Kevin Mckeegan

• Ph.D., Physics, Washington Uni
• University of California, Los Angeles

Solar wind Fe and Mg fluences (atoms/cm ² ) were measured from Genesis collectors. Fe and Mg have similar first ionization potentials and solar wind Fe/Mg should equal the solar ratio. Solar wind Fe/Mg is a more valid measure of solar composition than CI chondrites and can be measured more accurately than spectroscopic photospheric abundances. Mg a...

Crystallization of the lunar magma ocean yielded a chemically unique liquid residuum named KREEP. This component is expressed as a large patch on the near side of the Moon, and a possible smaller patch in the northwest portion of the Moon's South Pole-Aitken basin on the far side. Thermal models estimate that the crystallization of the lunar magma...

Crystallization of the lunar magma ocean yielded a chemically unique liquid residuum named KREEP. This component is expressed as a large patch on the near side of the Moon and a possible smaller patch in the northwest portion of the Moon’s South Pole-Aitken basin on the far side. Thermal models estimate that the crystallization of the lunar magma o...

The Moon has had a complex history, with evidence of its primary crust formation obscured by later impacts. Existing U-Pb dates of >500 zircons from several locations on the lunar nearside reveal a pronounced age peak at 4.33 billion years (Ga), suggesting a major, potentially global magmatic event. However, the precision of existing geochronology...

Oxygen 3‐isotope ratios of magnetite and carbonates in aqueously altered carbonaceous chondrites provide important clues to understanding the evolution of the fluid in the asteroidal parent bodies. We conducted oxygen 3‐isotope analyses of magnetite, dolomite, and breunnerite in two sections of asteroid Ryugu returned samples, A0058 and C0002, usin...

A synthetic laser ruby crystal (HD-LR1) is introduced as a new matrix-matched reference material for secondary ionization mass spectrometry (SIMS) analysis of oxygen isotopes in corundum. Laser fluorination isotope ratio...

The UCLA Cosmochemistry Database was initiated as part of a data-rescue and -storage project aimed at archiving a variety of cosmochemical data acquired at University of California, Los Angeles (UCLA). The data collection includes elemental compositions of extraterrestrial materials analyzed by UCLA cosmochemists over the last five decades. The ana...

We report Nd and Sm isotopic compositions of four samples of Ryugu returned by the Hayabusa2 mission, including “A” (first touchdown) and “C” (second touchdown) samples, and several carbonaceous chondrites to evaluate potential genetic relationships between Ryugu and known chondrite groups and track the cosmic ray exposure history of Ryugu. We reso...

Zircons are found in extraterrestrial rocks from the Moon, Mars, and some differentiated meteorite parent-bodies. These zircons are rare, often of small size, and have been affected by neutron capture induced by cosmic ray exposure. The application of the ¹⁷⁶Lu–¹⁷⁶Hf decay system to zircons from planetary bodies such as the Moon can help establish...

Studies of material returned from Cb asteroid Ryugu have revealed considerable mineralogical and chemical heterogeneity, stemming primarily from brecciation and aqueous alteration. Isotopic anomalies could have also been affected by delivery of exogenous clasts and aqueous mobilization of soluble elements. Here, we show that isotopic anomalies for...

We present oxygen isotopic analyses of fragments of the near-Earth C b -type asteroid Ryugu returned by the Hayabusa2 spacecraft that reinforce the close correspondence between Ryugu and CI chondrites. Small differences between Ryugu samples and CI chondrites in Δ ′ 17 O can be explained at least in part by contamination of the latter by terrestria...

Preliminary analyses of asteroid Ryugu samples show kinship to aqueously altered CI (Ivuna-type) chondrites, suggesting similar origins. We report identification of C-rich, particularly primitive clasts in Ryugu samples that contain preserved presolar silicate grains and exceptional abundances of presolar SiC and isotopically anomalous organic matt...

