Accretion of water in carbonaceous chondrites: current evidence and implications for the delivery of water to early Earth

Protoplanetary disks are dust-rich structures around young stars. The crystalline and amorphous materials contained within these disks are variably thermally processed and accreted to make bodies of a wide range of sizes and compositions, depending on the heliocentric distance of formation. The chondritic meteorites are fragments of relatively small and undifferentiated bodies, and the minerals that they contain carry chemical signatures providing information about the early environment available for planetesimal formation. A current hot topic of debate is the delivery of volatiles to terrestrial planets, understanding that they were built from planetesimals formed under far more reducing conditions than the primordial carbonaceous chondritic bodies. In this review, we describe significant evidence for the accretion of ices and hydrated minerals in the outer protoplanetary disk. In that distant region highly porous and fragile carbon and water-rich transitional asteroids formed, being the parent bodies of the carbonaceous chondrites (CCs). CCs are undifferentiated meteorites that never melted but experienced other physical processes including thermal and aqueous alteration. Recent evidence indicates that few of them have escaped significant alteration, retaining unique features that can be interpreted as evidence of wet accretion. Some examples of carbonaceous chondrite parent body aqueous alteration will be presented. Finally, atomistic interpretations of the first steps leading to water-mediated alteration during the accretion of CCs are provided and discussed. From these new insights into the water retained in CCs we can decipher the pathways of delivery of volatiles to the terrestrial planets.Comment: 37 pages, 2 Tables, 10 Figures Presented in the International ESAC workshop "Ices in the Solar System" To be published in Space Science Reviews (SPAC-D-18-00036R3

Comparing the reflectivity of ungrouped carbonaceous chondrites with that of short period comets like 2P/Encke

Aims. The existence of asteroid complexes produced by the disruption of these comets suggests that evolved comets could also produce high-strength materials able to survive as meteorites. We chose as an example comet 2P/Encke, one of the largest object of the so-called Taurid complex. We compare the reflectance spectrum of this comet with the laboratory spectra of some Antarctic ungrouped carbonaceous chondrites to investigate whether some of these meteorites could be associated with evolved comets. Methods. We compared the spectral behaviour of 2P/Encke with laboratory spectra of carbonaceous chondrites. Different specimens of the common carbonaceous chondrite groups do not match the overall features and slope of comet 2P/Encke. Trying anomalous carbonaceous chondrites, we found two meteorites, Meteorite Hills 01017 and Grosvenor Mountains 95551, which could be good proxies for the dark materials forming this short-period comet. We hypothesise that these two meteorites could be rare surviving samples, either from the Taurid complex or another compositionally similar body. In any case, it is difficult to get rid of the effects of terrestrial weathering in these Antarctic finds, and further studies are needed. Future sample return from the so-called dormant comets could be also useful to establish a ground truth on the materials forming evolved short-period comets. Results. As a natural outcome, we think that identifying good proxies of 2P/Encke-forming materials might have interesting implications for future sample-return missions to evolved, potentially dormant or extinct comets. To understand the compositional nature of evolved comets is particularly relevant in the context of the future mitigation of impact hazard from these dark and dangerous projectiles.Comment: Accepted for publication in A&A on July 6, 202

The reflectance spectra of CV-CK carbonaceous chondrites from the near-infrared to the visible

Carbonaceous chondrite meteorites are so far the only available samples representing carbon-rich asteroids and in order to allow future comparison with samples returned by missions such as Hayabusa 2 and OSIRIS-Rex, it is important to understand their physical properties. Future characterization of asteroid primitive classes, some of them targeted by sample-return missions, requires a better understanding of their mineralogy, the consequences of the exposure to space weathering, and how both affect the reflectance behaviour of these objects. In this paper, the reflectance spectra of two chemically related carbonaceous chondrites groups, precisely the Vigrano (CVs) and Karoonda (CKs), are measured and compared. The available sample suite includes polished sections exhibiting different petrologic types: from 3 (very low degree of thermal metamorphism) to 5 (high degree of thermal metamorphism). We found that the reflective properties and the comparison with the Cg asteroid reflectance class point towards a common chondritic reservoir from which the CV–CK asteroids collisionally evolved. In that scenario, the CV and CK chondrites could be originated from 221 Eos asteroid family, but because of its collisional disruption, both chondrite groups evolved separately, experiencing different stages of thermal metamorphism, annealing, and space weatheringPeer ReviewedPostprint (author's final draft

