The Martian Moons eXploration (MMX) mission will study the Martian moons Phobos and Deimos, Mars,... more The Martian Moons eXploration (MMX) mission will study the Martian moons Phobos and Deimos, Mars, and their environments. The mission scenario includes both landing on the surface of Phobos to collect samples and deploying a small rover for in situ observations. Engineering safeties and scientific planning for these operations require appropriate evaluations of the surface environment of Phobos. Thus, the mission team organized the Landing Operation Working Team (LOWT) and Surface Science and Geology Sub-Science Team (SSG-SST), whose view of the Phobos environment is summarized in this paper. While orbital and large-scale characteristics of Phobos are relatively well known, characteristics of the surface regolith, including the particle size-distributions, the packing density, and the mechanical properties, are difficult to constrain. Therefore, we developed several types of simulated soil materials (simulant), such as UTPS-TB (University of Tokyo Phobos Simulant, Tagish Lake based)...
Introduction: Ca, Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) are thought to... more Introduction: Ca, Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) are thought to have formed in a gas of ~solar composition in a hot innermost region of the protoplanetary disk at the birth of the solar system. The presence of these objects in chondrites and 81P/Wild 2 comet suggests CAIs and AOAs were subsequently transported outward from this region and dispersed throughout the disk. The exact mechanism of this transport, however, is not understood: radial transport by disk wind and by disk expansion and turbulent diffusion are being discussed [e.g., 1‒3]. We have recently described abundant relict O-rich olivine grains, most likely related to AOAs, in agglomeratic olivine chondrules and igneous rims around chondrules; both types of objects experienced melting to a very minor degree [4‒7]. In CR chondrules, the abundance of O-rich relict grains is several % [6]. Because chondrules in different chondrite groups formed in different disk regions, the abundances of O-...
Hypervelocity impacts produce unexpected signatures such as glassy coating and hydrated features ... more Hypervelocity impacts produce unexpected signatures such as glassy coating and hydrated features on metal-rich asteroid surfaces.
Chondrules are one of the major components of primitive meteorites. Their sphericity indicates th... more Chondrules are one of the major components of primitive meteorites. Their sphericity indicates they formed as molten fragments or droplets but conditions and mechanisms of chondrule formation remain unknown. A possible scenario is their formation during hypervelocity impacts and ejections. To challenge this idea, we prepared an experiment that reproduces analogous of iron metal-rich chondrules by impact between a glassy silicate projectile and a metallic steel target. The hypervelocity experiment setting allowed an impact velocity of 5 km/s, and was also designed to collect the ejecta. A scanning electron microscopy survey shows that silicate ejecta share several similarities with chondrules. They formed from a population of small melt fragments whose size distribution has the same shape as the size distribution of chondrules, with a shift in size: ejecta are about one order of
Early Solar System planetesimal thermal models predict the heating of the chondritic protolith an... more Early Solar System planetesimal thermal models predict the heating of the chondritic protolith and the preservation of a chondritic crust on differentiated parent bodies. Petrological and geochemical analyses of chondrites have suggested that secondary alteration phases formed at low temperatures (<300 °C) by fluid-rock interaction where reduced and oxidized Vigarano type Carbonaceous (CV) chondrites witness different physicochemical conditions. From a thermodynamical survey of Ca-Fe-rich secondary phases in CV3 chondrites including silica activity (aSiO2), here we show that the classical distinction between reduced and oxidized chondrites is no longer valid and that their Ca-Fe-rich secondary phases formed in similar reduced conditions near the iron-magnetite redox buffer at low aSiO2 (log(aSiO2) <−1) and moderate temperature (210–610 °C). The various lithologies in CV3 chondrites are inferred to be fragments of an asteroid percolated heterogeneously via porous flow of hydrot...
The presence of magmatic magnetites in chondrules implies their formation under impact-generated ... more The presence of magmatic magnetites in chondrules implies their formation under impact-generated oxidizing conditions.
