A new chronology for the Moon and Mercury

In 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 non-constant 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.Comment: 27 pages, 13 figures, 1 table; accepted by A

Mercury's geochronology revised by applying Model Production Functions to Mariner 10 data: geological implications

Model Production Function chronology uses dynamic models of the Main Belt Asteroids (MBAs) and Near Earth Objects (NEOs) to derive the impactor flux to a target body. This is converted into the crater size-frequency-distribution for a specific planetary surface, and calibrated using the radiometric ages of different regions of the Moon's surface. This new approach has been applied to the crater counts on Mariner 10 images of the highlands and of several large impact basins on Mercury. MPF estimates for the plains show younger ages than those of previous chronologies. Assuming a variable uppermost layering of the Hermean crust, the age of the Caloris interior plains may be as young as 3.59 Ga, in agreement with MESSENGER results that imply that long-term volcanism overcame contractional tectonics. The MPF chronology also suggests a variable projectile flux through time, coherent with the MBAs for ancient periods and then gradually comparable also to the NEOs.Comment: Accepted by Journal Geophysical Research Letter

Observing Mercury: from Galileo to the stereo camera on the BepiColombo mission

AbstractAfter having observed the planets from his house in Padova using his telescope, in January 1611 Galileo wrote to Giuliano de Medici that Venus is moving around the Sun as Mercury. Forty years ago, Giuseppe Colombo, professor of Celestial Mechanics in Padova, made a decisive step to clarify the rotational period of Mercury. Today, scientists and engineers of the Astronomical Observatory of Padova and of the University of Padova, reunited in the Center for Space Studies and Activities (CISAS) named after Giuseppe Colombo, are busy to realize a stereo camera (STC) that will be on board the European (ESA) and Japanese (JAXA) space mission BepiColombo, devoted to the observation and exploration of the innermost planet. This paper will describe the stereo camera, which is one of the channels of the SIMBIOSYS instrument, aiming to produce the global mapping of the surface with 3D images

A New Orbiting Deployable System for Small Satellite Observations for Ecology and Earth Observation

In this paper, we present several study cases focused on marine, oceanographic, and atmospheric environments, which would greatly benefit from the use of a deployable system for small satellite observations. As opposed to the large standard ones, small satellites have become an effective and affordable alternative access to space, owing to their lower costs, innovative design and technology, and higher revisiting times, when launched in a constellation configuration. One of the biggest challenges is created by the small satellite instrumentation working in the visible (VIS), infrared (IR), and microwave (MW) spectral ranges, for which the resolution of the acquired data depends on the physical dimension of the telescope and the antenna collecting the signal. In this respect, a deployable payload, fitting the limited size and mass imposed by the small satellite architecture, once unfolded in space, can reach performances similar to those of larger satellites. In this study, we show how ecology and Earth Observations can benefit from data acquired by small satellites, and how they can be further improved thanks to deployable payloads. We focus on DORA—Deployable Optics for Remote sensing Applications—in the VIS to TIR spectral range, and on a planned application in the MW spectral range, and we carry out a radiometric analysis to verify its performances for Earth Observation studies

Effects of Impact and Target Parameters on the Results of a Kinetic Impactor: Predictions for the Double Asteroid Redirection Test (DART) Mission

The Double Asteroid Redirection Test (DART) spacecraft will impact into the asteroid Dimorphos on 2022 September 26 as a test of the kinetic impactor technique for planetary defense. The efficiency of the deflection following a kinetic impactor can be represented using the momentum enhancement factor, β, which is dependent on factors such as impact geometry and the specific target material properties. Currently, very little is known about Dimorphos and its material properties, which introduces uncertainty in the results of the deflection efficiency observables, including crater formation, ejecta distribution, and β. The DART Impact Modeling Working Group (IWG) is responsible for using impact simulations to better understand the results of the DART impact. Pre-impact simulation studies also provide considerable insight into how different properties and impact scenarios affect momentum enhancement following a kinetic impact. This insight provides a basis for predicting the effects of the DART impact and the first understanding of how to interpret results following the encounter. Following the DART impact, the knowledge gained from these studies will inform the initial simulations that will recreate the impact conditions, including providing estimates for potential material properties of Dimorphos and β resulting from DART’s impact. This paper summarizes, at a high level, what has been learned from the IWG simulations and experiments in preparation for the DART impact. While unknown, estimates for reasonable potential material properties of Dimorphos provide predictions for β of 1–5, depending on end-member cases in the strength regime

THE IMPORTANCE OF BEING A CRATER: A TOOL IN PLANETARY SURFACE ANALYSIS AND DATATION

This 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

Omeonga-A possible large impact structure on the Eastern Kasai Province (D.R. Congo)?

The 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