Nili Fossae is a group of large, concentric grabens on Mars, in the Syrtis Major quadrangle. They have been eroded and partly filled in by

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

s and

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

-rich ejecta from a nearby giant

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

, the

Isidis basin Isidis Planitia is a plain located within a giant impact basin on Mars, located partly in the Syrtis Major quadrangle and partly in the Amenthes quadrangle. At approximately in diameter, it is the third-largest obvious impact structure on the ...

. It is at approximately 22°N, 75°E, and has an elevation of . Nili Fossae was on the list of potential landing sites of the

Mars Science Laboratory Mars Science Laboratory (MSL) is a robotic space probe mission to Mars launched by NASA on November 26, 2011, which successfully landed ''Curiosity'', a Mars rover, in Gale Crater on August 6, 2012. The overall objectives include investigati ...

, arriving in 2012, but was dropped before the final four sites were determined. Although not among the last finalists, in September 2015 it was selected as a potential landing site for the

Mars 2020 Mars 2020 is a Mars rover mission forming part of NASA's Mars Exploration Program that includes the rover '' Perseverance'', the small robotic, coaxial helicopter '' Ingenuity'', and associated delivery vehicles. Mars 2020 was launched from ...

rover, which will use the same design as ''

Curiosity Curiosity (from Latin '' cūriōsitās'', from ''cūriōsus'' "careful, diligent, curious", akin to ''cura'' "care") is a quality related to inquisitive thinking such as exploration, investigation, and learning, evident by observation in humans ...

'', but with a different payload focused on astrobiology. A large exposure of

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

is in Nili Fossae. In December 2008,

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

Mars Reconnaissance Orbiter ''Mars Reconnaissance Orbiter'' (MRO) is a spacecraft designed to study the geology and climate of Mars, provide reconnaissance of future landing sites, and relay data from surface missions back to Earth. It was launched on August 12, 2005, an ...

found that rocks at Nili Fossae contain

carbonate minerals Carbonate minerals are those minerals containing the carbonate ion, . Carbonate divisions Anhydrous carbonates *Calcite group: trigonal **Calcite CaCO3 **Gaspéite (Ni,Mg,Fe2+)CO3 **Magnesite MgCO3 **Otavite CdCO3 **Rhodochrosite MnCO3 **Sider ...

, a geologically significant discovery. Other minerals found by MRO are aluminum

smectite A smectite (from ancient Greek ''σμηκτός'' smektos 'lubricated'; ''σμηκτρίς'' smektris 'walker's earth', 'fuller's earth'; rubbing earth; earth that has the property of cleaning) is a mineral mixtures of various swelling sheet sil ...

, iron/

magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

smecite, hydrated

silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is ...

, kaolinite group minerals, and iron oxides. NASA scientists discovered that Nili Fossae is the source of plumes of

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane on Ea ...

, raising the question of whether this source originates from biological sources. Researchers in July 2010 suggested that carbonate bearing rocks found in the Nili Fossae region of Mars are made up of hydrothermally altered

ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...

rocks. Consequently, hydrothermal activity would have provided sufficient energy for biological activity. Evidence of living organisms could have been preserved. Nili Fossae trough is thought to have resulted from the impact that formed the nearby Isidis basin. Nili Fossae Trough was one of seven finalists for the MSL landing site: * Eberswalde Crater *

Gale Crater Gale is a crater, and probable dry lake, at in the northwestern part of the Aeolis quadrangle on Mars. It is in diameter and estimated to be about 3.5–3.8 billion years old. The crater was named after Walter Frederick Gale, an amateur ast ...

* Holden Crater *

Mawrth Vallis Mawrth Vallis () (Mawrth means "Mars" in Welsh) is a valley on Mars, located in the Oxia Palus quadrangle at 22.3°N, 343.5°E with an elevation approximately two kilometers below datum. Situated between the southern highlands and northern lowlan ...

* Miyamoto Crater *Nili Fossae Trough *Southern Meridiani

References

{{Authority control Valleys and canyons on Mars Mars 2020 Syrtis Major quadrangle