Introduction: Sulfur, the tenth most abundant element in the solar system, is present in primtiti... more Introduction: Sulfur, the tenth most abundant element in the solar system, is present in primtitive chondrite with an average concentration of around 2 wt%. It occurs almost exclusively as stoichiometric iron sulfide troilite (FeS) blebs that are located within or near the edge of chondrules. The origin of these troilite blebs is still a matter of debate. If the FeS phases are primary (i.e., they were present in the chondrule precursors), they would have crystallized from an immiscible sulfide melt during cooling of a chondrule melt [1]. However, experimental studies suggest that troilite should have been vaporized under thermal conditions expected for chondrules formation [2]. Hence, it has been proposed that sulfur would have recondensed as sulfides veeners on the surface of the solidified chondrules [3]. However, the sulfur isotopic composition of putative primary troilite preserved within chondrules and sulfides veeners do not show any measurable isotopic differences contrary to what would be excepted for such a process [4]. Thus, it is generally proposed that sulfur underwent important secondary redistribution in the solar nebula and/or during parent-body processes [3]. However, the origin of sulfides remains poorly constrained despite their importance in understanding the nature, the kinetic and the chronology of the processes that affects chondrules formation and evolution. Here we report a systematic petrographic and mineralogical study of sulfides in type I chondrules of the carbonaceous chondrite Vigarano (CV3) in order to establish the conditions under which they formed. Methods: We surveyed all the type I chondrules in two thin sections of Vigarano (CV3), using Scanning Electron Microscopy (SEM) and Energy Dispersive Xray spectral (EDX). We also acquired multi-elements EDX maps of 25 selected chondrules of all petrological types. Based on the compilation of Mg, Si, Fe, Ni and S maps, we determined the modal abundances of the different silicate phases (olivine, pyroxene & mesostasis) and the metallic phases (Fe-Ni metal and sulfides). Quantitative analyses for the mineralogical composition of chondrules were performed with a CAMECA SX-50 electron microprobe, paying special attention to the sulfur content determination. Results: The vast majority of the type I chondrules we observed present a radial zonation in their mineralogical assemblages with olivines and mesostasis being located in the inner part of the chondrules while the
Introduction: Al-rich (>10 wt% Al 2 O 3) chondrules are compositionally most similar to CAIs and ... more Introduction: Al-rich (>10 wt% Al 2 O 3) chondrules are compositionally most similar to CAIs and can potentially provide a clue for understanding genetic relationship between CAIs and Fe,Mgchondrules. Based on the mineralogical and textural observations, it was previously inferred that Al-rich chondrules in carbonaceous chondrites formed by melting of CAIs largely composed of spinel, anorthite, and diopside, and ferromagnesian precursors compositionally similar to Type I chondrules [1,2]. This model, however, appears to be inconsistent with O-isotopic compositions of Al-rich chondrules from unequilibrated ordinary chondrites (UOCs) Chainpur (LL3.4), Inman (L3.4), Quinyambie (L3.4), and Sharps (H3.4), which on a three-oxygen isotope diagram define a slope of ~0.8, distinct from a slope of ~1 along which most CAIs plot [3]. In order to minimize possible effects of isotope exchange during thermal metamorphism and to test the model of [1,2], we measured in situ O-isotopic compositions of the Al-rich and Fe,Mgchondrules in CR carbonaceous chondrites, which although experienced varying degrees of aqueous alteration, show no evidence for thermal metamorphism [4]. Results: Ferromagnesian Type I chondrules in CRs have porphyritic textures and consist of forsteritic olivine and low-Ca pyroxene phenocrysts and glassy or microcrystalline mesostasis; some chondrules are surrounded by silica-rich igneous rims [5]. Al-rich chondrules in CRs have porphyritic textures and consist of spinel, anorthitic plagioclase, high-Ca and low-Ca pyroxenes, forsteritic olivine and glassy or fine-grained mesostasis composed of silica, anorthitic plagioclase and high-Ca pyroxene [1]. Based on the textures, the Al-rich chondrules can be subdivided into two groups: with and without relict CAI-like regions; the latter were more extensively melted than the former. The Alrich chondrules with relict CAIs have heterogeneous O-isotopic compositions with spinel and ±anorthite enriched in 16 O compared to the phenocrysts of forsterite, low-Ca and high-Ca pyroxene (Fig. 1a). The Alrich chondrules without relict CAIs and most ferromagnesian Type I chondrules have rather similar Oisotopic compositions and are isotopically uniform (Fig. 1b,c). The only exception is chondrule MAC87320 #11 with an olivine grain (possibly relict) enriched in 16 O compared to the other olivine and low-Ca pyroxene grains analyzed. In contrast to O-isotopic Lunar and Planetary Science XXXV (2004) 1389.pdf
Fig. 1. Chemical compositions (in wt%) of melt inclusions and glassy mesostases in Type I chondru... more Fig. 1. Chemical compositions (in wt%) of melt inclusions and glassy mesostases in Type I chondrules from Semarkona and CR carbonaceous chondrites [6, 8-10]. a) CaO vs. SiO2. b) Al2O3 vs. SiO2. c) Al2O3 vs. SiO2 in glasses of two chemically-zoned chondrules from Semarkona and PCA91082 (CR). Representative bulk compositions of Type I chondrules from Semarkona [8,9] are plotted (crosses: PO chondrules; crossed squares: POP and PP chondrules). Black solid lines represent modeled or experimented olivine-and/or low-Ca pyroxene-saturated liquid lines of descent.
