The geological units on the floor of Jezero crater, Mars, are part of a wider regional stratigraphy of olivine-rich rocks, which extends well beyond the crater. We investigate the petrology of ...olivine and carbonate-bearing rocks of the Séítah formation in the floor of Jezero. Using multispectral images and x-ray fluorescence data, acquired by the Perseverance rover, we performed a petrographic analysis of the Bastide and Brac outcrops within this unit. We find that these outcrops are composed of igneous rock, moderately altered by aqueous fluid. The igneous rocks are mainly made of coarse-grained olivine, similar to some Martian meteorites. We interpret them as an olivine cumulate, formed by settling and enrichment of olivine through multi-stage cooling of a thick magma body.
Carbonate minerals have been detected in Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, and within the regional olivine‐bearing (ROB) unit in the ...Nili Fossae region surrounding this crater. It has been suggested that some carbonates in the margin fractured unit, a rock unit within Jezero crater, formed in a fluviolacustrine environment, which would be conducive to preservation of biosignatures from paleolake‐inhabiting lifeforms. Here, we show that carbonate‐bearing rocks within and outside of Jezero crater have the same range of visible‐to‐near‐infrared carbonate absorption strengths, carbonate absorption band positions, thermal inertias, and morphologies. Thicknesses of exposed carbonate‐bearing rock cross‐sections in Jezero crater are ∼75–90 m thicker than typical ROB unit cross‐sections in the Nili Fossae region, but have similar thicknesses to ROB unit exposures in Libya Montes. These similarities in carbonate properties within and outside of Jezero crater is consistent with a shared origin for all of the carbonates in the Nili Fossae region. Carbonate absorption minima positions indicate that both Mg‐ and more Fe‐rich carbonates are present in the Nili Fossae region, consistent with the expected products of olivine carbonation. These estimated carbonate chemistries are similar to those in martian meteorites and the Comanche carbonates investigated by the Spirit rover in Columbia Hills. Our results indicate that hydrothermal alteration is the most likely formation mechanism for non‐deltaic carbonates within and outside of Jezero crater.
Plain Language Summary
Spacecraft orbiting Mars can measure the composition of rocks that make up its surface. Understanding rock composition allows us to interpret past environmental conditions on Mars, including their likelihood to be habitable. Using data acquired from orbit, researchers have found carbonate minerals in Jezero crater and the surrounding region—called the Nili Fossae region. Jezero crater is the landing site of NASA's Mars 2020 Perseverance rover and once contained a lake. The discovery of carbonates is exciting because on Earth they sometimes form in habitable environments and preserve fossils. In this study, we used all available high resolution orbital datasets to look at similarities and differences between carbonate‐bearing rocks within and outside of Jezero crater. We found that carbonate‐bearing rocks within and outside of Jezero crater have similar orbital properties, implying that they formed by the same processes. We found that the range in chemistries (magnesium‐rich vs. iron‐rich) for carbonates within and outside of Jezero crater is similar to carbonate chemistries found in martian meteorites and by other rovers on Mars. The carbonates within and outside of Jezero crater could have formed by the same water‐rock interactions that formed carbonates discovered in martian meteorites and by other rovers on Mars.
Key Points
Carbonates within and outside of Jezero crater have similar spectra, thermal inertias, morphologies, and thicknesses
Carbonates within and outside of Jezero crater likely formed via the same processes
Hydrothermal alteration and evaporation are the most likely processes for carbonate formation within and outside of Jezero crater
This paper provides an overview of the Curiosity rover's exploration at Vera Rubin ridge (VRR) and summarizes the science results. VRR is a distinct geomorphic feature on lower Aeolis Mons ...(informally known as Mount Sharp) that was identified in orbital data based on its distinct texture, topographic expression, and association with a hematite spectral signature. Curiosity conducted extensive remote sensing observations, acquired data on dozens of contact science targets, and drilled three outcrop samples from the ridge, as well as one outcrop sample immediately below the ridge. Our observations indicate that strata composing VRR were deposited in a predominantly lacustrine setting and are part of the Murray formation. The rocks within the ridge are chemically in family with underlying Murray formation strata. Red hematite is dispersed throughout much of the VRR bedrock, and this is the source of the orbital spectral detection. Gray hematite is also present in isolated, gray‐colored patches concentrated toward the upper elevations of VRR, and these gray patches also contain small, dark Fe‐rich nodules. We propose that VRR formed when diagenetic event(s) preferentially hardened rocks, which were subsequently eroded into a ridge by wind. Diagenesis also led to enhanced crystallization and/or cementation that deepened the ferric‐related spectral absorptions on the ridge, which helped make them readily distinguishable from orbit. Results add to existing evidence of protracted aqueous environments at Gale crater and give new insight into how diagenesis shaped Mars' rock record.
