Mount Sharp rises from the middle of the crater - thegreen dot marksBradbury Landing, theCuriosity rover landing site inAeolis Palus (click the image to expand, the dot is barely visible at this scale.) North is down in this image.
Colorized shaded relief map of the crater Gale. The general landing area forCuriosity on the northwestern crater floor, namedAeolis Palus, is circled. (HRSC data)
Gale, named forWalter F. Gale (1865–1945), an amateur astronomer from Australia, spans 154 km (96 mi) in diameter and holds a mountain, Aeolis Mons (informally named "Mount Sharp" to pay tribute to geologistRobert P. Sharp) rising 18,000 ft (5,500 m) from the crater floor, higher thanMount Rainier rises above Seattle. Gale is roughly the size of Connecticut and Rhode Island.
The crater formed when anasteroid orcomet hit Mars in its early history, about 3.5 to 3.8 billion years ago. Theimpactor punched a hole in the terrain, and the subsequent explosion ejected rocks and soil that landed around the crater. Layering in the central mound (Aeolis Mons) suggests it is the surviving remnant of an extensive sequence of deposits. Some scientists believe the crater filled in with sediments and, over time, the relentless Martian winds carved Aeolis Mons, which today rises about 5.5 km (3.4 mi) above the floor of Gale—three times higher than the Grand Canyon is deep.[18]
At 10:32 p.m. PDT on August 5, 2012 (1:32 a.m. EDT on August 6, 2012), the Mars Science Laboratory roverCuriosity landed on Mars at4°30′S137°24′E / 4.5°S 137.4°E /-4.5; 137.4, at the foot of the layered mountain inside Gale.Curiosity landed within a landing ellipse approximately 7 km (4.3 mi) by 20 km (12 mi). The landing ellipse is about 4,400 m (14,400 ft) below Martian "sea level" (defined as the average elevation around the equator). The expected near-surface atmospheric temperatures at the landing site duringCuriosity's primary mission (1 Martian year or 687 Earth days) are from −90 to 0 °C (−130 to 32 °F).
Scientists chose Gale as the landing site forCuriosity because it has many signs that water was present over its history. The crater's geology is notable for containing both clays and sulfate minerals, which form in water under different conditions and may also preserve signs of past life. The history of water at Gale, as recorded in its rocks, is givingCuriosity many clues to study as it pieces together whether Mars ever could have been a habitat for microbes. Gale contains a number of fans and deltas that provide information about lake levels in the past, including: Pancake Delta, Western Delta, Farah Vallis delta and the Peace Vallis Fan.[19]
OrbitalTHEMIS and topography data, plus visible andnear-infrared images, were used to make ageological map of the crater.CRISM data indicated the lowerbench unit was composed of interstratifiedclay andsulfates. Curiosity explored the stratigraphy of the crater consisting of the BradburyGroup and the overlying Mount Sharp Group.Formations within the Bradbury Group include the Yellowknife and Kimberley, while the Murray Formation is at the base of the Mount Sharp Group. The Bradbury Group consists offluvialconglomerates,cross-beddedsandstones, andmudstones reflecting abasalticprovenance. Sandstone clinoforms indicatedeltaic deposits. The Murray Formation is a laminated mudstone overlain by a cross-bedded or clinoform sandstone, though in places the base is a conglomerate. Thus, the formation is interpreted to have been deposited in alacustrine environment adjacent to a fluvial-deltaic one. The Murray Formation is overlain by clay and sulfate-bearing strata.[20]
An unusual feature of Gale is an enormous mound of "sedimentary debris"[21] around its central peak, officially namedAeolis Mons[5][6] (popularly known as "Mount Sharp"[22][23]) rising 5.5 km (18,000 ft) above the northern crater floor and 4.5 km (15,000 ft) above the southern crater floor—slightly taller than the southern rim of the crater itself. The mound is composed of layered material and may have been laid down over a period of around 2 billion years.[3] The origin of this mound is not known with certainty, but research suggests it is the eroded remnant of sedimentary layers that once filled the crater completely, possibly originally deposited on a lakebed.[3] Evidence of fluvial activity was observed early on in the mission at the Shaler outcrop (first observed on Sol 120, investigated extensively between Sols 309-324).[24] Observations made by the roverCuriosity at the Pahrump Hills strongly support the lake hypothesis: sedimentaryfacies including sub mm-scale horizontally-laminated mudstones, with interbedded fluvialcrossbeds are representative of sediments which accumulate in lakes, or on the margins of lakes which grow and contract in response to lake-level.[25][26] These lake-bed mudstones are referred to as theMurray Formation, and form a significant amount of the Mount Sharp group. The Siccar Point group (named after the famous unconformity atSiccar Point) overlies the Mount Sharp group,[27] and the two units are separated by a majorunconformity which dips toward the North.[28] At present, the Stimson formation is the only stratigraphic unit within the Siccar Point group which has been investigated in-detail byCuriosity. The Stimson formation represents the preserved expression of a dryaeoliandune field, where sediment was transported towards the north, or northeast by palaeowinds within the crater.[29][30] In the Emerson plateau area (from Marias Pass, to East Glacier), the outcrops are characterised predominantly by simple cross-sets, deposited by simple sinuous-crested dunes, with heights up to ~10 m.[29] To the south, at the Murray buttes, the outcrop are characterised by compound cross-sets, with a hierarchy of bounding surfaces migration of small dunes superimposed on the lee-slope of a large dune known as a "draa".[30] Thesedraas have estimates heights of ~40 m, and migrated toward the north, while superimposed dunes migrated toward the east-northeast.[30] Further to the south, at the Greenheugh pediment, compound and simple cross-sets consistent with aeolian depositional processes have been observed in the pediment capping unit.[31] Observations made during the ascent of the Greenheugh pediment between Sols 2665-2734 demonstrated that the pediment capping unit has sedimentary textures, facies and architecture that are consistent with the rest of the Stimson formation.[32] Furthermore, analysis of sedimentary facies and architecture provided evidence which indicates fluctuating wind directions, from a seasonal temporal scale - recorded by interstratified windripple and avalanche strata, through to millennial time scales recorded by reversal of the sediment transport direction.[33] These wind reversals suggest variable and changeable atmospheric circulation during this time.
