The water and fluorine content of 4 Vesta Sarafian, Adam R.; Nielsen, Sune G.; Marschall, Horst R. ...
Geochimica et cosmochimica acta,
12/2019, Letnik:
266
Journal Article
Recenzirano
The processes that controlled accretion of water and volatiles to the inner solar system remain enigmatic, because it is difficult to determine the absolute concentrations of volatile elements in ...planetary bodies. In this contribution we study rare unequilibrated eucrites derived from the asteroid 4 Vesta, to determine the water and fluorine content of this asteroid by measuring the volatile content of pyroxene. Common thermal metamorphism in most equilibrated eucrites would have diffusively reset magmatic volatile contents. The unequilibrated eucrites are, therefore, the most suitable samples to determine primary magmatic volatile contents of 4 Vesta. We find H2O and F contents in pyroxenes of 4–11 µg/g and 0.12–0.23 µg/g. We also determine a H2O partition coefficient for clinopyroxene and melt equilibrated at 0.1 MPa of DH2O = 0.1, which is higher than values previously reported for higher pressures. The higher compatibility of H2O in this experiment could partially be due to high OH/H2O ratio at the low total water contents in this experimental charge, but only further more detailed experiments will fully delineate the reasons for the more compatible behavior for water at lower pressures. However, given the lack of H2O partitioning data at low pressures we conclude that our 0.1 MPa experiment is the most appropriate to calculate magmatic water contents for melt in equilibrium with eucrite pyroxene. After using appropriate partition coefficients we calculate melt concentrations of 50–70 µg/g H2O and 1.5–2.4 µg/g F. In turn, these are converted into bulk 4 Vesta water and F contents of 10–70 µg/g H2O and 0.3–2 µg/g F by assuming eucrite formation via either mantle partial melting or extraction from a magma ocean. We also measure the D/H of the clinopyroxenes and show that these are identical to the results of previous studies that reported D/H in eucrite apatite. These values match those found in carbonaceous chondrites suggesting that water in 4 Vesta accreted from carbonaceous chondrites and not from cometary material.
– Sacramento Wash 005 (SaW) 005, Meteorite Hills 00428 (MET) 00428, and Mount Howe 88403 (HOW) 88403 are S‐rich Fe,Ni‐rich metal meteorites with fine metal structures and homogeneous troilite. We ...compare them with the H‐metal meteorite, Lewis Cliff 88432. Phase diagram analyses suggest that SaW 005, MET 00428, and HOW 88403 were liquids at temperatures above 1350 °C. Tridymite in HOW 88403 constrains formation to a high‐temperature and low‐pressure environment. The morphology of their metal‐troilite structures may suggest that MET 00428 cooled the slowest, SaW 005 cooled faster, and HOW 88403 cooled the quickest. SaW 005 and MET 00428 contain H‐chondrite like silicates, and SaW 005 contains a chondrule‐bearing inclusion that is texturally and compositionally similar to H4 chondrites. The compositional and morphological similarities of SaW 005 and MET 00428 suggest that they are likely the result of impact processing on the H‐chondrite parent body. SaW 005 and MET 00428 are the first recognized iron‐ and sulfide‐rich meteorites, which formed by impact on the H‐chondrite parent body, which are distinct from the IIE‐iron meteorite group. The morphological and chemical differences of HOW 88403 suggest that it is not from the H‐chondrite body, although it likely formed during an impact on a chondritic parent body.
The Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) is a robotic arm-mounted instrument onboard NASA’s
Perseverance
rover. SHERLOC combines imaging ...via two cameras with both Raman and fluorescence spectroscopy to investigate geological materials at the rover’s Jezero crater field site. SHERLOC requires
in situ
calibration to monitor the health and performance of the instrument. These calibration data are critically important to ensure the veracity of data interpretation, especially considering the extreme martian environmental conditions where the instrument operates. The SHERLOC Calibration Target (SCT) is located at the front of the rover and is exposed to the same atmospheric conditions as the instrument. The SCT includes 10 individual targets designed to meet all instrument calibration requirements. An additional calibration target is mounted inside the instrument’s dust cover. The targets include polymers, rock, synthetic material, and optical pattern targets. Their primary function is calibration of parameters within the SHERLOC instrument so that the data can be interpreted correctly. The SCT was also designed to take advantage of opportunities for supplemental science investigations and includes targets intended for public engagement. The exposure of materials to martian atmospheric conditions allows for opportunistic science on extravehicular suit (i.e., “spacesuit”) materials. These samples will be used in an extended study to produce direct measurements of the expected service lifetimes of these materials on the martian surface, thus helping NASA facilitate human exploration of the planet. Other targets include a martian meteorite and the first geocache target to reside on another planet, both of which increase the outreach and potential of the mission to foster interest in, and enthusiasm for, planetary exploration. During the first 200 sols (martian days) of operation on Mars, the SCT has been analyzed three times and has proven to be vital in the calibration of the instrument and in assisting the SHERLOC team with interpretation of
in situ
data.
The low-temperature form of CuFe sub(2)S sub(3), cubanite, has been identified in the CI chondrite and NASA Stardust mission collections. The presence of this mineral constrains the maximum ...temperature to 210 degree C since the time of its formation. However, until now, the conditions under which cubanite forms were less well constrained. In order to refine the history of the time-varying, low-temperature fluids which existed on the CI-chondrite parent body and Comet 81P/Wild 2 (Wild 2), we synthesized cubanite. The experimental synthesis of this mineral was achieved, for the first time, under low-temperature aqueous conditions relevant to the CI-chondrite parent body. Using a variant of in situ hydrothermal recrystallization, cubanite formed in aqueous experiments starting with temperatures of 150 and 200 degree C, pH approximately 9, and oxygen fugacities corresponding to the iron-magnetite buffer. The composition and structure of the cubanite were determined using electron microprobe and transmission electron microscopy techniques, respectively. The combined compositional, crystallographic, and experimental data allow us to place limits on the conditions under which the formation of cubanite is feasible, which in turn constrains the nature of the fluid phase on the CI-chondrite parent body and Wild 2 when cubanite was forming.
Inner Solar System bodies are depleted in volatile elements relative to chondrite meteorites, yet the source(s) and mechanism(s) of volatile-element depletion and/or enrichment are poorly ...constrained. The timing, mechanisms and quantities of volatile elements present in the early inner Solar System have vast implications for diverse processes, from planetary differentiation to the emergence of life. We report major, trace and volatile-element contents of a glass bead derived from the D'Orbigny angrite, the hydrogen isotopie composition of this glass bead and that of coexisting olivine and silicophosphates, and the ²⁰⁷Pb—²⁰⁶Pb age of the silicophosphates, 4568 ±20 Ma. We use volatile saturation models to demonstrate that the angrite parent body must have been a major body in the early inner Solar System. We further show via mixing calculations that all inner Solar System bodies accreted volatile elements with carbonaceous chondrite H and N isotope signatures extremely early in Solar System history. Only a small portion (if any) of comets and gaseous nebular H species contributed to the volatile content of the inner Solar System bodies. This article is part of the themed issue 'The origin, history and role of water in the evolution of the inner Solar System'.
Sulfur plays a major role in martian geochemistry and sulfate minerals are important repositories of water. However, their hydration states on Mars are poorly constrained. Therefore, understanding ...the hydration and distribution of sulfate minerals on Mars is important for understanding its geologic, hydrologic, and atmospheric evolution as well as its habitability potential. NASA's Perseverance rover is currently exploring the Noachian‐age Jezero crater, which hosts a fan‐delta system associated with a paleolake. The crater floor includes two igneous units (the Séítah and Máaz formations), both of which contain evidence of later alteration by fluids including sulfate minerals. Results from the rover instruments Scanning Habitable Environments with Raman and Luminescence for Organics and Chemistry and Planetary Instrument for X‐ray Lithochemistry reveal the presence of a mix of crystalline and amorphous hydrated Mg‐sulfate minerals (both MgSO4·3–5H2O and possible MgSO4·H2O), and anhydrous Ca‐sulfate minerals. The sulfate phases within each outcrop may have formed from single or multiple episodes of water activity, although several depositional events seem likely for the different units in the crater floor. Textural and chemical evidence suggest that the sulfate minerals most likely precipitated from a low temperature sulfate‐rich fluid of moderate pH. The identification of approximately four waters puts a lower constraint on the hydration state of sulfate minerals in the shallow subsurface, which has implications for the martian hydrological budget. These sulfate minerals are key samples for future Mars sample return.