Plain Language Summary
Vera Rubin ridge is a feature at the base of Mount Sharp with a distinct texture and topography. Orbiter observations showed hematite, a mineral that sometimes forms by chemical reactions in water environments, was present atop the ridge. The presence of both water and chemical activity suggested the area preserved a past habitable environment. In this paper, we detail how the Curiosity science team tested this and other orbital‐based hypotheses. Curiosity data suggested that most ridge rocks were lain down in an ancient lake and had similar compositions to other Mount Sharp rocks. Curiosity confirmed that hematite was present in the ridge but no more abundantly than elsewhere. Larger grain size or higher crystallinity probably account for the ridge's hematite being more visible from orbit. We conclude Vera Rubin ridge formed because groundwater recrystallized and hardened the rocks that now make up the ridge. Wind subsequently sculpted and eroded Mount Sharp, leaving the harder ridge rocks standing because they resisted erosion compared with surrounding rocks. The implication of these results is that liquid water was present at Mount Sharp for a very long time, not only when the crater held a lake but also much later, likely as groundwater.
Key Points
We summarize Curiosity's campaign at Vera Rubin ridge (Sols 1726–2302) and the high‐level results from articles in this special issue
Vera Rubin ridge formed when diagenesis hardened rocks along the base of Aeolis Mons; wind subsequently etched the feature into a ridge
Results add evidence for protracted aqueous environments at Gale crater and give new insight into how diagenesis shaped Mars' rock record
The surface of Mars exhibits strong evidence for a widespread and long‐lived cryosphere. Observations of the surface have identified phases produced by water‐rock interactions, but the contribution ...of glaciers to the observed alteration mineralogy is unclear. To characterize the chemical alteration expected on an icy early Mars, we collected water and rock samples from terrestrial glaciated volcanics. We related geochemical measurements of meltwater to the mineralogy and chemistry of proglacial rock coatings. In these terrains, water is dominated by dissolved silica relative to other dissolved cations, particularly at mafic sites. Rock coatings associated with glacial striations on mafic boulders include a silica‐rich component, indicating that silica precipitation is occurring in the subglacial environment. We propose that glacial alteration of volcanic bedrock is dominated by a combination of high rates of silica dissolution and precipitation of opaline silica. On Mars, cryosphere‐driven chemical weathering could be the origin of observed silica‐enriched phases.
Plain Language Summary
The planet Mars has glaciers and ice sheets on its surface and probably did in the past. Minerals on the planet's surface form in the presence of water, but it is unclear which minerals may have formed due to liquid water under warm climates versus those formed under much colder climates. In order to study this problem, we collected rocks and water from Mars‐like analog sites: glaciated volcanoes. We measured the chemistry of the water and the mineralogy and chemistry of rock coatings found near the glaciers. Both the water and the rock coatings were high in silica. We propose that glaciers alter volcanic bedrock by dissolving and precipitating noncrystalline silica. Silica detected on the surface of Mars could have formed due to similar processes.