Observations of possible cross-bedded strata on the upper mound suggestaeolian processes, but the origin of the lower mound layers remains ambiguous.[34]
In February 2019, NASA scientistsreported that theMarsCuriosity rover had determined, for the first time, thedensity ofMount Sharp in Gale, thereby establishing a clearer understanding of how the mountain was formed.[35][36]
Curiosity's view of the interior of Gale from the slopes (at 327 m (1,073 ft) elevation) ofMount Sharp (video (1:53)) (October 25, 2017)
Numerous channels eroded into the flanks of the crater's central mound could give access to the layers for study.[3] Gale is the landing site of theCuriosity rover, delivered by theMars Science Laboratory spacecraft,[38] which was launched November 26, 2011 and landed on Mars inside the crater Gale on the plains ofAeolis Palus[39] on August 6, 2012.[40][41][42][43] Gale was previously a candidate landing site for the 2003Mars Exploration Rover mission, and has been one of four prospective sites forESA'sExoMars.[44]
On September 26, 2013, NASA scientists reported thatCuriosity detected "abundant, easily accessible"water (1.5 to 3 weight percent) insoil samples at theRocknest region ofAeolis Palus in Gale.[48][49][50][51][52][53] In addition, the rover found two principal soil types: a fine-grainedmafic type and a locally derived, coarse-grainedfelsic type.[50][52][54] The mafic type, similar to othermartian soils andmartian dust, was associated with hydration of the amorphous phases of the soil.[54] Also,perchlorates, the presence of which may make detection of life-relatedorganic molecules difficult, were found at theCuriosity landing site (and earlier at the more polar site of thePhoenix lander) suggesting a "global distribution of these salts".[53] NASA also reported thatJake M rock, a rock encountered byCuriosity on the way toGlenelg, was amugearite and very similar to terrestrial mugearite rocks.[55]
On December 9, 2013, NASA reported that, based on evidence fromCuriosity studying Aeolis Palus, Gale contained an ancientfreshwater lake which could have been a hospitable environment formicrobial life.[56][57]
On December 16, 2014, NASA reported detecting, by theCuriosity rover at Gale, an unusual increase, then decrease, in the amounts ofmethane in theatmosphere of the planetMars; in addition,organic chemicals were detected in powder drilled from arock. Also, based ondeuterium tohydrogen ratio studies, much of thewater at Gale on Mars was found to have been lost during ancient times, before the lakebed in the crater was formed; afterwards, large amounts of water continued to be lost.[58][59][60]
On October 8, 2015, NASA confirmed that lakes and streams existed in Gale 3.3 to 3.8 billion years ago delivering sediments to build up the lower layers ofMount Sharp.[61][62]
On June 1, 2017, NASA reported that theCuriosity rover provided evidence of an ancient lake in Gale onMars that could have been favorable formicrobial life; the ancient lake wasstratified, with shallows rich inoxidants and depths poor in oxidants; and, the ancient lake provided many different types of microbe-friendly environments at the same time. NASA further reported that theCuriosity rover will continue to explore higher and younger layers ofMount Sharp in order to determine how the lake environment in ancient times on Mars became the drier environment in more modern times.[63][64][65]
On June 7, 2018,NASA'sCuriosity made two significant discoveries in Gale.Organic molecules preserved in 3.5 billion-year-old bedrock and seasonal variations in the level ofmethane in the atmosphere further support the theory that past conditions may have been conducive to life.[68][69][70][71][72][73][74][75] It is possible that a form of water-rock chemistry might have generated the methane, but scientists cannot rule out the possibility of biological origins. Methane previously had been detected in Mars's atmosphere in large, unpredictable plumes. This new result shows that low levels of methane within Gale repeatedly peak in warm, summer months and drop in the winter every year. Organic carbon concentrations were discovered on the order of 10 parts per million or more. This is close to the amount observed in Martian meteorites and about 100 times greater than prior analysis of organic carbon on Mars's surface. Some of the molecules identified include thiophenes, benzene, toluene, and small carbon chains, such as propane or butene.[68]
On November 4, 2018, geologists presented evidence, based on studies in Gale by theCuriosity rover, that there was plenty ofwater on earlyMars.[76][77] In January 2020, researchers have found certain minerals, made of carbon and oxygen, in rocks at Gale, which may have formed in an ice-covered lake during a cold stage between warmer periods, or after Mars lost most of its atmosphere and became permanently cold.[78]
On November 5, 2020, researchers concluded based on data observed byCuriosity rover that Gale experienced megafloods which occurred around 4 billion years ago, taking into considerationantidunes reaching the height of 10 meters (33 ft), which were formed by flood waters at least 24 meters (79 ft) deep with a velocity of 10 meters per second (22 mph).[79]
Research published in August, 2023 found evidence that liquid water may have existed over thousands to millions of years and not just when an impact or volcano erupted. Shapes in a field of hexagonal ridges revealed that water appeared and then went away many times. The water did not just result from ground ice melting from something like an asteroid impact. To make these ridges many cycles of water saturating the surface and then drying were required. Chemicals were deposited by mineral-rich fluids in cracks. The minerals hardened such that they were harder than the rock around them. Later, when erosion took place, ridges were exposed.