Les chondres, sphérules infra-millimétriques composées de minéraux silicatés de haute température... more Les chondres, sphérules infra-millimétriques composées de minéraux silicatés de haute température, sont les constituants majeurs des météorites primitives. Ils présentent d'importantes variabilités texturales et chimiques révélatrices d'une histoire complexe. Cette thèse s'est intéressée à la chronologie de formation des chondres et de leurs précurseurs à deux échelles de temps distinctes aux moyens de deux approches complémentaires : la géochimie isotopique via le chronomètre isotopique à courte période 26Al-26Mg et la pétrologie expérimentale. Le développement au cours de cette thèse d'un protocole analytique innovant de mesure in situ de haute précision par sonde ionique des compositions isotopiques du Mg et Al, a permis de démontrer l'homogénéité de la distribution de l'26Al dans le disque d'accrétion, ce qui présente d'importantes implications sur la chronologie relative et les processus de formation des chondres, mais aussi sur l'origine de ...
Proceedings of the International Astronomical Union, 2012
Space-based and remote sensing observations reveal that regolith – a layer of loose unconsolidate... more Space-based and remote sensing observations reveal that regolith – a layer of loose unconsolidated material – is present on all asteroids, including very small, subkm-sized near- Earth asteroids (NEAs) such as (25143) Itokawa. Classically, regolith is believed to be produced by the ejecta of impact craters produced by small particles hitting asteroid surfaces. Such an explanation works for bodies whose gravity field is strong enough for substantial reaccretion of impact debris, but it fails to account for the ubiquitous presence of regolith also on small asteroids with weaker gravity. Several works have proposed that the thermal fatigue due to a huge number of day/night temperature cycles is a process that contributes to the formation of regolith on the Moon, Mercury, and on the NEA (433) Eros by fracturing boulders and rocks on their surfaces. However, this process lacks a demonstration: in order to study under which conditions rock cracking on NEAs occurs, we calculated typical te...
Space-based [12] and remote sensing observations [4] reveal that regolith-a layer of loose uncons... more Space-based [12] and remote sensing observations [4] reveal that regolith-a layer of loose unconsolidated material-is present on all asteroids, including very small, sub km-sized near-Earth asteroids (NEAs) such as (25143) Itokawa [7].
Changes in the chemical and isotopic composition of the solar nebula with time are reflected in t... more Changes in the chemical and isotopic composition of the solar nebula with time are reflected in the properties of different constituents that are preserved in chondritic meteorites. CR-group carbonaceous chondrites are among the most primitive of all chondrite types and must have preserved solar nebula records largely unchanged. We have analyzed the oxygen and magnesium isotopes in a range of the CR constituents of different formation temperatures and ages, including refractory inclusions and chondrules of various types. The results provide new constraints on the time variation of the oxygen isotopic composition of the inner (<5 AU) solar nebula-the region where refractory inclusions and chondrules most likely formed. A chronology based on the decay of short-lived 26 Al (t 1 = 2 $ 0:73 Myr) indicates that the inner solar nebula gas was 16 O-rich when refractory inclusions formed, but less than 0.8 Myr later, gas in the inner solar nebula became 16 O-poor, and this state persisted at least until CR chondrules formed $1-2 Myr later. We suggest that the inner solar nebula became 16 O-poor because meter-sized icy bodies, which were enriched in 17 O and 18 O as a result of isotopic self-shielding during the ultraviolet photodissociation of CO in the protosolar molecular cloud or protoplanetary disk, agglomerated outside the snow line, drifted rapidly toward the Sun, and evaporated at the snow line. This led to significant enrichment in 16 O-depleted water, which then spread through the inner solar system. Astronomical studies of the spatial and temporal variations of water abundance in protoplanetary disks may clarify these processes.
