The Margaritifer Sinus quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Margaritifer Sinus quadrangle is also referred to as MC-19 (Mars Chart-19).Davies, M.E.; Batson, R.M.; Wu, S.S.C. "Geodesy and Cartography" in Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W.; Matthews, M.S., Eds. Mars. University of Arizona Press: Tucson, 1992. The Margaritifer Sinus quadrangle covers the area from 0° to 45° west longitude and 0° to 30° south latitude on Mars. Margaritifer Sinus quadrangle contains Margaritifer Terra and parts of Xanthe Terra, Noachis Terra, Arabia Terra, and Meridiani Planum.

The name of this quadrangle means "pearl bay" after the pearl coast at Cape Comorin in South India.Blunck, J. 1982. Mars and its Satellites. Exposition Press. Smithtown, N.Y.

This quadrangle shows many signs of past water with evidence of lakes, deltas, ancient rivers, inverted channels, and chaos regions that released water.Grotzinger, J. and R. Milliken (eds.) 2012. Sedimentary Geology of Mars. SEPM Margaritifer Sinus contains some of the longest lake-chain systems on Mars, perhaps because of a wetter climate, more groundwater, or some of each factor. The Samara/Himera lake-chain system is about 1800 km long; the Parara/Loire valley network and lake-chain system is about 1100 km long.Fassett, C. and J. Head III. 2008. Valley network-fed, open-basin lakes on Mars: Distribution and implications for Noachian surface and subsurface hydrology. Icarus: 198. 39-56. A low area between Parana Valles and Loire Vallis is believed to have once held a lake.Goldspiel, J. and S. Squyres. 2000. Groundwater sapping and valley formation on Mars. Icarus. 89: 176-192. The 154 km diameter Holden Crater also once held a lake.Cabrol, N. and E. Grin (eds.). 2010. Lakes on Mars. Elsevier. NY. Near Holden Crater is a graben, called Erythraea Fossa, that once held a chain of three lakes.Buhler, P. et al. 2011. Evidence for palelakes in Erythracea Fossa, Mars: Implications for an ancient hydrological cycle. Icarus. 213: 104–115.

This region contains abundant clay-bearing sediments of Noachian age. Spectral studies with CRISM showed Fe/Mg-phyllosilicates, a type of clay. Biological materials can be preserved in clay. It is believed that this clay was formed in near-neutral pH water. The clay was not mixed with sulfates which form under acid conditions. Life is probably more likely to form under neutral pH conditions.Thomas, R., et al. 2017. EXTENSIVE EXPOSURE OF CLAY-BEARING NOACHIAN TERRAIN IN MARGARITIFER TERRA, MARS. Lunar and Planetary Science XLVIII (2017.). 1180.pdf

This region of Mars is famous because the Opportunity Rover landed there on January 25, 2004, at 1.94°S and 354.47°E (5.53° W). NASA declared the mission over in a press conference on February 13, 2019. This mission lasted almost 15 years. Russia's Mars 6 crash-landed in Margaritifer Sinus quadrangle at 23.9 S and 19.42 W.

Rock and mineral discoveries at Meridiani Planum

Opportunity Rover found that the soil at Meridiani Planum was very similar to the soil at Gusev crater and Ares Vallis; however in many places at Meridiani the soil was covered with round, hard, gray spherules that were named "blueberries".Yen, A., et al. 2005. An integrated view of the chemistry and mineralogy of martian soils. Nature. 435.: 49-54. These blueberries were found to be composed almost entirely of the mineral hematite. It was decided that the spectra signal spotted from orbit by Mars Odyssey was produced by these spherules. After further study it was decided that the blueberries were concretions formed in the ground by water.Bell, J (ed.) The Martian Surface. 2008. Cambridge University Press. Over time, these concretions weathered from what was overlying rock, and then became concentrated on the surface as a lag deposit. The concentration of spherules in bedrock could have produced the observed blueberry covering from the weathering of as little as one meter of rock.Squyres, S. et al. 2004. The Opportunity Rover's Athena Science Investigation at Meridiani Planum, Mars. Science: 1698-1703.Soderblom, L., et al. 2004. Soils of Eagle Crater and Meridiani Planum at the Opportunity Rover Landing Site. Science: 306. 1723-1726. Most of the soil consisted of olivine basalt sands that did not come from the local rocks. The sand may have been transported from somewhere else.Christensen, P., et al. Mineralogy at Meridiani Planum from the Mini-TES Experiment on the Opportunity Rover. Science: 306. 1733–1739.

Minerals in dust A Mössbauer spectrum was made of the dust that gathered on Opportunity's capture magnet. The results suggested that the magnetic component of the dust was titanomagnetite, rather than just plain magnetite, as was once thought. A small amount of olivine was also detected which was interpreted as indicating a long arid period on the planet. On the other hand, a small amount of hematite that was present meant that there may have been liquid water for a short time in the early history of the planet.Goetz, W., et al. 2005. Indication of drier periods on Mars from the chemistry and mineralogy of atmospheric dust. Nature: 436.62-65. Because the Rock Abrasion Tool (RAT) found it easy to grind into the bedrocks, it is thought that the rocks are much softer than the rocks at Gusev crater.