The Hayabusa2 spacecraft explored asteroid Ryugu and brought its surface materials to Earth. Ryugu samples resemble Ivuna-type (CI) chondrites—the most chemically primitive meteorites—and contain secondary phyllosilicates and carbonates, which are indicative of aqueous alteration. Understanding the conditions (such as temperature, redox state and f...

As the Sun was forming, calcium–aluminum‐rich inclusions (CAIs) were the first rocks to have condensed in the hottest regions of the solar nebula disk. Carbonaceous chondrites (CCs) contain abundant CAIs but are thought to have accreted in the outer Solar System, requiring that CAIs must have been transported outward. Curiously, CAIs are rare in or...

Rock fragments of the Cb-type asteroid Ryugu returned to Earth by the JAXA Hayabusa2 mission share mineralogical, chemical, and isotopic properties with the Ivuna-type (CI) carbonaceous chondrites. Similar to CI chondrites, these fragments underwent extensive aqueous alteration and consist predominantly of hydrous minerals likely formed in the pres...

Oxygen, magnesium, and silicon isotopic abundances in Vigarano 1623‐5 were studied using secondary ion mass spectrometry to investigate correlations between isotopic and petrologic properties of this unique forsterite‐bearing FUN inclusion. Vigarano 1623‐5 displays large, correlated mass‐dependent fractionation effects, tightly linked to mineralogy...

Samples from asteroid Ryugu returned by the Hayabusa2 mission contain evidence of extensive alteration by aqueous fluids and appear related to the CI chondrites. To understand the sources of the fluid and the timing of chemical reactions occurring during the alteration processes, we investigated the oxygen, carbon and ⁵³Mn–⁵³Cr systematics of carbo...

The delivery of water to the inner Solar System, including Earth, is still a debated topic. A preferential role for hydrated asteroids in this process is supported by isotopic measurements. Carbonaceous chondrite (CC) meteorites represent our main source of information about these volatile-rich asteroids. However, the destruction of weaker material...

The extraterrestrial materials returned from asteroid (162173) Ryugu consist predominantly of low-temperature aqueously formed secondary minerals and are chemically and mineralogically similar to CI (Ivuna-type) carbonaceous chondrites. Here, we show that high-temperature anhydrous primary minerals in Ryugu and CI chondrites exhibit a bimodal distr...

Initial analyses showed that asteroid Ryugu’s composition is close to CI (Ivuna-like) carbonaceous chondrites (CCs) – the chemically most primitive meteorites, characterized by near-solar abundances for most elements. However, some isotopic signatures (for example, Ti, Cr) overlap with other CC groups, so the details of the link between Ryugu and t...

Little is known about the origin of the spectral diversity of asteroids and what it says about conditions in the protoplanetary disk. Here we show that samples returned from Cb-type asteroid Ryugu have Fe isotopic anomalies indistinguishable from Ivuna-type (CI) chondrites, which are distinct from all other carbonaceous chondrites. Iron isotopes, t...

We have conducted a NanoSIMS-based search for presolar material in samples recently returned from C-type asteroid Ryugu as part of JAXA's Hayabusa2 mission. We report the detection of all major presolar grain types with O- and C-anomalous isotopic compositions typically identified in carbonaceous chondrite meteorites: 1 silicate, 1 oxide, 1 O-anoma...

Volatile and organic-rich C-type asteroids may have been one of the main sources of Earth’s water. Our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but the meteorite record is biased: only the strongest types survive atmospheric entry and are then modified by interaction with the terrestrial environ...

We have conducted a NanoSIMS-based search for presolar material in samples recently returned from C-type asteroid Ryugu as part of JAXAʼs Hayabusa2 mission. We report the detection of all major presolar grain types with O-and C-anomalous isotopic compositions typically identified in carbonaceous chondrite meteorites: 1 silicate, 1 oxide, 1 O-anomal...

Samples from asteroid Ryugu returned by the Hayabusa2 mission contain evidence of extensive alteration by aqueous fluids and appear related to the CI chondrites. To understand the sources of the fluid and the timing of chemical reactions occurring during the alteration processes, we investigated the oxygen, carbon, and ⁵³ Mn- ⁵³ Cr systematics of c...