Key Points
Chemical alteration of glaciated volcanic bedrock is dominated by silica dissolution and precipitation
Dissolved silica in glacial meltwater is greater at more mafic study sites and results in deposition of opaline silica rock coatings
Past glacial chemical weathering may be responsible for some amorphous silica deposits on the highly mafic surface of Mars
Visible/short‐wave infrared spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions attributed to hematite at Vera Rubin ridge (VRR), a topographic ...feature on northwest Mt. Sharp. The goals of this study are to determine why absorptions caused by ferric iron are strongly visible from orbit at VRR and to improve interpretation of CRISM data throughout lower Mt. Sharp. These goals are achieved by analyzing coordinated CRISM and in situ spectral data along the Curiosity Mars rover's traverse. VRR bedrock within areas that have the deepest ferric absorptions in CRISM data also has the deepest ferric absorptions measured in situ. This suggests strong ferric absorptions are visible from orbit at VRR because of the unique spectral properties of VRR bedrock. Dust and mixing with basaltic sand additionally inhibit the ability to measure ferric absorptions in bedrock stratigraphically below VRR from orbit. There are two implications of these findings: (1) Ferric absorptions in CRISM data initially dismissed as noise could be real, and ferric phases are more widespread in lower Mt. Sharp than previously reported. (2) Patches with the deepest ferric absorptions in CRISM data are, like VRR, reflective of deeper absorptions in the bedrock. One model to explain this spectral variability is late‐stage diagenetic fluids that changed the grain size of ferric phases, deepening absorptions. Curiosity's experience highlights the strengths of using CRISM data for spectral absorptions and associated mineral detections and the caveats in using these data for geologic interpretations and strategic path planning tools.
Plain Language Summary
Satellites orbiting Mars map the composition of the planet's surface, tell us about past environments, and guide rovers to interesting locations on the surface. The Curiosity rover investigated a ridge named Vera Rubin ridge where indications of the mineral hematite (Fe2O3) was suggested from orbital data. In this paper, we investigate why the hematite detection on the ridge was so clear from orbit and what the implications are for how the hematite formed. We found several factors influence the orbital data, but the biggest reason hematite at Vera Rubin ridge was so easily detected from orbit was because the bedrock there was unique. Water had interacted with rocks at the ridge sometime after they were deposited, and this interaction affected the properties of the hematite and made it more visible from orbit. Curiosity's data help us reinterpret the orbital data over Mt. Sharp and reveal hematite is probably present in most of the bedrock there. Furthermore, there are other areas with particularly clear hematite detections that likely formed in a similar manner as Vera Rubin ridge. We end this paper with a discussion of lessons learned from this experience for using orbital data to guide rovers in the future.
Key Points
Areas on Vera Rubin ridge with deep ferric absorptions from orbit also have deep ferric absorptions in Curiosity spectral data sets
Ferric phases are more widespread on Mt. Sharp than originally reported. Diagenesis deepened ferric absorptions in several locations
Combining orbital and in situ observations enhances planetary exploration
Sedimentary amorphous and nanocrystalline materials are abundant on Mars, but their formation conditions are poorly understood due in part to instrument limitations and the lack of knowledge about ...terrestrial sedimentary amorphous and nanocrystalline material compositions and structures. Additionally, it is surprising that the Curiosity rover finds these metastable phases preserved in ancient (3–4 Gya) rocks in Gale crater. Here, we use X‐ray diffraction and high‐resolution transmission electron microscopy to investigate the X‐ray amorphous weathering products found in soils, sediments, and paleosols from Mars‐relevant mafic to intermediate volcanic terrains altered under different climates. The X‐ray amorphous components of our samples are often complex mixtures of amorphous and nanocrystalline materials with compositions that vary at the nanometer‐scale, but are dominated by iron‐oxide, Al2O3, and SiO2, the proportions of which reflect large‐scale weathering conditions, such that those formed in warm and wet climates are deficient in more mobile cations, and those formed under cooler climates reflect restricted cation leaching. We also find high abundances (∼40 wt.%) of X‐ray amorphous weathering products in lithified and diagenetically altered volcanic soils that have been preserved over time scales of ∼107 years. These results have wide‐reaching implications for soil property and paleoclimate investigations on Earth and Mars, and suggest that amorphous and nanocrystalline materials are important, but overlooked components of some sedimentary rocks on Earth. Future investigations are needed to better understand the kinetics behind the transformation from amorphous and nanocrystalline to crystalline materials and the factors that allow their preservation on Earth and Mars.
