ELENA instrument science and testing: validation with particle beam

Understanding of particle emission processes from the Mercury surface is one of the major objectives of ELENAinstrument in the SERENA experiment on board of the BepiColombo mission. In particular the Ion-Sputteringprocess resulting from charged and energetic particles impacting on the surface can be investigated detectingthe low energetic neutral particles escaping from the planet. The possibility to identify the Ion-Sputtering signaltogether with back-scattered particles and neutrals generated by charge exchange is strictly linked with the newtechnology capability to measure low energetic neutral atoms. This goal can be addressed thanks to a new&oldapproach for the neutral atoms measurement: a well known Time of Flight system enhanced with a new kind ofStart section able to define the start time of the entrance in the ToF path without interacting with the particles anddirectly follow to the Stop detector. The Start section is a shutter composed by two membranes with nanometricslits realized in a large area (1cm2) and oscillating at several frequencies to open and close the entrance of ToFsection. This system is never used before in space mission.The IFSI-INAF Ion beam facility in Rome is devoted to the ELENA testing. The crucial point of the shutteringsystem interaction with particle beam is investigated. The first results demonstrate the good functionality of thiskind of system: capability of the shutter to Open and Close the entrance respect to an ion beam is tested with aMCP stop detector. In this poster we present the IFSI activity in the frame of ELENA science requirement togetherwith the experimental activity devoted to instrument verification

Analytical model of Europa's O2 exosphere

The origin of the exosphere of Europa is its water ice surface. The existing exosphere models, assuming either a collisionless environment (simple Monte Carlo techniques) or a kinetic approach (Direct Monte Carlo Method) both predict that the major constituent of the exosphere is molecular oxygen. Specifically, O2 is generated at the surface through radiolysis and chemical interactions of the water dissociation products. The non-escaping O2 molecules circulate around the moon impacting the surface several times, due to their long lifetime and due to their non- sticking, suffering thermalization to the surface temperature after each impact. In fact, the HST observations of the O emission lines proved the presence of an asymmetric atomic Oxygen distribution, related to a thin asymmetric molecular Oxygen atmosphere. The existing Monte Carlo models are not easily applicable as input of simulations devoted to the study of the plasma interactions with the moon. On the other hand, the simple exponential density profiles cannot well depict the higher temperature/higher altitudes component originating by radiolysis. It would thus be important to have a suitable and user-friendly model able to describe the major exospheric characteristics to use as a tool. This study presents an analytical 3D model that is able to describe the molecular Oxygen exosphere by reproducing the two-component profiles and the asymmetries due to diverse configurations among Europa, Jupiter and the Sun. This model is obtained by a non-linear fit procedure of the EGEON Monte Carlo model (Plainaki et al. 2013) to a Chamberlain density profile. Different parameters of the model are able to describe various exosphere properties thus allowing a detailed investigation of the exospheric characteristics. As an example a discussion on the exospheric temperatures in different configurations and space regions is given

The H2O and O2 exospheres of Ganymede: The result of a complex interaction between the jovian magnetospheric ions and the icy moon

The H2O and O2 exospheres of Jupiter's moon Ganymede are simulated through the application of a 3D Monte Carlo modeling technique that takes into consideration the combined effect on the exosphere generation of the main surface release processes (i.e. sputtering, sublimation and radiolysis) and the surface precipitation of the energetic ions of Jupiter's magnetosphere. In order to model the magnetospheric ion precipitation to Ganymede's surface, we used as an input the electric and magnetic fields from the global MHD model of Ganymede's magnetosphere (Jia, X., Walker, R.J., Kivelson, M.G., Khurana, K.K., Linker, J.A. [2009]. J. Geophys. Res. 114, A09209). The exospheric model described in this paper is based on EGEON, a single-particle Monte Carlo model already applied for a Galilean satellite (Plainaki, C., Milillo, A., Mura, A., Orsini, S., Cassidy, T. [2010]. Icarus 210, 385-395; Plainaki, C., Milillo, A., Mura, A., Orsini, S., Massetti, S., Cassidy, T. [2012]. Icarus 218 (2), 956-966; Plainaki, C., Milillo, A., Mura, A., Orsini, S., Saur [2013]. Planet. Space Sci. 88, 42-52); nevertheless, significant modifications have been implemented in the current work in order to include the effect on the exosphere generation of the ion precipitation geometry determined strongly by Ganymede's intrinsic magnetic field (Kivelson, M.G. et al. [1996]. Nature 384, 537-541). The current simulation refers to a specific configuration between Jupiter, Ganymede and the Sun in which the Galilean moon is located close to the center of Jupiter's Plasma Sheet (JPS) with its leading hemisphere illuminated. Our results are summarized as follows: (a) at small altitudes above the moon's subsolar point the main contribution to the neutral environment comes from sublimated H2O; (b) plasma precipitation occurs in a region related to the open-closed magnetic field lines boundary and its extent depends on the assumption used to mimic the plasma mirroring in Jupiter's magnetosphere; (c) the spatial distribution of the directly sputtered-H2O molecules exhibits a close correspondence with the plasma precipitation region and extends at high altitudes, being, therefore, well differentiated from the sublimated water; (d) the O2 exosphere comprises two different regions: the first one is an homogeneous, relatively dense, close to the surface thermal-O2 region (extending to some 100s of km above the surface) whereas the second one is less homogeneous and consists of more energetic O2 molecules sputtered directly from the surface after water-dissociation by ions has taken place; the spatial distribution of the energetic surface-released O2 molecules depends both on the impacting plasma properties and the moon's surface temperature distribution (that determine the actual efficiency of the radiolysis process)