Plain Language Summary
The history of water on Mars is a puzzle that is of interest to scientists as well as the general public. Mars currently has water in the form of ice at the poles, trace amounts of gas in the atmosphere, and an unknown amount beneath the surface as ground water, bound in minerals, and in ice. However, there is strong evidence that ancient Mars may have had long‐lived streams, rivers, and lakes. There is still much to learn about what Mars was like and how it transformed over time. One approach is to study the inventory of water at different times. In this work, we report the presence of hydrated magnesium sulfate (similar to Epsom salts) and dehydrated calcium sulfate that were formed by water flowing through cracks in volcanic rocks at the bottom of the 3.8‐billion‐year‐old Jezero crater. These hydrated minerals trap water within themselves and record the history of how and when they formed. Returning samples of these minerals to Earth would allow researchers to explore the history of Mars' water and climate, and possibly evidence of ancient life with the most sensitive instruments possible.
Key Points
Sulfate phases detected by Scanning Habitable Environments with Raman and Luminescence for Organics and Chemistry and PIXL in igneous units consists of crystalline/amorphous Mg‐sulfate minerals with 3–5 waters and anhydrous Ca‐sulfate minerals
Hydration of sulfate minerals sets a lower constraint on how much subsurface water is stored in sulfate minerals
The sulfate minerals of Jezero crater floor were deposited in moderate pH, likely at low temperature, and during several episodes
Exposure to solar wind irradiation and micrometeorite impacts alter the properties of regolith materials exposed on airless bodies. However, estimates of space weathering rates for asteroid regoliths ...span many orders of magnitude. Timescales for space weathering processes on airless bodies can be anchored by analyzing surface samples returned by JAXA's Hayabusa mission to asteroid 25143 Itokawa. Constraints on timescales of solar flare particle track accumulation and formation of solar wind produced ion-damaged rims yield information on regolith dynamics.
Mineral grains in lunar and asteroidal regolith samples provide a unique record of their interaction with the space environment. Space weathering effects result from multiple processes including: ...exposure to the solar wind, which results in ion damage and implantation effects that are preserved in the rims of grains (typically the outermost 100 nm); cosmic ray and solar flare activity, which result in track formation; and impact processes that result in the accumulation of vapor-deposited elements, impact melts and adhering grains on particle surfaces. Determining the rate at which these effects accumulate in the grains during their space exposure is critical to studies of the surface evolution of airless bodies. Solar flare energetic particles (mainly Fe-group nuclei) have a penetration depth of a few millimeters and leave a trail of ionization damage in insulating materials that is readily observable by transmission electron microscope (TEM) imaging. The density of solar flare particle tracks is used to infer the length of time an object was at or near the regolith surface (i.e., its exposure age). Track measurements by TEM methods are routine, yet track production rate calibrations have only been determined using chemical etching techniques e.g., 1, and references therein. We used focused ion beam-scanning electron microscope (FIB-SEM) sample preparation techniques combined with TEM imaging to determine the track density/exposure age relations for lunar rock 64455. The 64455 sample was used earlier by 2 to determine a track production rate by chemical etching of tracks in anorthite. Here, we show that combined FIB/TEM techniques provide a more accurate determination of a track production rate and also allow us to extend the calibration to solar flare tracks in olivine.
Space weathering processes such as solar wind irradiation and micrometeorite impacts are known to alter the the properties of regolith materials exposed on airless bodies. The rates of space ...weathering processes however, are poorly constrained for asteroid regoliths, with recent estimates ranging over many orders of magnitude. The return of surface samples by JAXA's Hayabusa mission to asteroid 25143 Itokawa, and their laboratory analysis provides "ground truth" to anchor the timescales for space weathering processes on airless bodies. Here, we use the effects of solar wind irradiation and the accumulation of solar flare tracks recorded in Itokawa grains to constrain the rates of space weathering and yield information about regolith dynamics on these timescales.
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