Bedrock minerals Few rocks were visible on the surface where Opportunity landed, but bedrock that was exposed in craters was examined by the suit of instruments on the Rover.Bell, J., et al. 2004. Pancam Multispectral Imaging Results from the Opportunity Rover at Meridiani Planum. Science: 306.1703-1708. Bedrock rocks were found to be sedimentary rocks with a high concentration of sulfur in the form of calcium and magnesium sulfates. Some of the sulfates that may be present in bedrocks are kieserite, sulfate anhydrate, bassanite, hexahydrite, epsomite, and gypsum. Salts, such as halite, bischofite, antarcticite, bloedite, vanthoffite, or glauberite, may also be present.Christensen, P., et al. 2004 Mineralogy at Meridiani Planum from the Mini-TES Experiment on the Opportunity Rover. Science: 306. 1733-1739.Squyres, S. et al. 2004. In Situ Evidence for an Ancient Aqueous Environment at Meridian Planum, Mars. Science: 306. 1709-1714.

The rocks containing the sulfates had a light tone compared to isolated rocks and rocks examined by landers/rovers at other locations on Mars. The spectra of these light toned rocks, containing hydrated sulfates, were similar to spectra taken by the Thermal Emission Spectrometer on board the Mars Global Surveyor. The same spectrum is found over a large area, so it is believed that water once appeared over a wide region, not just in the area explored by Opportunity Rover.Hynek, B. 2004. Implications for hydrologic processes on Mars from extensive bedrock outcrops throughout Terra Meridiani. Nature: 431. 156-159.

The Alpha Particle X-ray Spectrometer (APXS) found rather high levels of phosphorus in the rocks. Similar high levels were found by other rovers at Ares Vallis and Gusev Crater, so it has been hypothesized that the mantle of Mars may be phosphorus-rich.Dreibus, G. and H. Wanke. 1987. Volatiles on Earth and Marsw: a comparison. Icarus. 71:225-240 The minerals in the rocks could have originated by acid weathering of basalt. Because the solubility of phosphorus is related to the solubility of uranium, thorium, and rare earth elements, they are all also expected to be enriched in rocks.Rieder, R., et al. 2004. Chemistry of Rocks and Soils at Meridiani Planum from the Alpha Particle X-ray Spectrometer. Science. 306. 1746-1749

When Opportunity Rover traveled to the rim of Endeavour crater, it soon found a white vein that was later identified as being pure gypsum. It was formed when water carrying gypsum in solution deposited the mineral in a crack in the rock. A picture of this vein, called "Homestake" formation, is shown below.

Evidence for water

Examination of Meridiani rocks found strong evidence for past water. The mineral called jarosite which only forms in water was found in all bedrocks. This discovery proved that water once existed in Meridiani PlanumKlingelhofer, G. et al. 2004. Jarosite and Hematite at Meridiani Planum from Opportunity's Mossbauer Spectrometer. Science: 306. 1740-1745. In addition, some rocks showed small laminations (layers) with shapes that are only made by gently flowing water.Herkenhoff, K., et al. 2004. Evidence from Opportunity's Microscopic Imager for Water on Meridian Planum. Science: 306. 1727-1730 The first such laminations were found in a rock called "The Dells". Geologists would say that the cross-stratification showed festoon geometry from transport in subaqueous ripples. A picture of cross-stratification, also called cross-bedding, is shown on the left.

Box-shaped holes in some rocks were caused by sulfates forming large crystals, and then when the crystals later dissolved, holes, called vugs, were left behind. The concentration of the element bromine in rocks was highly variable probably because it is very soluble. Water may have concentrated it in places before it evaporated. Another mechanism for concentrating highly soluble bromine compounds is frost deposition at night that would form very thin films of water that would concentrate bromine in certain spots.

Rock from impact One rock, "Bounce Rock", found sitting on the sandy plains was found to be ejecta from an impact crater. Its chemistry was different from the bedrocks. Containing mostly pyroxene and plagioclase and no olivine, it closely resembled a part, Lithology B, of the shergottite meteorite EETA 79001, a meteorite known to have come from Mars. Bounce rock received its name by being near an airbag bounce mark.

Meteorites Opportunity Rover found meteorites just sitting on the plains. The first one analyzed with Opportunity's instruments was called "Heatshield Rock", as it was found near where Opportunity's headshield landed. Examination with the Miniature Thermal Emission Spectrometer (Mini-TES), Mossbauer spectrometer, and APXS lead researchers to, classify it as an IAB meteorite. The APXS determined it was composed of 93% iron and 7% nickel. The cobble named "Fig Tree Barberton" is thought to be a stony or stony-iron meteorite (mesosiderite silicate),Squyres, S., et al. 2009. Exploration of Victoria Crater by the Mars Rover Opportunity. Science: 1058-1061.Schroder, C., et al. 2008. J. Geophys. Res.: 113. while "Allan Hills", and "Zhong Shan" may be iron meteorites.

Geological history Observations at the site have led scientists to believe that the area was flooded with water a number of times and was subjected to evaporation and desiccation. In the process sulfates were deposited. After sulfates cemented the sediments, hematite concretions grew by precipitation from groundwater. Some sulfates formed into large crystals which later dissolved to leave vugs. Several lines of evidence point toward an arid climate in the past billion years or so, but a climate supporting water, at least for a time, in the distant past.Clark, B. et al. Chemistry and mineralogy of outcrops at Meridiani Planum. Earth Planet. Sci. Lett. 240: 73-94.Salvatore, M., M. Kraft1, C. Edwards, P. Christensen. 2015. Geologic History of margaitifer Basin, Mars: Evidence for a Prolonged Yet Episodic Hydrologic System. 46th Lunar and Planetary Science Conference (2015) 1463.pdf

Vallis

Vallis (plural valles) is the Latin word for "valley". It is used in planetary geology for the naming of valley landform features on other planets.