Investigation of the possible effects of comet Encke's meteoroid stream on the Ca exosphere of Mercury

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) observations of the seasonal variability of Mercury's Ca exosphere are consistent with the general idea that the Ca atoms originate from the bombardment of the surface by particles from comet 2P/Encke. The generating mechanism is believed to be a combination of different processes including the release of atomic and molecular surface particles and the photodissociation of exospheric molecules. Considering different generation and loss mechanisms, we perform simulations with a 3-D Monte Carlo model based on the exosphere generation model by Mura et al. (2009). We present for the first time the 3-D spatial distribution of the CaO and Ca exospheres generated through the process of micrometeoroid impact vaporization, and we show that the morphology of the latter is consistent with the available MESSENGER/Mercury Atmospheric and Surface Composition Spectrometer observations. The results presented in this paper can be useful in the exosphere observations planning for BepiColombo, the upcoming European Space Agency-Japanese Aerospace Exploration Agency mission to Mercury

Exospheric Na distributions along the Mercury orbit with the THEMIS telescope

Abstract The Na exosphere of Mercury is characterized by the variability of the emission lines intensity and of its distribution in time scales from less than one hour to seasonal variations. While the faster variations, accounting for about 10–20% of fluctuations are probably linked to the planetary response to solar wind and Interplanetary Magnetic Field variability, the seasonal variations (up to about 80%) should be explained by complex mechanisms involving different surface release processes, loss, source and migrations of the exospheric Na atoms. Eventually, a Na annual cycle can be identified. In the past, ground-based observations and equatorial density from MESSENGER data have been analyzed. In this study, for a more extensive investigation of the exospheric Na features, we have studied the local time and latitudinal distributions of the exospheric Na column density as a function of the True Anomaly Angle (TAA) of Mercury by means of the extended dataset of images, collected from 2009 to 2013, by the THEMIS solar telescope. Our results show that the THEMIS images, in agreement with previous results, registered a strong general increase in sodium abundance at aphelion and a dawn ward emission predominance with respect to dusk ward and subsolar region between 90° and 150° TAA. This behavior can be explained by desorption of a sodium surface reservoir consisting of sodium that is pushed anti-sunward and condenses preferentially in the coldest regions. Our analyses show s a predominance of subsolar line-of-sight column density along the rest of Mercury's orbit. An unexpected relationship between Northward or Southward peak emission and both TAA and local time is also shown by our analysis. This result seems to contradict previous results obtained from different data sets and it is not easily explained, thus it requires further investigations

The H2O and O2 exospheres of Jupiter's moon Ganymede

A simulation of the H_2O and O_2 exospheres of Jupiter' moon Ganymede, through the application of a 3D Monte Carlo modeling technique, is presented. Our model takes into consideration the combined effect on the exosphere generation of the main surface release processes (i.e. sputtering, sublimation and radiolysis) and the surface precipitation of the energetic ions of Jupiter's magnetosphere constrained strongly by Ganymede's intrinsic magnetic field. In order to model the magnetospheric ion precipitation to Ganymede's surface, we used as an input the electric and magnetic fields from the global MHD model of Ganymede's magnetosphere (Jia et al., 2009). The exospheric model described in this paper is based on EGEON, a single-particle Monte Carlo model already applied for a Galilean satellite \citep{PC10,PC12,PC13}. We find that at small altitudes above the moon.s subsolar point the main contribution to the neutral environment comes from sublimated H_2O whereas the spatial distribution of the directly sputtered-H_2O molecules exhibits a close correspondence with the plasma precipitation region and extends at high altitudes, being, therefore, well differentiated from the sublimated water. Moreover, we find that the O_2 exosphere comprises two different regions: the first one is an homogeneous, relatively dense, thermal-O_2 region extending to some 100s of km above the surface, whereas the second one is less homogeneous and consists of more energetic O_2 molecules sputtered directly from the surface after water-dissociation by ions has taken place; the spatial distribution of the energetic surface-released O_2 molecules depends both on the impacting plasma properties and the moon's surface temperature distribution

Solar perturbations transits in Mercury exosphere

The link existing between the dayside Na exospheric patterns of Mercury and the solar wind-magnetosphere-surface interactions is investigated thanks to the synergy of Earth-based observations with the THEMIS solar telescope and the in-situ measurements of the Interplanetary Magnetic Field (IMF) and proton fluxes at the magnetic cusp regions by MESSENGER. Frequently, two-peak patterns of variable intensity are observed, located at high latitudes in both hemispheres. Occasionally, Na signal is instead diffused above the sub-solar region. In a special case, the Na signal is diffused above the subsolar region, when the MESSENGER data detect the transit of two Coronal Mass Ejections (CMEs). Na emission patterns results to be clearly related to the solar wind conditions at Mercury. Hence, the Na exospheric patterns, observed from ground, could be considered as a natural monitor of solar disturbances when transiting near Mercury

SWEATERS Performance Test Plan

Scope of this document is to provide the Performance Test Plan for the prototype of the Space WEATher Ena Radiation Sensors, namely SWEATERS

Single ELENA shutter membrane UV test Plan at IFN in Padova

In the framework of the WP 2500 of the SERENA E1 contract phase ( BepiColombo science activities), we plan to continue with some ground calibration tests of the ELENA FS. In this document we described the UV test that we want to perform to improve the uncertainty of the UV shatter membrane transparency measurements collected till now. For this test we will not use all the ELENA box but only a single membrane of the shutter illuminated with Lyman-α source