ORCID Profile
0000-0001-5210-4002
Current Organisation
University of Alberta
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Publisher: American Association for the Advancement of Science (AAAS)
Date: 13-07-2012
Abstract: Understanding the sources and the formation mechanisms of organic carbon compounds on Mars has implications for our understanding of the martian carbon cycle. Steele et al. (p. 212 , published online 24 May) present measurements of organic material in 11 martian meteorites, including the Tissint meteorite, which fell in the Moroccan desert in July 2011. Ten of the meteorites contain complex hydrocarbons encased within igneous minerals. The results imply that the organics formed as the magma melt crystallized and are thus of abiotic origin.
Publisher: Research Square Platform LLC
Date: 11-10-2021
DOI: 10.21203/RS.3.RS-592064/V1
Abstract: The Oort cloud is thought to be a reservoir of icy planetesimals and a source of long-period comets (LPCs) implanted from the outer Solar System during the time of giant planet formation. The presence of rocky ice-free bodies is much harder to explain. The rocky fraction in the Oort cloud is a key diagnostic of Solar System formation models as this ratio can distinguish between "massive" and "depleted" proto-asteroid belt scenarios and thus disentangle competing planet formation models. Objects of asteroidal appearance have been telescopically observed on LPC orbits, but from reflectance spectra alone it is uncertain whether they are asteroids or extinct comets. Here we report a first direct observation of a decimeter-sized rocky meteoroid on a retrograde LPC orbit (e ≈ 1.0, i = 121°). The ~2 kg object entered the atmosphere at 62 km/s. The associated fireball terminated at 46.5 km, 40 km deeper than cometary objects of similar mass and speed. During its flight, it experienced dynamic pressures of several MPa, comparable to meteorite-dropping fireballs. In contrast, cometary material measured by Rosetta have compressive strengths of ~1 kPa. The earliest fragmentation of this fireball occurred at kPa, indicating it had a minimum global strength well in excess of cometary. A numerical ablation model produces bulk density and ablation properties consistent with asteroidal meteoroids. We estimate the flux of rocky objects impacting Earth from the Oort cloud to be ~0.7 × 10 6 km 2 per year to a mass limit of 10 g. This is ~6% of the total flux of fireballs on LPC-orbits to these masses. Our results suggests there is a high fraction of asteroidal material in the Oort cloud at small sizes and gives support to migration-based dynamical models of the formation of the Solar System which predict that significant rocky material is implanted in the Oort cloud, a result not explained by traditional Solar System formation models.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 30-09-2022
Abstract: The Perseverance rover landed in Jezero crater, Mars, to investigate ancient lake and river deposits. We report observations of the crater floor, below the crater's sedimentary delta, finding that the floor consists of igneous rocks altered by water. The lowest exposed unit, informally named Séítah, is a coarsely crystalline olivine-rich rock, which accumulated at the base of a magma body. Magnesium-iron carbonates along grain boundaries indicate reactions with carbon dioxide-rich water under water-poor conditions. Overlying Séítah is a unit informally named Máaz, which we interpret as lava flows or the chemical complement to Séítah in a layered igneous body. Voids in these rocks contain sulfates and perchlorates, likely introduced by later near-surface brine evaporation. Core s les of these rocks have been stored aboard Perseverance for potential return to Earth.
Publisher: Wiley
Date: 07-02-2022
Publisher: Springer Science and Business Media LLC
Date: 12-12-2022
Publisher: Mary Ann Liebert Inc
Date: 03-2012
Publisher: American Geophysical Union (AGU)
Date: 07-2023
DOI: 10.1029/2022JE007440
Abstract: The Máaz formation consists of the first lithologies in Jezero crater analyzed by the Mars 2020 Perseverance rover. This formation, investigated from Sols (Martian days) 1 to 201 and from Sols 343 to 382, overlies the Séítah formation (previously described as an olivine‐rich cumulate) and was initially suggested to represent an igneous crater floor unit based on orbital analyses. Using SuperCam data, we conducted a detailed textural, chemical, and mineralogical analyses of the Máaz formation and the Content member of the Séítah formation. We conclude that the Máaz formation and the Content member are igneous and consist of different lava flows and/or possibly pyroclastic flows with complex textures, including vesicular and non‐vesicular rocks with different grain sizes. The Máaz formation rocks exhibit some of the lowest Mg# (=molar 100 × MgO/MgO + FeO) of all Martian igneous rocks analyzed so far (including meteorites and surface rocks) and show similar basaltic to basaltic‐andesitic compositions. Their mineralogy is dominated by Fe‐rich augite to possibly ferrosilite and plagioclase, and minor phases such as Fe‐Ti oxides and Si‐rich phases. They show a broad ersity of both compositions and textures when compared to Martian meteorites and other surface rocks. The different Máaz and Content lava or pyroclastic flows all originate from the same parental magma and/or the same magmatic system, but are not petrogenetically linked to the Séítah formation. The study of returned Máaz s les in Earth‐based laboratories will help constrain the formation of these rocks, calibrate Martian crater counting, and overall, improve our understanding of magmatism on Mars.
