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THE IMPORTANCE OF BEING A CRATER: A TOOL IN PLANETARY SURFACE ANALYSIS AND DATATION
Full text linkThis PhD thesis has been realized within the project of STC/SIMBIOSYS, the stereo channel composing the imaging system on board of the BepiColombo mission to Mercury and providing the global mapping in stereo mode of the Hermean surface. As the aim of this work is supporting the definition of the scientific requirements of STC, the impact craters have been recognized as the surface structure to be investigated, being the most important and common landform of any planetary body with a solid surface, but meanwhile far to be yet completely understood.
This thesis addresses to explore the importance of impact crater structure as a tool in investigating a variety of aspects of planetary bodies, whose remote sensing data is the only available information. Earth as well can take advantage from studying such a rarely occurring, complicated and highly dynamic process, as the combining effects of erosion, tectonics and volcanism can hide impact structures.
The first theme turns to impact craters not as an individual entity, but as a population of features on planetary surfaces, in particular Mercury. The cratering records, being the result of a long–repeated meteorite bombardment history, can be used to infer surface age after the application of a chronological model to statistical analysis. The data recently acquired by the MESSENGER mission during its three flybys with this planet were the starting point to study two new basins, i.e. Raditladi and Rachmaninoff. The MPF chronological model has been adopted to derive the crater retention age for these basins, whose impact events turned out to occur well after the LHB, posing some puzzles to the current impactor sources in the inner Solar System. In addition, Rachmaninoff interior plains could be emplaced in a very recent period (360 Ma ago), suggesting a long–lasting volcanism up to recent time, and hence a revision to our current knowledge on the thermal state of the planet is proposed
The second theme of my thesis addresses the investigation of the impact formation process. The current understanding of impact cratering as a whole has come from a suite of experimental, morphological, analytical and numerical studies. However, shocks codes represent one of the only feasible methods for studying impact craters, as they can simulate a large span of conditions beyond the reach of experiments, in addition to analyze the individual effect of any parameters acting during the impact event.
I have used iSALE shock code to simulate two craters, coming from a completely different environment, the Earth and one asteroid, recently observed by a space mission. In the first case, the knowledge of the surrounding area where the structure is located allowed to study in detail the impact crater collapse mechanism that origins a large crater. On the other hand, the good relatively knowledge of the formation of a simple crater allowed to investigate the composition and the structure of the asteroid. In both cases, the numerical modelling of the impact process has demonstrated to be a powerful tool to deepen our comprehension on the Solar System.Questa tesi di dottorato è stata realizzata nell’ambito del progetto di STC/SIMBIOSYS, il canale stereo appartenente al sistema di imaging che a bordo della missione spaziale BepiColombo avrà l’obiettivo di fornire la mappatura globale della superficie di Mercurio in modalità stereo. Poiché lo scopo di questa tesi è di supportare la definizione dei requisiti scientifici della stereo camera, lo studio dei crateri da impatto è stato selezionato come argomento fondamentale. I crateri da impatto sono infatti la più importante e più diffusa morfologia su qualsiasi corpo planetario dotato di una superficie solida, ma allo stesso tempo non ancora completamente compresi.
Questa tesi vuole esplorare l’importanza dei crateri da impatto come tool nell’investigazione di una varietà di aspetti riguardanti i corpi planetari, dei quali si hanno a disposizione solo un numero esiguo di informazioni. Tuttavia, anche nel caso della Terra, per la quale si possiede una grande quantità di dati, lo studio di questo processo altamente dinamico può portare ad una migliore conoscenza del nostro pianeta e delle forze che tutt’ora lo modellano.
Il primo tema di questa tesi riguarda lo studio dei crateri da impatto non come un’entità singola, ma una popolazione di oggetti presenti sulle superfici planetarie, in particolare quella di Mercurio. La craterizzazione su di una superficie è il risultato di una lunga storia di bombardamento meteoritico, e può essere quindi usato per derivare l’età di quella superficie, se si applica un modello cronologico basato sull’analisi statistica dei crateri. I dati recentemente acquisiti dalla missione MESSENGER durante i suoi tre flyby con questo pianeta sono stati l’incipit per lo studio di due nuovi bacini, Raditladi e Rachmaninoff. Si è quindi adottato il modello cronologico MPF per derivare l’età in cui si sono formati questi due bacini. Il risultato di questa analisi è che entrambe le strutture si sono originate in un periodo successivo all’LHB, ponendo interrogativi sulle attuali sorgenti di impattori, considerando la notevole dimensione di queste due strutture d’impatto. Inoltre, le piane interne di Rachmaninoff potrebbero essere molto giovani (360 Ma fa), suggerendo un prolungato vulcanismo, e, a sua volta, una revisione delle nostre attuali conoscenze sullo stato termico di questo pianeta.
Il secondo tema di questa tesi riguarda lo studio del processo di formazione di un impatto. La nostra attuale comprensione di un evento di impatto viene principalmente da studi sperimentali, morfologici, analitici e numerici. Tuttavia, gli shock code rappresentano l’unico procedimento che permette sia di esplorare condizioni non raggiungibili in laboratorio, sia di capire l’influenza di ciascuna variabile durante il processo di impatto.