The Martian Moons eXploration (MMX) mission will study the Martian moons Phobos and Deimos, Mars,... more The Martian Moons eXploration (MMX) mission will study the Martian moons Phobos and Deimos, Mars, and their environments. The mission scenario includes both landing on the surface of Phobos to collect samples and deploying a small rover for in situ observations. Engineering safeties and scientific planning for these operations require appropriate evaluations of the surface environment of Phobos. Thus, the mission team organized the Landing Operation Working Team (LOWT) and Surface Science and Geology Sub-Science Team (SSG-SST), whose view of the Phobos environment is summarized in this paper. While orbital and large-scale characteristics of Phobos are relatively well known, characteristics of the surface regolith, including the particle size-distributions, the packing density, and the mechanical properties, are difficult to constrain. Therefore, we developed several types of simulated soil materials (simulant), such as UTPS-TB (University of Tokyo Phobos Simulant, Tagish Lake based)...
Introduction: Ca, Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) are thought to... more Introduction: Ca, Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) are thought to have formed in a gas of ~solar composition in a hot innermost region of the protoplanetary disk at the birth of the solar system. The presence of these objects in chondrites and 81P/Wild 2 comet suggests CAIs and AOAs were subsequently transported outward from this region and dispersed throughout the disk. The exact mechanism of this transport, however, is not understood: radial transport by disk wind and by disk expansion and turbulent diffusion are being discussed [e.g., 1‒3]. We have recently described abundant relict O-rich olivine grains, most likely related to AOAs, in agglomeratic olivine chondrules and igneous rims around chondrules; both types of objects experienced melting to a very minor degree [4‒7]. In CR chondrules, the abundance of O-rich relict grains is several % [6]. Because chondrules in different chondrite groups formed in different disk regions, the abundances of O-...
Hypervelocity impacts produce unexpected signatures such as glassy coating and hydrated features ... more Hypervelocity impacts produce unexpected signatures such as glassy coating and hydrated features on metal-rich asteroid surfaces.
Chondrules are one of the major components of primitive meteorites. Their sphericity indicates th... more Chondrules are one of the major components of primitive meteorites. Their sphericity indicates they formed as molten fragments or droplets but conditions and mechanisms of chondrule formation remain unknown. A possible scenario is their formation during hypervelocity impacts and ejections. To challenge this idea, we prepared an experiment that reproduces analogous of iron metal-rich chondrules by impact between a glassy silicate projectile and a metallic steel target. The hypervelocity experiment setting allowed an impact velocity of 5 km/s, and was also designed to collect the ejecta. A scanning electron microscopy survey shows that silicate ejecta share several similarities with chondrules. They formed from a population of small melt fragments whose size distribution has the same shape as the size distribution of chondrules, with a shift in size: ejecta are about one order of
Early Solar System planetesimal thermal models predict the heating of the chondritic protolith an... more Early Solar System planetesimal thermal models predict the heating of the chondritic protolith and the preservation of a chondritic crust on differentiated parent bodies. Petrological and geochemical analyses of chondrites have suggested that secondary alteration phases formed at low temperatures (<300 °C) by fluid-rock interaction where reduced and oxidized Vigarano type Carbonaceous (CV) chondrites witness different physicochemical conditions. From a thermodynamical survey of Ca-Fe-rich secondary phases in CV3 chondrites including silica activity (aSiO2), here we show that the classical distinction between reduced and oxidized chondrites is no longer valid and that their Ca-Fe-rich secondary phases formed in similar reduced conditions near the iron-magnetite redox buffer at low aSiO2 (log(aSiO2) <−1) and moderate temperature (210–610 °C). The various lithologies in CV3 chondrites are inferred to be fragments of an asteroid percolated heterogeneously via porous flow of hydrot...
The presence of magmatic magnetites in chondrules implies their formation under impact-generated ... more The presence of magmatic magnetites in chondrules implies their formation under impact-generated oxidizing conditions.
