature, instead of a valley. The inverted former stream channels may be caused by the deposition of large rocks or due to cementation. In either case erosion would erode the surrounding land but leave the old channel as a raised ridge because the ridge will be more resistant to erosion. An image below, taken with HiRISE shows sinuous ridges that may be old channels that have become inverted.^[39]

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  Meandering Ridges that are probably inverted stream channels. Image taken with HiRISE.

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  CTX image of craters with black box showing location of next image.

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  Image from previous photo of a curved ridge that may be an old stream that has become inverted. Image taken with HiRISE under the HiWish program.

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  Sinuous Ridges within a branching fan in lower member of Medusae Fossae Formation, as seen by HiRISE.

Yardangs

Yardangs are common on Mars. They are generally visible as a series of parallel linear ridges. Their parallel nature is thought to be caused by the direction of the prevailing wind. Two HiRISE images below show a good view of yardangs in the Aeolis quadrangle.^[39] Yardangs are common in the Medusae Fossae Formation on Mars.

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  Stream channels in inverted relief and yardangs, as seen by HiRISE.

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  Aeolis Mensae Yardangs, as seen by HiRISE. Scale bar is 500 meters long. Click on image for better view of yardangs.

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  Medusae Fossae Formation southeast of Apollinaris Patera, as seen by HiRISE.

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  Yardangs in Medusae Fossae Formation with caprock labeled, as seen by HiRISE.

Gallery

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  Layers in lower member of Medusae Fossae Formation, as seen by HiRISE.

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  Map of Aeolis quadrangle. The Spirit Rover landed in Gusev crater. It found volcanic rocks that probably came from Apollinaris Patera. A large pile of layered rocks sits in the middle of Gale Crater.

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  Buttes and layers in Aeolis, as seen by Mars Global Surveyor.

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  Layers along crater rim in Terra Sirenum, as seen by HiRIS under the HiWish program.

See also

• Climate of Mars
• Water on Mars
• Geology of Mars
• Impact crater
• Inverted relief
• Groundwater on Mars
• Composition of Mars
• Carbonates on Mars
• Martian soil
• Scientific information from the Mars Exploration Rover mission
• Columbia Hills (Mars)
• Adirondack (Mars)

References