Mudcracks as seen byCuriosity in Gale. Shapes imply that water saturated the area and dried out many times; hence, the existence of water was not just a one-time, short-lived event.
This discovery is significant. Much evidence exists to show that impacts and volcanic activity could melt ground ice to make liquid water. However, that water may not last long enough for life to develop. This new finding shows here it is not the case–water stayed for some time. Also, with water coming and going on a regular pace, there is a better chance of more complex organic compounds being produced. As water evaporates chemicals are concentrated and have a better chance of combining. For example when amino acids are concentrated they are more likely to link up to form proteins.[80][81]
Curiosity found features that computer simulations show could be caused by past streams. They have been called benches and noses. The "noses" stick out like noses. Computer simulations show that these shapes can be produced by rivers.[82][83]
In July 2024 the Rover cracked open a rock with its wheel and found crystals ofsulfur. Minerals containing sulfur were discovered, but never the pure element. It was found in Gediz Vallis.[84]
Research published in February 2025 described wave ripples in Gale that show that liquid water flowed there. The ripples were found in two different time periods. Calculations based on their shape and sizes revealed that they were formed in shallow moving water. The water could have been as deep as 2 meters. Before this study, it was thought that any exposed body of water would quickly develop a sheet of ice at the top.[85][86]
Curiosity's view of the "Rocknest" area - south is center/north at both ends; Mount Sharp at SE horizon (somewhat left-of-center); "Glenelg" at east (left-of-center); rover tracks at west (right-of-center) (November 16, 2012;white balanced) (raw color) (interactives)
^Dietrich, W. E.; Palucis, M. C.; Parker, T.; Rubin, D.; Lewis, K.; Sumner, D.; Williams, R.M.E. (2014).Clues to the relative timing of lakes in Gale Crater(PDF) (Report). Eighth International Conference on Mars (2014).
^Does the Greenheugh pediment capping unit represent a coninuation of the Stimson formation? S.G. Banham, S. Gupta, A.B. Bryk, D.M. Rubin, K.S. Edgett, W.E. Dietrich, C.M. Fedo, L.A. Edgar and A.R Vasavada, 51st Lunar and Planetary Science Conference (2020)https://www.hou.usra.edu/meetings/lpsc2020/pdf/2337.pdf
^Anderson, Ryan B.; Bell, James F. III (2010). "Geologic mapping and characterization of Gale Crater and implications for its potential as a Mars Science Laboratory landing site".The Mars Journal.5:76–128.Bibcode:2010IJMSE...5...76A.doi:10.1555/mars.2010.0004.S2CID3505206.
^H. B. Franz; et al. (2020). "Indigenous and exogenous organics and surface–atmosphere cycling inferred from carbon and oxygen isotopes at Gale crater". Vol. 4. Nature Astronomy. pp. 526–532.doi:10.1038/s41550-019-0990-x.
^E. Heydari; et al. (2020). "Deposits from giant floods in Gale crater and their implications for the climate of early Mars". Vol. 10, no. 19099. Scientific Reports.doi:10.1038/s41598-020-75665-7.
^Rapin, W., et al. 2023. Sustained wet–dry cycling on early Mars.Nature. Vol 620: 299
^Cardenas, B., and K. Staciey. 2023. Landforms Associated With the Aspect-Controlled Exhumation of Crater-Filling Alluvial Strata on Mars. Geophysical Research letters. Volume50, Issue15 16 August 2023 e2023GL103618
^Mondro, C., et al. 2015. Wave ripples formed in ancient, ice-free lakes in Gale crater, Mars. Science Advances. Vol 11, Issue 3. DOI: 10.1126/sciadv.adr0010
![Estimated size of ancient lake on Aeolis Palus in Gale[56][57]](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aPIA17596-MarsCuriosityRover-AncientLake-20131209.jpg)
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