Plain Language Summary
Amorphous and nanocrystalline weathering products are abundant across the surface of Mars. Like crystalline weathering products, amorphous and nanocrystalline weathering products can help inform about ancient weathering environments and conditions. Unfortunately, even on Earth, little is known about how formation conditions affect the chemical compositions and atomic structures of amorphous and nanocrystalline weathering products. Additionally, on Earth amorphous and nanocrystalline weathering products are thought to quickly convert to more stable crystalline minerals, and so it is surprising to find abundant amorphous and nanocrystalline materials in 3–4 billion year old rocks on Mars. This study attempts to address these knowledge gaps by examining the abundance, composition, and structure of amorphous and nanocrystalline weathering products in Mars analog soils, sediments, and 30–50 million year old sedimentary rocks from different weathering environments. We find that the compositions of the amorphous and nanocrystalline weathering products reflect large‐scale weathering conditions, and that amorphous and nanocrystalline weathering products are preserved in high abundances in our ∼107 year old sedimentary rocks. These findings indicate that amorphous and nanocrystalline weathering products can be used to help constrain past environments on Mars, and suggest that amorphous and nanocrystalline weathering products are overlooked components of some sedimentary rocks on Earth.
Key Points
X‐ray amorphous materials in our Mars‐analog samples are complex mixtures of amorphous and nanocrystalline weathering products
Amorphous and nanocrystalline weathering product compositions reflect the degree of chemical alteration of their surroundings
X‐ray amorphous materials are preserved at high abundances (∼40 wt%) over time scales of ∼107 years in lithified volcanic soils
The CheMin instrument on the Mars Science Laboratory rover Curiosity detected ubiquitous high abundances (∼15–70 wt%) of X‐ray amorphous components (AmCs) in ancient sedimentary rocks of Gale crater. ...Mechanisms and timing of formation for the AmCs are poorly constrained, and could include volcanic, impact, or aqueous processes. We explore trends in AmC composition and abundance, and look for systematic compositional variation between sites within Gale crater. AmC compositions were estimated indirectly based on bulk chemistry and the nature and abundance of the crystalline phases for 19 sedimentary rock samples. AmC abundances positively correlate with AmC SiO2 contents, and a mixing relationship appears to exist between SiO2‐rich and FeOT‐rich AmC endmembers. Endmember compositions are inconsistent with volcanic or impact glass alone, and so we conclude that the SiO2 and FeOT contents formed largely through aqueous processes. Cross‐cutting relationships and geologic context provide evidence that the most SiO2‐rich AmCs observed in Gale crater thus far may result from interactions with localized fluids during late diagenesis. AmCs with moderate to low SiO2 contents likely formed earlier (before or soon after sediment deposition). Thus, the AmC SiO2 and FeOT contents in Gale crater rocks represent mixtures of sedimentary materials formed over most of the sedimentary history of Gale crater, starting before the first sediments were deposited in the crater (late Noachian), and ending well after the youngest sediments were lithified (at least mid‐Hesperian). However, it remains unclear how these metastable minerals have persisted through billions of years of diagenesis in Gale crater sediments.
Plain Language Summary
The CheMin instrument on the Mars Science Laboratory rover Curiosity detected ubiquitous high abundances (∼15–70 wt%) of amorphous materials in ancient sedimentary rocks of Gale crater. It is uncertain what geologic processes these materials represent (volcanic eruptions, impacts, or interactions with water), and when these materials were formed. Here we explore these possible formation mechanisms and their timing by estimating the chemical compositions of the amorphous materials, and looking for trends and variations in their compositions along the rover traverse. We find that amorphous iron‐ and silica‐rich materials formed mostly through interactions with water, and likely represent mixtures of chemical weathering products, chemical sediments, and cements that accumulated over time. We also find that some of the amorphous materials formed early on in the history of the crater, while others formed long after sediments were deposited and turned into rock, indicating that water persisted at Gale crater for ∼1 billion years. On Earth, it is thought that amorphous materials are readily converted into more crystalline materials in the presence of water, but it is unclear why this is not the case for Mars.
