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BepiColombo has a larger and in many ways more capable suite of instrumentsrelevant for determination of the topographic, physical, chemical and mineralogical proper-ties of Mercury’s surface than the suite carried by NASA’s MESSENGER spacecraft. More-over, BepiColombo’s data rate is substantially higher. This equips it to confirm, elaborateupon, and go beyond many of MESSENGER’s remarkable achievements. Furthermore, thegeometry of BepiColombo’s orbital science campaign, beginning in 2026, will enable itto make uniformly resolved observations of both northern and southern hemispheres. Thiswill offer more detailed and complete imaging and topographic mapping, element mappingwith better sensitivity and improved spatial resolution, and totally new mineralogical map-ping.We discuss MESSENGER data in the context of preparing for BepiColombo, and de-scribe the contributions that we expect BepiColombo to make towards increased knowledgeand understanding of Mercury’s surface and its composition. Much current work, includinganalysis of analogue materials, is directed towards better preparing ourselves to understandwhat BepiColombo might reveal. Some of MESSENGER’s more remarkable observationswere obtained under unique or extreme conditions. BepiColombo should be able to confirmthe validity of these observations and reveal the extent to which they are representative ofthe planet as a whole. It will also make new observations to clarify geological processesgoverning and reflecting crustal origin and evolution.We anticipate that the insights gained into Mercury’s geological history and its currentspace weathering environment will enable us to better understand the relationships of surfacechemistry, morphologies and structures with the composition of crustal types, including thenature and mobility of volatile species. This will enable estimation of the composition of the mantle from which the crust was derived, and lead to tighter constraints on models forMercury’s origin including the nature and original heliocentric distance of the material fromwhich it formed.

Although close to the Sun, Mercury has a unique surface, poorer in iron than the surface of the Moon, but surprisingly rich in volatile elements. These essential discoveries of the MESSENGER mission have raised questions that the BepiColombo mission (ESA/JAXA) will try to answer, thanks in particular to the SIMBIO-SYS instrument, which will provide spectral images of the Mercury surface with a spatial resolution 10 to 100 times higher than that achieved by MESSENGER. Among these fundamental questions is the accurate chemical and mineralogical composition of Mercury. My thesis adresses the problem through a multidisciplinary approach. A first angle consists in using the data provided by MESSENGER to map in color the Shakespeare quadrangle. My work has made it possible to define 1) spectral units of the quadrangle associated with very precise values of various spectral parameters, and 2) regions of interest to be analyzed and characterized notably by the VIHI hyperspectral imager (0.4-2.0 μm), one of the channels of SIMBIO-SYS. The second angle consists of laboratory experiments : heating, cooling and irradiation of possible mineralogical analogues of Mercury’s surface. The aim is to anticipate the arrival of BepiColombo and to know the effects of these alterations on the spectral properties of the minerals. Results obtained from spectroscopic measurements of hermean mineral analogues subjected to Mercury surface conditions have revealed clear variations in their spectral properties (e.g. position and shape of absorption bands).; Bien que proche du Soleil, Mercure possède une surface unique, plus pauvre en fer que la surface de la Lune, mais étonnament riche en éléments volatils. Ces découvertes essentielles de la mission MESSENGER ont soulevé des questions auxquelles tentera de répondre la mission BepiColombo (ESA/JAXA) grâce notamment à l’instrument SIMBIO-SYS qui fournira des images spectrales de la surface de Mercure avec une résolution spatiale 10 à 100 fois plus élevée que celle atteinte par MESSENGER. Parmi ces questions fondamentales figure la composition chimique et minéralogique précise de Mercure. Ma thèse aborde la problématique par une approche pluridisciplinaire. Un premier angle consiste en l’exploitation des données fournies par MESSENGER en cartographiant en couleurs le quadrangle Shakespeare. Mes travaux ont notamment permis de définir 1) des unités spectrales du quadrangle associées à des valeurs bien précises de divers paramètres spectraux, et 2) des régions d’intérêt à analyser et caractériser notamment par le spectro-imageur VIHI (0,4-2,0 μm), une des voies de SIMBIO-SYS. Le deuxième angle consiste en des expériences de laboratoire : chauffage, refroidissement et irradiation d’analogues minéralogiques possibles de la surface de Mercure. Le but est d’anticiper l’arrivée de BepiColombo et de savoir quels sont les effets de ces altérations sur les propriétés spectrales de ces minéraux. Les résultats obtenus de mesures spectroscopiques d’analogues de minéraux herméens soumis aux conditions de la surface de Mercure ont permis de mettre en évidence des variations claires de leurs propriétés spectrales (e.g. position et forme de bandes d’absorption).

International audience

International audience; We present for the first time the effects of both heating and swift heavy ion irradiation on selected minerals (plagioclase and olivine) and volcanic glasses which could be expected on the surface of Mercury. Clear spectral changes are observed for both alterations. This could have strong implications for the future observations of SIMBIO-SYS and MERTIS, two instruments onboard the BepiColombo mission.

International audience; The study of Venus’ cloud layers is important in or-der to understand the structure, radiative balance anddynamics of the Venusian atmosphere. Polarizationmeasurements have given important constraints for thedetermination of the constituents of the clouds andhaze.From ground based observations, Hansen andHovenier[3], using a radiative transfer model includ-ing polarization, found that the main cloud layers be-tween 50 and 70 km consist of r ∼ 1 μm radius spher-ical droplets of a H SO -H O solution.In the early 1980s, Kawabata[4] used the polarization data from the OCPP instrument on the spacecraft Pioneer Venus to constrain the properties of the overlying haze. They found that the haze layer is composed of smaller parti- cles with r ∼ 0.25 μm and similar refractive indices.Our work reproduces the method used by Hansen and Kawabata[3, 4]. We applied a radiative transfer model with polarization on the polarization data of the SPICAV-IR instrument on-board ESA’s Venus Ex- press. Our aim is to better constrain haze and cloud particles at the top of Venus’s clouds, as well as their spatial and temporal variability.

BepiColombo has a larger and in many ways more capable suite of instrumentsrelevant for determination of the topographic, physical, chemical and mineralogical proper-ties of Mercury’s surface than the suite carried by NASA’s MESSENGER spacecraft. More-over, BepiColombo’s data rate is substantially higher. This equips it to confirm, elaborateupon, and go beyond many of MESSENGER’s remarkable achievements. Furthermore, thegeometry of BepiColombo’s orbital science campaign, beginning in 2026, will enable itto make uniformly resolved observations of both northern and southern hemispheres. Thiswill offer more detailed and complete imaging and topographic mapping, element mappingwith better sensitivity and improved spatial resolution, and totally new mineralogical map-ping.We discuss MESSENGER data in the context of preparing for BepiColombo, and de-scribe the contributions that we expect BepiColombo to make towards increased knowledgeand understanding of Mercury’s surface and its composition. Much current work, includinganalysis of analogue materials, is directed towards better preparing ourselves to understandwhat BepiColombo might reveal. Some of MESSENGER’s more remarkable observationswere obtained under unique or extreme conditions. BepiColombo should be able to confirmthe validity of these observations and reveal the extent to which they are representative ofthe planet as a whole. It will also make new observations to clarify geological processesgoverning and reflecting crustal origin and evolution.We anticipate that the insights gained into Mercury’s geological history and its currentspace weathering environment will enable us to better understand the relationships of surfacechemistry, morphologies and structures with the composition of crustal types, including thenature and mobility of volatile species. This will enable estimation of the composition of the mantle from which the crust was derived, and lead to tighter constraints on models forMercury’s origin including the nature and original heliocentric distance of the material fromwhich it formed.