Reflectance properties and mineralogy of asteroids by using carbonaceous chondrites

Per tal de comprendre el Sistema Solar en la seva forma actual i la formació dels planetes, els cossos menors juguen un paper clau. La composició d'asteroides i cometes ens proporciona claus sobre el naixement del Sistema Solar i la seva evolució. Els petits cossos no diferenciats contenen els primers materials sòlids del Sistema Solar, formats arran de l'agregació i la fusió del pols primordial. A partir d'aquests primers blocs constitutius es formaren cóssos majors com ara asteroides, cometes i planetes. Els cossos rocosos amb un tamany major a pocs centenars de quilòmetres de diàmetre experimentaren segregació química degut a la diferenciació, però els menors irradiaren la calor interior i mai es van fondre. Els cossos no diferenciats han preservat els materials pristins que formaven el disc protoplanetari. Aquests materials preservats conformen els meteorits no diferenciats. Els meteorits procedint d'aquests objectes, coneguts com a condrites, són mostres dels materials formats al disc protoplanetari al voltant del Sol fa uns 4.600 milions d'anys. Entre aquests, les condrites carbonàcies són les úniques mostres disponibles que representen asteroides carbonacis que són importants per tal de comprendre les seves propietats físiques i per comparar amb les retornades per les missions Hayabusa 2 i OSIRIS-Rex. Aquesta tesi es centra en la composició química, mineralogía i propietats físico-químiques dels cossos menors del Sistema Solar mitjançant mesures al laboratori dels seus meteorits. Diverses tècniques aquí descrites permeten l'estudi de les propietats de les condrites i, d'aquesta manera, obtenir claus sobre les complexes històrias acrecionàries dels seus cossos progenitors. Els canvis mineralògics associats al metamorfisme tèrmic, l'alteració aquosa o als efectes de xoc a condrites són descrits en el context d'indagar en la natura dels seus asteroides pares. A més, s'apliquen tècniques espectroscòpiques com a mètode adient per tal d'associar els meteorits als seus asteroides específics, tot i que una associació inequívoca requerirà completar missiones de retorn de mostres. A la primera part d'aquest treball es comparen els espectres de reflexió de dos grups de condrites carbonàcies químicamente relacionades: CV i CK. Les propietats reflectives d'aquests dos grups de condrites són comparades amb la classe espectral Cg d'asteroides. Donat que els asteroides han estat exposats a impactes des de la seva formació, les seves superficies són cobertes per petites partícules, roques i blocs majors. La missió Hayabusa de JAXA va recolectar partícules del regòlit de l'asteroide 25143 Itokawa. Els estudis al laboratori d'aquestes partícules proporcionen una oportunitat científica donat que les seves propietats físiques poden ser comparades amb aquestes de les condrites que poden ser doncs considerades bons exemples dels materials constitutius dels asteroides potencialment perillosos (PHAs). A la segona part de la tesi es presenten els resultats de l'estudi de les propietats mecàniques de tres d'aquestes partícules fent servir una tècnica acurada anomenada nanoindentació. Finalment també s'estudien les propietats de cossos foscos associats amb cometes evolucionats. En aquest sentit el cometa 2P/Encke és un dels majors objectes de l'anomenat complex de les Tàurides. El seu comportament espectral fa que sigui similar a les condrites carbonàcies prístines però es desconeixia la seva natura real. A aquest treball s'ha trobat un bon ajust espectral entre el cometa i dues condrites carbonàcies sense agrupar, tot permetent fer-nos una idea sobre la composició heterogènia de la superficie d'un cometa de periode curt.Para comprender el Sistema Solar en su forma actual y la formación de los planetas, los cuerpos pequeños juegan un papel clave. La composición de asteroides y cometas nos proporciona claves sobre el nacimiento del sistema solar y su evolución. Los pequeños cuerpos no diferenciados contienen los primeros materiales sólidos del Sistema Solar, formados a partir de la agregación y el fundido del polvo primordial. A partir de estos primeros bloques constitutivos se formaron cuerpos mayores como los asteroides, cometas y planetas. Los cuerpos rocosos con un tamaño mayor a pocos cientos de kilómetros de diámetro experimentaron segregación química debido a la diferenciación, pero los menores irradiaron el calor interior y nunca se fundieron. Los cuerpos no diferenciados han preservado los materiales prístinos que formaban el disco protoplanetario. Estos materiales preservados están alojados en meteoritos no diferenciados. Los meteoritos procedentes de estos objetos, conocidos como condritas, son muestras de materiales formados en el disco protoplanetario alrededor del Sol hace unos 4.600 millones de años. Entre ellos, las condritas carbonáceas son las únicas muestras disponibles que representan asteroides carbonáceos que son importantes para comprender sus propiedades físicas y para comparar con las muestras retornadas por las misiones Hayabusa 2 y OSIRIS-Rex. Esta tesis se centra en la composición química, mineralogía, así como las propiedades físico-químicas de los cuerpos menores del Sistema Solar mediante medidas en el laboratorio de sus meteoritos. Diversas técnicas descritas aquí permiten el estudio de las propiedades de las condritas y, de esta manera, obtener claves sobre las complejas historias acrecionarias de sus cuerpos progenitores. Los cambios