Key Points
X‐ray amorphous abundances are positively correlated with SiO2 content, and amorphous SiO2 and FeOT contents are anticorrelated
X‐ray amorphous SiO2 and FeOT contents in Gale crater sedimentary rocks largely represent multiple aqueous processes occurring over time
It is unclear how such metastable materials have persisted for billions of years
Noachian-aged Jezero crater is the only known location on Mars where clear orbital detections of carbonates are found in close proximity to clear fluvio-lacustrine features indicating the past ...presence of a paleolake; however, it is unclear whether or not the carbonates in Jezero are related to the lacustrine activity. This distinction is critical for evaluating the astrobiological potential of the site, as lacustrine carbonates on Earth are capable of preserving biosignatures at scales that may be detectable by a landed mission like the Mars 2020 rover, which is planned to land in Jezero in February 2021. In this study, we conduct a detailed investigation of the mineralogical and morphological properties of geological units within Jezero crater in order to better constrain the origin of carbonates in the basin and their timing relative to fluvio-lacustrine activity. Using orbital visible/near-infrared hyperspectral images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) along with high resolution imagery and digital elevation models, we identify a distinct carbonate-bearing unit, the “Marginal Carbonates,” located along the inner margin of the crater, near the largest inlet valley and the western delta. Based on their strong carbonate signatures, topographic properties, and location in the crater, we propose that this unit may preserve authigenic lacustrine carbonates, precipitated in the near-shore environment of the Jezero paleolake. Comparison to carbonate deposits from terrestrial closed basin lakes suggests that if the Marginal Carbonates are lacustrine in origin, they could preserve macro- and microscopic biosignatures in microbialite rocks like stromatolites, some of which would likely be detectable by Mars 2020. The Marginal Carbonates may represent just one phase of a complex fluvio-lacustrine history in Jezero crater, as we find that the spectral diversity of the fluvio-lacustrine deposits in the crater is consistent with a long-lived lake system cataloging the deposition and erosion of regional geologic units. Thus, Jezero crater may contain a unique record of the evolution of surface environments, climates, and habitability on early Mars.
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•Strong carbonate signatures occur along the western inner margin of Jezero crater.•Topographic and spectral properties are consistent with lake shore precipitates.•Marginal carbonate deposits have a high biosignature preservation potential.•Delta/fans show primary mineral trends in stratigraphy traceable to regional units.•A long-lived and habitable lake system may have persisted in Jezero.
Orbital imagery and spectroscopy at Mars have identified a variety of deposits potentially consistent with volcanic tephra formed during explosive volcanic eruptions, and some of these deposits may ...have formed due to water‐ or ice‐magma interactions during phreatomagmatic eruptions. If this is the case, these deposits could serve as an additional record of past water on Mars. Previous work has demonstrated that phreatomagmatic tephra is characterized by much lower crystallinities than tephras from other types of eruptions. We hypothesize that crystallinity could be inferred remotely using spectroscopy; however, tephra spectral properties have not been directly linked to their mineralogy. Here, we use Mars analog tephra samples to investigate if eruption styles and the past presence of water during the eruption of possible volcanic deposits on Mars can be determined using orbital spectroscopy. Visible/near‐infrared (VNIR) reflectance and thermal infrared (TIR) emission spectra were collected of basaltic volcanic tephras sourced from a range of eruption styles and deposit types on Earth. Our research demonstrates that, TIR and VNIR data are both sufficient to detect increased glass abundances in volcanic deposits, potentially indicating volatile interactions during an eruption, and that glass‐poor tephras have distinct TIR properties that can be used to infer tephra type (e.g., ignimbrite vs. scoria). Combining VNIR and TIR orbital data for analysis based on our new laboratory spectral endmember library may allow a reevaluation of Martian volcanic and volatile histories using current and future planetary orbital and in situ spectral datasets.