Introduction: Sulfur, the tenth most abundant element in the solar system, is present in primtiti... more Introduction: Sulfur, the tenth most abundant element in the solar system, is present in primtitive chondrite with an average concentration of around 2 wt%. It occurs almost exclusively as stoichiometric iron sulfide troilite (FeS) blebs that are located within or near the edge of chondrules. The origin of these troilite blebs is still a matter of debate. If the FeS phases are primary (i.e., they were present in the chondrule precursors), they would have crystallized from an immiscible sulfide melt during cooling of a chondrule melt [1]. However, experimental studies suggest that troilite should have been vaporized under thermal conditions expected for chondrules formation [2]. Hence, it has been proposed that sulfur would have recondensed as sulfides veeners on the surface of the solidified chondrules [3]. However, the sulfur isotopic composition of putative primary troilite preserved within chondrules and sulfides veeners do not show any measurable isotopic differences contrary to what would be excepted for such a process [4]. Thus, it is generally proposed that sulfur underwent important secondary redistribution in the solar nebula and/or during parent-body processes [3]. However, the origin of sulfides remains poorly constrained despite their importance in understanding the nature, the kinetic and the chronology of the processes that affects chondrules formation and evolution. Here we report a systematic petrographic and mineralogical study of sulfides in type I chondrules of the carbonaceous chondrite Vigarano (CV3) in order to establish the conditions under which they formed. Methods: We surveyed all the type I chondrules in two thin sections of Vigarano (CV3), using Scanning Electron Microscopy (SEM) and Energy Dispersive Xray spectral (EDX). We also acquired multi-elements EDX maps of 25 selected chondrules of all petrological types. Based on the compilation of Mg, Si, Fe, Ni and S maps, we determined the modal abundances of the different silicate phases (olivine, pyroxene & mesostasis) and the metallic phases (Fe-Ni metal and sulfides). Quantitative analyses for the mineralogical composition of chondrules were performed with a CAMECA SX-50 electron microprobe, paying special attention to the sulfur content determination. Results: The vast majority of the type I chondrules we observed present a radial zonation in their mineralogical assemblages with olivines and mesostasis being located in the inner part of the chondrules while the
Introduction: Al-rich (>10 wt% Al 2 O 3) chondrules are compositionally most similar to CAIs and ... more Introduction: Al-rich (>10 wt% Al 2 O 3) chondrules are compositionally most similar to CAIs and can potentially provide a clue for understanding genetic relationship between CAIs and Fe,Mgchondrules. Based on the mineralogical and textural observations, it was previously inferred that Al-rich chondrules in carbonaceous chondrites formed by melting of CAIs largely composed of spinel, anorthite, and diopside, and ferromagnesian precursors compositionally similar to Type I chondrules [1,2]. This model, however, appears to be inconsistent with O-isotopic compositions of Al-rich chondrules from unequilibrated ordinary chondrites (UOCs) Chainpur (LL3.4), Inman (L3.4), Quinyambie (L3.4), and Sharps (H3.4), which on a three-oxygen isotope diagram define a slope of ~0.8, distinct from a slope of ~1 along which most CAIs plot [3]. In order to minimize possible effects of isotope exchange during thermal metamorphism and to test the model of [1,2], we measured in situ O-isotopic compositions of the Al-rich and Fe,Mgchondrules in CR carbonaceous chondrites, which although experienced varying degrees of aqueous alteration, show no evidence for thermal metamorphism [4]. Results: Ferromagnesian Type I chondrules in CRs have porphyritic textures and consist of forsteritic olivine and low-Ca pyroxene phenocrysts and glassy or microcrystalline mesostasis; some chondrules are surrounded by silica-rich igneous rims [5]. Al-rich chondrules in CRs have porphyritic textures and consist of spinel, anorthitic plagioclase, high-Ca and low-Ca pyroxenes, forsteritic olivine and glassy or fine-grained mesostasis composed of silica, anorthitic plagioclase and high-Ca pyroxene [1]. Based on the textures, the Al-rich chondrules can be subdivided into two groups: with and without relict CAI-like regions; the latter were more extensively melted than the former. The Alrich chondrules with relict CAIs have heterogeneous O-isotopic compositions with spinel and ±anorthite enriched in 16 O compared to the phenocrysts of forsterite, low-Ca and high-Ca pyroxene (Fig. 1a). The Alrich chondrules without relict CAIs and most ferromagnesian Type I chondrules have rather similar Oisotopic compositions and are isotopically uniform (Fig. 1b,c). The only exception is chondrule MAC87320 #11 with an olivine grain (possibly relict) enriched in 16 O compared to the other olivine and low-Ca pyroxene grains analyzed. In contrast to O-isotopic Lunar and Planetary Science XXXV (2004) 1389.pdf
Fig. 1. Chemical compositions (in wt%) of melt inclusions and glassy mesostases in Type I chondru... more Fig. 1. Chemical compositions (in wt%) of melt inclusions and glassy mesostases in Type I chondrules from Semarkona and CR carbonaceous chondrites [6, 8-10]. a) CaO vs. SiO2. b) Al2O3 vs. SiO2. c) Al2O3 vs. SiO2 in glasses of two chemically-zoned chondrules from Semarkona and PCA91082 (CR). Representative bulk compositions of Type I chondrules from Semarkona [8,9] are plotted (crosses: PO chondrules; crossed squares: POP and PP chondrules). Black solid lines represent modeled or experimented olivine-and/or low-Ca pyroxene-saturated liquid lines of descent.