In questa testi, si è usato iSALE per simulare due crateri, provenienti da due ambienti molto diversi, il nostro pianeta e un asteroide recentemente osservato da una missione spaziale. Nel primo caso, la buona conoscenza della regione dove è collocato il cratere ha permesso di approfondire il meccanismo che sta alla base del collasso di un cratere di grandi dimensioni. Invece, nel secondo caso, era il processo di formazione ad essere meglio conosciuto, dal momento che si trattava di una struttura semplice, e quindi la simulazione numerica è stata finalizzata a investigare la possibile composizione e struttura superficiale di questo asteroide. In entrambi i casi, la modellizzazione numerica del processo di impatto si è dimostrato un capace tool per migliorare la nostra conoscenza del Sistema Solare
A New Chronology for the Moon and Mercury
No full textIn this paper, we present a new method for dating the surface of the Moon, obtained by modeling the incoming flux of impactors and converting it into a size distribution of resulting craters. We compare the results from this model with the standard chronology for the Moon showing their similarities and discrepancies. In particular, we find indications of a nonconstant impactor flux in the last 500 Myr and also discuss the implications of our findings for the Late Heavy Bombardment hypothesis. We also show the potential of our model for accurate dating of other inner solar system bodies, by applying it to Mercury
Omeonga-A possible large impact structure on the Eastern Kasai Province (D.R. Congo)?
No full textThe Omeonga ring structure (D.R. Congo) shows a remarkable drainage pattern encircling an area up to 45 km wide and encompassing a central smoothed relief 20 km wide.
This inner circular ridge is elevated about 70 m above the ring depression corresponding to the bed of the Unia River, which flows between the inner ridge and an outer irregular ridge. Landsat 7 ETM and ASTER DEM show that the structural characteristics resemble those of several wide impact structures known on Earth. Other geological modes of origin that could produce ring structures, such as magmatic activity, salt diapirism, and karst dissolution have been considered. However, after evaluating the regional stratigraphy, the distribution of volcanism, and morphometry, these processes seem to be rather unlikely. If of impact origin, the age of the Omeonga structure can be constrained to the Late Cretaceous-Cenozoic according to the youngest units in which the ring structure was formed
Inflated flows on Daedalia Planum (Mars)?Clues from a comparative analysis with the Payen volcanic complex(Argentina)
No full textInflation is an emplacement process of lava flows, where a thin visco-elastic layer, produced at an early stage, is later inflated by an underlying fluid core. The core remains hot and fluid for extended period of time due to the thermal-shield effect of the surface visco-elastic crust. Plentiful and widespread morphological fingerprints of inflation like tumuli and lava rises are found on the Payen volcanic complex (Argentina), where pahoehoe lava flows extend over the relatively flat surface of the Pampean foreland and reach at least 180 km in length.
The morphology of the Argentinean Payen flows were compared with lava flows on Daedalia Planum (Mars), using Thermal Emission Imaging System (THEMIS), Mars Orbiter Laser Altimeter (MOLA), Mars Orbiter Camera (MOC), Mars Reconnaissance Orbiter (MRO)/High-Resolution Imaging Science Experiment (HiRISE). THEMIS images were used to map the main geological units of Daedalia Planum
and determine their stratigraphic relationships. MOLA data were used to investigate the topographic surface over which the flows propagated and assess the thickness of lava flows. Finally, MOC and MRO/HIRISE images were used to identify inflations fingerprints and assess the cratering age of the
Daedalia Planum’s youngest flow unit which were found to predate the caldera formation on top of the
Arsia Mons. The identification of similar inflation features between the Daedalia Planum and the Payen lava fields suggests that moderate and long lasting effusion rates coupled with very efficient spreading processes could have cyclically occurred in the Arsia Mons volcano during its eruptive history. Consequently the effusion rates and rheological proprieties of Daedalia lava flows,which do not take into account the inflation process, can be overestimated. These findings raise some doubts about the
effusion rates and lava rheological properties calculated on Martian flows and recommends that these should be used with caution if applied on flows not checked with high-resolution images and potentially affected by inflation. Further HiRISE data acquisition will permit additional analysis of the flow surfaces and will allow more accurate estimates of effusion rates and rheological properties of the
lava flows on Mars particularly if this data is acquired under a favorable illumination
Benefits of the Proposed Magia Mission for Lunar Geology
No full textAge of geological units, surface mineralogical composition, volcanism, tectonics and cratering are major keys for unravelling the geodynamic and geological history
of a planet. Thanks to the extensive exploration of the 1960s and 1970s and the compositional mapping of the 1990s missions (Galileo, Clementine and Luna Prospector), the
Moon has a unique geological dataset among the extraterrestrial Solar System bodies. The recent and on-going missions, along with the future plans for lunar exploration, will together acquire an extraordinary amount of data. This should provide a solid basis to meet broad objectives like the constraints on the heterogeneity of Lunar composition and the presence of water deposits, the understanding of volcanic and tectonic evolution as well as more specific issues such as the genetic classification of volcanic domes, origin of the dark halos craters, lava flow emplacement mechanisms, and the kinematics and deformational styles of tectonic structures. The Italian small mission MAGIA (Missione Altimetrica Gravimetrica geochImica lunAre) will be equipped with an integrated context camera and imaging spectrometer, a high resolution camera and a radar altimeter. The spatial and spectral resolution of these instruments will provide data products complementing past and ongoing Lunar mission data, particularly for the polar regions where a full resolution coverage is planned. A general review of some still unanswered questions on lunar surface composition, cold traps, volcanism, tectonics and cratering records is presented here in order to illustrate the potential contribution of MAGIA to these subjects
Numerical modeling of Raditladi and Rachmaninoff basins.
No full textMercury stands among the other ter-restrial planets for the largest population of peak-ring basins. We selected for investigation two struc-tures, Raditladi and Rachmaninoff.
In this work, we will present an update about nu-merical modeling of Raditladi and Rachmaninoff, car-ried out through the iSALE shock code. In addition, we will discuss the comparison between modeling and MESSENGER observations, in order to shed light on the primary impactor source of these basins. In particu-lar, we will focus on their differences, and the possible mechanisms or crust-mantle properties that could have led to such a diversification between two similar struc-tures
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