mineralógicos asociados al metamorfismo térmico, la alteración acuosa o a los efectos de choque en condritas son descritos en el contexto de indagar en la naturaleza de sus asteroides padres. Además, técnicas espectroscópicas son aplicadas como un método adecuado para asociar los meteoritos a sus asteroides específicos, aunque una asociación inequívoca requerirá completar misiones de retorno de muestras. En la primera parte de este trabajo se comparan los espectros de reflexión de dos grupos de condritas carbonáceas químicamente relacionados: CV y CK. Las propiedades reflectivas de esos dos grupos de condritas son comparados con la clase espectral Cg de asteroides. Dado que los asteroides han sido expuestos a impactos desde su formación sus superficies están cubiertas por pequeñas partículas, rocas y bloques mayores. La misión Hayabusa de JAXA recolectó partículas del regolito del asteroide 25143 Itokawa. Los estudios en el laboratorio de esas partículas proporcionan una oportunidad científica dado que sus propiedades físicas pueden ser comparadas con aquellas de las condritas que pueden ser consideradas buenos ejemplos de los materiales constitutivos de los asteroides potencialmente peligrosos (PHAs). En la segunda parte de la tesis se presentan los resultados del estudio de las propiedades mecánicas de tres de esas partículas usando una técnica precisa denominada nanoindentación. Finalmente también se estudian las propiedades de cuerpos oscuros asociados con cometas evolucionados. En ese sentido el cometa 2P/Encke es uno de los mayores objetos del llamado complejo de las Táuridas. Su comportamiento espectral hace que sea similar a las condritas carbonáceas prístinas, pero se conocía bien poco a su naturaleza real. En este trabajo se ha encontrado un buen ajuste espectral entre el cometa y dos condritas carbonáceas sin agrupar, lo que permite hacernos una idea sobre la composición heterogénea de la superficie de un cometa de periodo corto.To understand the solar system in its current form, and the formation of the planets, small bodies play a key role. The composition of asteroids and comets provides the clues about the birth of the solar system and its evolution. Small undifferentiated bodies contain the first solid materials of the Solar System, formed from the aggregation and melting of primordial dust. From these primordial building blocks much larger bodies such as asteroids, comets and planets were formed. Rocky bodies with a size of few hundreds of kilometers experienced chemical segregation due to differentiation, but the smaller ones irradiated the internal heat and never melted. These undifferentiated bodies have preserved pristine materials that were forming the protoplanetary disk. These materials are hosted by undifferentiated meteorites. The meteorites coming from these objects, known as chondrites, are samples of materials formed in the protoplanetary disk around the Sun about 4,600 million years ago. Among them, the carbonaceous chondrites are the only available samples representing carbonaceous asteroids which are important to understand their physical properties and for future comparison with samples returned by Hayabusa 2 and OSIRIS-Rex missions. This thesis focuses on the chemical composition, mineralogy, as well as the physical and mechanical properties of Solar System small bodies through laboratory measurements of their meteorites. Several techniques described here allow the study of the properties of chondrites, and therefore provide clues about the complex accretionary histories of their parent bodies. The mineralogical changes associated with thermal metamorphism, aqueous alteration, or to the effects of shock in chondrites are described here in the context of getting clues about their possible parent asteroids. Besides, spectroscopic techniques are applied as a suitable method to link the meteorite samples to specific asteroids, although an unambiguous association will require to complete future sample return missions. In the first part of the work, the reflectance spectra of two chemically-related carbonaceous chondrites groups, precisely the CVs and CKs are measured and compared. The reflective properties of these two chondrite groups and the comparison with the Cg asteroid reflectance class supports a common formation scenario. Asteroids have been exposed to impacts since their formation, and as a consequence their surfaces are covered by small particles, pebbles, and boulders. The Japanese JAXA Hayabusa mission collected particles from the regolith of asteroid 25143 Itokawa. Laboratory studies of these particles provide a scientific opportunity as their physical properties can be compared with those characteristic of chondrites that can be considered proxies of the building materials of potentially hazardous asteroids (PHAs). In the second part of the thesis the results from a study of the mechanical properties of three of these particles using a precise technique called nanoindentation are presented. Finally, the properties of dark bodies associated with evolved comets are studied. In that sense, comet 2P/Encke is one of the largest object of the so-called Taurid complex. Its spectral behaviour makes it similar to pristine carbonaceous asteroids, but little was known about its real nature. In this work a good spectral match between this comet and two ungrouped chondrites has been found, allowing us to make a first-guess about the heterogeneous composition of the surface of a short-period comet