Les chondres, sphérules infra-millimétriques composées de minéraux silicatés de haute température... more Les chondres, sphérules infra-millimétriques composées de minéraux silicatés de haute température, sont les constituants majeurs des météorites primitives. Ils présentent d'importantes variabilités texturales et chimiques révélatrices d'une histoire complexe. Cette thèse s'est intéressée à la chronologie de formation des chondres et de leurs précurseurs à deux échelles de temps distinctes aux moyens de deux approches complémentaires : la géochimie isotopique via le chronomètre isotopique à courte période 26Al-26Mg et la pétrologie expérimentale. Le développement au cours de cette thèse d'un protocole analytique innovant de mesure in situ de haute précision par sonde ionique des compositions isotopiques du Mg et Al, a permis de démontrer l'homogénéité de la distribution de l'26Al dans le disque d'accrétion, ce qui présente d'importantes implications sur la chronologie relative et les processus de formation des chondres, mais aussi sur l'origine de ...
Proceedings of the International Astronomical Union, 2012
Space-based and remote sensing observations reveal that regolith – a layer of loose unconsolidate... more Space-based and remote sensing observations reveal that regolith – a layer of loose unconsolidated material – is present on all asteroids, including very small, subkm-sized near- Earth asteroids (NEAs) such as (25143) Itokawa. Classically, regolith is believed to be produced by the ejecta of impact craters produced by small particles hitting asteroid surfaces. Such an explanation works for bodies whose gravity field is strong enough for substantial reaccretion of impact debris, but it fails to account for the ubiquitous presence of regolith also on small asteroids with weaker gravity. Several works have proposed that the thermal fatigue due to a huge number of day/night temperature cycles is a process that contributes to the formation of regolith on the Moon, Mercury, and on the NEA (433) Eros by fracturing boulders and rocks on their surfaces. However, this process lacks a demonstration: in order to study under which conditions rock cracking on NEAs occurs, we calculated typical te...
Space-based [12] and remote sensing observations [4] reveal that regolith-a layer of loose uncons... more Space-based [12] and remote sensing observations [4] reveal that regolith-a layer of loose unconsolidated material-is present on all asteroids, including very small, sub km-sized near-Earth asteroids (NEAs) such as (25143) Itokawa [7].
Changes in the chemical and isotopic composition of the solar nebula with time are reflected in t... more Changes in the chemical and isotopic composition of the solar nebula with time are reflected in the properties of different constituents that are preserved in chondritic meteorites. CR-group carbonaceous chondrites are among the most primitive of all chondrite types and must have preserved solar nebula records largely unchanged. We have analyzed the oxygen and magnesium isotopes in a range of the CR constituents of different formation temperatures and ages, including refractory inclusions and chondrules of various types. The results provide new constraints on the time variation of the oxygen isotopic composition of the inner (<5 AU) solar nebula-the region where refractory inclusions and chondrules most likely formed. A chronology based on the decay of short-lived 26 Al (t 1 = 2 $ 0:73 Myr) indicates that the inner solar nebula gas was 16 O-rich when refractory inclusions formed, but less than 0.8 Myr later, gas in the inner solar nebula became 16 O-poor, and this state persisted at least until CR chondrules formed $1-2 Myr later. We suggest that the inner solar nebula became 16 O-poor because meter-sized icy bodies, which were enriched in 17 O and 18 O as a result of isotopic self-shielding during the ultraviolet photodissociation of CO in the protosolar molecular cloud or protoplanetary disk, agglomerated outside the snow line, drifted rapidly toward the Sun, and evaporated at the snow line. This led to significant enrichment in 16 O-depleted water, which then spread through the inner solar system. Astronomical studies of the spatial and temporal variations of water abundance in protoplanetary disks may clarify these processes.
Uploads
Papers by Guy Libourel