The surface ecosystem of the Precambrian Earth was dominated by marine, planktonic and benthic phototrophic microorganisms, most prominently stromatolite-forming cyanobacteria, anoxygenic photosynthetic bacteria, and associated microbes. Although coupling the early microfossil record to physiologically definitive geochemical and isotopic signatures...

Moderately volatile elements (MVEs) are variably depleted in planetary bodies, reflecting the imprints of nebular and planetary processes. Among MVEs, Na, K, and Rb are excellent tracers for unraveling the history of MVE depletion in planetary bodies because they have similar geochemical behaviors but can be chemically fractionated by evaporation a...

We present elemental abundance data of C, N, O, Na, Mg, Al, Ca, and Cr in Genesis silicon targets. For Na, Mg, Al, and Ca, data from three different solar wind (SW) regimes are also presented. Data were obtained by backside depth profiling using secondary ion mass spectrometry. The accuracy of these measurements exceeds those obtained by in situ ob...

The timing of important events in the early history of the solar system can be established by using the decay of the short-lived radionuclide ⁵³Mn to stable ⁵³Cr. Carbonate minerals found in meteorite samples can be dated using this system provided that an accurate and precise value for the Mn/Cr ratio can be established. However, the ion yields of...

The timing of important events in the early history of the solar system can be established by using the decay of the short-lived radionuclide ⁵³Mn to stable ⁵³Cr. Carbonate minerals found in meteorite samples can be dated using this system provided that an accurate and precise value for the Mn/Cr ratio can be established. However, the ion yields of...

Recent isotopic and paleomagnetic data point to a possible connection between carbonaceous chondrites and differentiated planetary materials, suggesting the existence, perhaps ephemeral, of transitional objects with a layered structure whereby a metal-rich core is enclosed by a silicate mantle, which is itself overlain by a crust containing an oute...

Significance In spite of magnetic and isotopic evidence revealing connections between the most primitive outer Solar System materials and differentiated bodies with a layered structure akin to terrestrial planets, the meteoritic record lacks samples that document the initiation of partial melting and the onset of planetary differentiation. Here, we...

One way to go back in time to the formation of the solar system is to study meteorites. We can learn about the materials that formed the solar system and the processes that occurred during and after the formation of asteroids and planets by studying the mineralogy, chemistry, and isotopic compositions of meteorites. A particularly interesting group...

The assimilation of sulfate by Martian melts could explain the highly oxidized state of some Martian nakhlite meteorites, such as those paired with MIL 03346 (MIL 090030, MIL 090032, and MIL 090136). Here, a combination of new sulfur isotope data, mineral composition and abundance data, and consideration of mineral textures is used to link assimila...

Oxygen, magnesium, and silicon isotopic compositions in the mineralogically complex, ultrarefractory (UR) calcium-aluminum-rich inclusion (CAI) E101.1 from the reduced CV3 chondrite Efremovka confirm that E101.1 is a compound CAI composed of several lithological units that were once individual CAIs, free-floating in the solar protoplanetary disk. E...

Asteroids and comets are the remnants of the swarm of planetesimals from which the planets ultimately formed, and they retain records of processes that operated prior to and during planet formation. They are also likely the sources of most of the water and other volatiles accreted by Earth. In this review, we discuss the nature and probable origins...

We compare element and isotopic fractionations measured in solar wind samples collected by NASA's Genesis mission with those predicted from models incorporating both the ponderomotive force in the chromosphere and conservation of the first adiabatic invariant in the low corona. Generally good agreement is found, suggesting that these factors are co...

We compare element and isotopic fractionations measured in solar wind samples collected by NASA's Genesis mission with those predicted from models incorporating both the ponderomotive force in the chromosphere and conservation of the first adiabatic invariant in the low corona. Generally good agreement is found, suggesting that these factors are co...