Publisher: American Geophysical Union (AGU)
Date: 06-2023
DOI: 10.1029/2022JE007474
Abstract: The first s les collected by the Mars 2020 mission represent units exposed on the Jezero Crater floor, from the potentially oldest Séítah formation outcrops to the potentially youngest rocks of the heavily cratered Máaz formation. Surface investigations reveal landscape‐to‐microscopic textural, mineralogical, and geochemical evidence for igneous lithologies, some possibly emplaced as lava flows. The s les contain major rock‐forming minerals such as pyroxene, olivine, and feldspar, accessory minerals including oxides and phosphates, and evidence for various degrees of aqueous activity in the form of water‐soluble salt, carbonate, sulfate, iron oxide, and iron silicate minerals. Following s le return, the compositions and ages of these variably altered igneous rocks are expected to reveal the geophysical and geochemical nature of the planet's interior at the time of emplacement, characterize martian magmatism, and place timing constraints on geologic processes, both in Jezero Crater and more widely on Mars. Petrographic observations and geochemical analyses, coupled with geochronology of secondary minerals, can also reveal the timing of aqueous activity as well as constrain the chemical and physical conditions of the environments in which these minerals precipitated, and the nature and composition of organic compounds preserved in association with these phases. Returned s les from these units will help constrain the crater chronology of Mars and the global evolution of the planet's interior, for understanding the processes that formed Jezero Crater floor units, and for constraining the style and duration of aqueous activity in Jezero Crater, past habitability, and cycling of organic elements in Jezero Crater.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 30-09-2022
Abstract: 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 investigated 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 found 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 multistage cooling of a thick magma body.
Publisher: American Geophysical Union (AGU)
Date: 10-2023
DOI: 10.1029/2022JE007444
Abstract: In situ geologic context mapping (GXM) based on rover and helicopter observations provides documentation of a nearly continuous record of geology and exposed surface structure over a 120 m‐wide corridor along the traverse of the Mars 2020 /Perseverance rover. The results record the geologic context of Mars 2020 c aign sites and s le sites including the local extent of bedrock outcrops, stratigraphy, attitude, and structure from imaging and rover‐based remote sensing, and outcrop lithology based on in situ proximity science. Mapping identifies a sequence of igneous lithologies including: (1) early mafic, possibly intrusive, rocks (2) pervasively fractured and deeply altered massive bedrock of undetermined protolith (3) buried and exhumed lava flows with pahoehoe and aa textures (4) several varieties of regolith and (5) small impact craters.
Publisher: Elsevier BV
Date: 06-2019
Publisher: American Geophysical Union (AGU)
Date: 06-2023
DOI: 10.1029/2022JE007613
Abstract: The Mars 2020 Perseverance rover landed in Jezero crater on 18 February 2021. After a 100‐sol period of commissioning and the Ingenuity Helicopter technology demonstration, Perseverance began its first science c aign to explore the enigmatic Jezero crater floor, whose igneous or sedimentary origins have been much debated in the scientific community. This paper describes the c aign plan developed to explore the crater floor's Máaz and Séítah formations and summarizes the results of the c aign between sols 100–379. By the end of the c aign, Perseverance had traversed more than 5 km, created seven abrasion patches, and sealed nine s les and a witness tube. Analysis of remote and proximity science observations show that the Máaz and Séítah formations are igneous in origin and composed of five and two geologic members, respectively. The Séítah formation represents the olivine‐rich cumulate formed from differentiation of a slowly cooling melt or magma body, and the Máaz formation likely represents a separate series of lava flows emplaced after Séítah. The Máaz and Séítah rocks also preserve evidence of multiple episodes of aqueous alteration in secondary minerals like carbonate, Fe/Mg phyllosilicates, sulfates, and perchlorate, and surficial coatings. Post‐emplacement processes tilted the rocks near the Máaz‐Séítah contact and substantial erosion modified the crater floor rocks to their present‐day expressions. Results from this crater floor c aign, including those obtained upon return of the collected s les, will help to build the geologic history of events that occurred in Jezero crater and provide time constraints on the formation of the Jezero delta.
Publisher: Elsevier BV
Date: 02-2010
Publisher: Authorea, Inc.
Date: 08-07-2023
DOI: 10.22541/ESSOAR.168882010.05601670/V1
Abstract: During the NASA Perseverance rover’s exploration of the Jezero crater floor, purple-hued coatings were commonly observed on rocks. These features likely record past water-rock-atmosphere interactions on the crater floor, and understanding their origin is important for constraining timing of water activity and habitability at Jezero. Here we characterize the morphologic, chemical, and spectral properties of the crater floor rock coatings using color images, visible/near-infrared reflectance spectra, and chemical data from the Mastcam-Z and SuperCam instruments. We show that coatings are common and compositionally similar across the crater floor, and consistent with a mixture of dust, fine regolith, sulfates, and ferric oxides indurated as a result of one or more episodes of widespread surface alteration. All coatings exhibit a similar smooth homogenous surface with variable thickness, color, and spatial extent on rocks, likely reflecting variable oxidation and erosional expressions related to formation and/or exposure age. Coatings unconformably overlie eroded natural rock surfaces, suggesting relatively late deposition that may represent one of the last aqueous episodes on the Jezero crater floor. While more common at Jezero, these coatings may be consistent with rock coatings previously observed in-situ at other landing sites and may be related to duricrust formation, suggesting a global alteration process on Mars that is not unique to Jezero. The Perseverance rover likely s led these rock coatings on the crater floor and results from this study could provide important context for future investigations by the Mars S le Return mission aimed at constraining the geologic and aqueous history of Jezero crater.
No related grants have been discovered for Christopher Herd.