Mechanical properties of particles from the surface of asteroid 25143 Itokawa

Aims. Asteroids have been exposed to impacts since their formation, and as a consequence their surfaces are covered by small particles, pebbles, and boulders. The Japanese JAXA/ISAS Hayabusa mission collected micron-sized particles from the regolith of asteroid 25143 Itokawa. The study in terrestrial laboratories of these particles provides a scientific opportunity as their physical properties can be compared with those characteristic of chondritic meteorites that are often considered proxies of the building materials of potentially hazardous asteroids (PHAs). Methods. Here we present the results from a study of the mechanical properties of three of these particles using a precise technique called nanoindentation. The derived results are compared with those obtained via a methodology similar to that used for the Chelyabinsk meteorite. Results. The reduced Young’s modulus values obtained for the Itokawa samples are higher than those measured for the Chelyabinsk chondrite, so these specific particles of asteroid regolith are more compacted than the minerals forming the particular LL chondrite associated with PHAs. This might be a natural consequence of particles surviving long exposure times on the surface of a (near-Earth asteroid) NEA. The Double Asteroid Redirection Test (DART) mission plans to excavate a crater in the surface of the (65803) Didymos satellite. Our results suggest that excavating a crater with a kinetic impactor in an area of significant fine-grained regolith will increase the momentum transfer. As this will facilitate the release of particles carrying target mass in the opposite direction to the movement of the projectile, there is no need to grind up the target during the mechanical excavation phase

Mechanical properties of particles from the surface of asteroid 25143 Itokawa

Aims. Asteroids have been exposed to impacts since their formation, and as a consequence their surfaces are covered by small particles, pebbles, and boulders. The Japanese JAXA/ISAS Hayabusa mission collected micron-sized particles from the regolith of asteroid 25143 Itokawa. The study in terrestrial laboratories of these particles provides a scientific opportunity as their physical properties can be compared with those characteristic of chondritic meteorites that are often considered proxies of the building materials of potentially hazardous asteroids (PHAs). Methods. Here we present the results from a study of the mechanical properties of three of these particles using a precise technique called nanoindentation. The derived results are compared with those obtained via a methodology similar to that used for the Chelyabinsk meteorite. Results. The reduced Young's modulus values obtained for the Itokawa samples are higher than those measured for the Chelyabinsk chondrite, so these specific particles of asteroid regolith are more compacted than the minerals forming the particular LL chondrite associated with PHAs. This might be a natural consequence of particles surviving long exposure times on the surface of a (near-Earth asteroid) NEA. The Double Asteroid Redirection Test (DART) mission plans to excavate a crater in the surface of the (65803) Didymos satellite. Our results suggest that excavating a crater with a kinetic impactor in an area of significant fine-grained regolith will increase the momentum transfer. As this will facilitate the release of particles carrying target mass in the opposite direction to the movement of the projectile, there is no need to grind up the target during the mechanical excavation phase