A radio-frequency plasma ion source, the Hyperion-II, has been commissioned on a CAMECA ims1290, a high resolution/high transmission secondary ion mass spectrometer at UCLA. Performance characteristics (e.g., beam density, spot size, etc.) of the primary oxygen beam are documented and application to isotopic analyses requiring high lateral resoluti...

This paper describe the robustness of photochemical trend recorded in archean sediment, during their journey in the sublithospheric mantle and their entrappement by their hoste diamond. Each mine is characterized by a specific ∆33S/∆36S

This corrects the article DOI: 10.1038/ncomms11977.

The short-lived radionuclide decays to Cr providing a relative chronometer for dating the formation of Mn-rich minerals in meteorites. Secondary ion mass spectrometry (SIMS) has been extensively used for in situ dating of meteoritic olivine and carbonate by the - system, however a significant analytical challenge has been realising accurate measure...

The significant degradation that fossilized biomolecules may experience during burial makes it challenging to assess the biogenicity of organic microstructures in ancient rocks. Here we investigate the molecular signatures of 1.88 Ga Gunflint organic microfossils as a function of their diagenetic history. Synchrotron-based XANES data collected in s...

The apparent lack of plate tectonics on all terrestrial planets other than Earth has been used to support the notion that for most planets, once a primitive crust forms, the crust and mantle evolve geochemically-independent through time. This view has had a particularly large impact on models for the evolution of Mars and its silicate interior. Rec...

We searched for Cr-bearing inclusions in IVA iron in an attempt to find bulk Cr concentrations and volatile abundances during fractional crystallizations.

The CAI Egg 6 has typical 10Be/9Be, but not the predicted excess 138La. Either 10Be was not produced by solar protons or there were no 20 MeV protons.

Ion microprobe elemental and isotopic determinations can be precise but difficult to quantify. Error is introduced when the reference material and the sample to be analysed have different compositions. Mitigation of such “matrix effects” is possible using ion implants. If a compositionally homogeneous reference material is available which is “matri...

The Bibi-Maryam pluton crops out in the Sistan suture zone, eastern Iran. This pluton is a 1.5 × 2 km stock composed of leucocratic tonalite, granodiorite and granite. U-Pb zircon geochronology of a leucogranite indicates an emplacement age of 58.6 ± 2.1 Ma (95% confidence). The Bibi-Maryam rock suite is sodic with elevated Na2O/K2O (2.9 to 5.5), S...

The geochemistry of Martian meteorites provides a wealth of information about the solid planet and the surface and atmospheric processes that occurred on Mars. The degree to which Martian magmas may have assimilated crustal material, thus altering the geochemical signatures acquired from their mantle sources, is unclear. This issue features promine...

A method to quantitatively determine the fluences of shallowly-implanted solar wind ions returned to Earth by the Genesis Discovery mission is described. Through backside depth-profiling, we recover nearly complete depth profiles of implanted solar wind for several nonvolatile elements, including Mg, Al, Ca, Cr, and, to a lesser extent, Na, in sili...

We present bulk SW and SW regime elemental abundances measured in Genesis collectors comprising a wide range of masses and ionization properties.

We explore the mineralogical reservoirs of Cl in the martian surface by examining the Cl concentration and isotopic composition in apatite from NWA 7034.

We measured the oxygen-isotope compositions of residues within two impact craters from Stardust foils.

We discuss the enigmatic fluid-metasomatic melange, including Fe-metals, in the NWA 5738 eucrite, and a search for analogous stuff in ancient lunar rocks.

O, Mg, and Si isotopes in the ultrarefractory CAI E101.1 indicate coagulation and assimilation of proto-CAIs with different thermal histories in a 16O-poor gas.

The Cl-isotope composition of Mars differs from Earth, the Moon, and chondrites. Mantle samples are light; crustal materials are heavy. Mantle samples are unique.

We attempted to constrain the sources of short-lived radionuclides by inferring the oxygen isotopic compositions of the solar nebula prior to injections of supernova material.