Plain Language Summary
Volcanism is a common process across the solar system. Eruptions can become explosive after interactions with water, and the search for current or past water is critical to planetary exploration. Collecting planetary samples to understand what types of eruptions created the volcanic rocks present is not always possible, so we investigate a method for determining volcanic eruption styles that could be completed from orbit. Spectrometers are common instruments on orbiters and can measure the reflection and emission of light from surface materials, including glass. Glass forms in volcanic eruptions when magma quickly cools before minerals can form. We demonstrated that, volcanic deposits from eruptions that were explosive due to interaction with water were glass‐rich and could be distinguished from deposits created in other types of eruptions using data similar to those collected by satellites at Mars. Alteration due to water in the local environment just after eruption is also detectable from orbit. Applying these results to existing or future satellite datasets will provide insight into volcanic eruption styles and environments on planets like Mars.
Key Points
The presence of significant glass in volcanic tephras can indicate formation in an explosive phreatomagmatic eruption
Visible/near‐infrared (VNIR) and thermal‐infrared (TIR) spectroscopy can be used together to determine the eruption and cooling history of tephras
A combination of VNIR and TIR orbital spectral datasets would provide insight into the volcanic and volatile histories of Mars and other planets
On February 18, 2021 NASA's Perseverance rover landed in Jezero crater, located at the northwestern edge of the Isidis basin on Mars. The uppermost surface of the present‐day crater floor is ...dominated by a distinct geologic assemblage previously referred to as the dark‐toned floor. It consists of a smooth, dark‐toned unit overlying and variably covering light‐toned, roughly eroded deposits showing evidence of discrete layers. In this study, we investigated the stratigraphic relations between materials that comprise this assemblage, the main western delta deposit, as well as isolated mesas located east of the main delta body that potentially represent delta remnants. A more detailed classification and differentiation of crater floor units in Jezero and determination of their relative ages is vital for the understanding of the geologic evolution of the crater system, and determination of the potential timeline and environments of habitability. We have investigated unit contacts using topographic profiles and DEMs as well as the distribution of small craters and fractures on the youngest portions of the crater floor. Our results indicate that at least some of the deltaic deposition in Jezero postdates emplacement of the uppermost surface of the crater floor assemblage. The inferred age of the floor assemblage can therefore help to constrain the timing of the Jezero fluviolacustrine system, wherein at least some lake activity postdates the age of the uppermost crater floor. We present hypotheses that can be tested by Perseverance and can be used to advance our knowledge of the geologic evolution of the area.
Plain Language Summary
On February 18, 2021 NASA's Perseverance rover landed in Jezero crater on Mars. In the past, the crater was filled with water, forming a lake, and in the western part of the crater an ancient delta is preserved. Part of the present‐day crater floor has been interpreted to represent a lava flow that was deposited after the lake dried out, meaning that the floor unit would be younger than the western delta. In order to understand how the Jezero crater lake has developed over time, including the potential timeline and environments of habitability, it is necessary to work out the relations between the geologic units in Jezero crater. In this work, we have analyzed orbital images of Jezero crater and reveal how the crater floor and delta deposits relate to each other in time. Our results show that at least some of the deltaic deposits in Jezero overlie the youngest crater floor unit(s). It is therefore possible to learn broadly when fluvial activity in the crater has been effective from the age of the crater floor. Our work presents hypotheses that can be tested by Perseverance to advance our knowledge of how the area has evolved geologically over time.
Key Points
We have studied stratigraphic relations between geologic units in Jezero crater for determination of relative age relations in the crater
Topographic profiles and digital elevation models indicate that the western delta is on top of the youngest crater floor unit(s)
We thus place constraints on the timeline of fluvial‐lacustrine activity in Jezero crater
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