In situ secondary ion mass spectrometry (SIMS) analyses of δ7Li, Li/Ca, and Mg/Ca were performed on five synthetic aragonite samples precipitated from seawater at 25°C at different rates. The compositions of δ7Li in bulk aragonites and experimental fluids were measured by multicollector inductively coupled plasma–mass spectrometry (MC-ICP-MS). Both...

We report some preliminary results from a quantitative investigation of the possible astrophysical origins for ^41Ca.

Mineral chemistry mapping and O-isotope study of a compact type A CAI and coagulation modeling bring new information about CAI growth in the solar nebula.

Updated C, N, and O solar wind abundances measured by backside depth-profiling using SIMS and strategies for their absolute calibration are presented.

We present for the first time Na, Al, and Mg fluences in the solar wind (SW) measured in Genesis regime collectors. SW fractionation processes are discussed.

Titanium-isotope anomalies in hibonite grains have been used to investigate nucleosynthetic sources and mixing processes in the early solar system.

To evaluate the disturbance to the Al-Mg system in CAIs we compare our new SIMS data for Allende Type B CAIs with published bulk rock Al-Mg data.

The short-lived radionuclide 41Ca plays an important role in constraining the immediate astrophysical environment and the formation timescale of the nascent solar system due to its extremely short half-life (0.1 Myr). Nearly 20 years ago, the initial ratio of 41Ca/40Ca in the solar system was determined to be (1.41 ± 0.14) × 10–8, primarily based o...

NASA's Genesis space mission returned samples of solar wind collected over ∼2.3 years. We present elemental and isotopic compositions of He, Ne, and Ar analyzed in diamond-like carbon targets from the slow and fast solar wind collectors to investigate isotopic fractionation processes during solar wind formation. The solar wind provides information...

The high ∆17O values in relict olivine phenocrysts in R chondrules (up to 3‰, i.e., higher than OC olivine) contrast with earlier models that held that R-chondrule precursors had OC-chondrule O-isotopic compositions.

We present first results on texture and isotopic compositions of residues produced by cooling Fo-rich materials in vacuum. The results show that it is evaporation that controls the textures and Mg- and Si-isotopic compositions of crystallized phases.

We present preliminary data on the solar wind Mg isotopic composition in Genesis collectors to quantify the isotopic fractionation between solar wind and the Sun’s photosphere.

FUN inclusion Vigarano 1623-5 shows the first unequivocal correlated petrologic and isotopic evidence for volatilization. O-, Si-, and Mg-isotopic compositions reveal that 1623-5 has experienced several evaporation events and an isotopic exchange of O.

Abstract– Paired meteorites Graves Nunatak 06128 and 06129 (GRA) represent an ancient cumulate lithology (4565.9 Ma ± 0.3) containing high abundances of sodic plagioclase. Textures and stable isotope compositions of GRA indicate that superimposed on the igneous lithology is a complex history of subsolidus reequilibration and low-temperature alterat...

We discuss techniques developed to analyze the oxygen-isotopic compositions of Stardust impact crater residues, and we present results of such measurements of simulated impact crater residues of several mineral standards.

In order to deduce the isotopic compositions in the solar nebula of volatile elements, e.g., noble gases, O, and N, from analyses of the solar wind (SW), we must understand the magnitude of mass-dependent fractionation between the SW and the photosphere. With the exception of evaporation effects in CAIs, mass-dependent fractionation of Mg isotopes...

We document the recent reappearance of anadromous sockeye salmon (Oncorhynchus nerka) that were thought to have been extirpated by the construction of hydroelectric dams on the Coquitlam and Alouette rivers in British Columbia, Canada, in 1914 and 1927, respectively. Unexpected downstream migrations of juveniles during experimental water releases i...

All planetary materials sampled thus far vary in their relative abundance of the major isotope of oxygen, (16)O, such that it has not been possible to define a primordial solar system composition. We measured the oxygen isotopic composition of solar wind captured and returned to Earth by NASA's Genesis mission. Our results demonstrate that the Sun...