ABSTRACT Mercury does not have a dense atmosphere whose altitude dependence is described by a sin... more ABSTRACT Mercury does not have a dense atmosphere whose altitude dependence is described by a single scale height. The Ultraviolet Spectrometer (UVS) instrument on Mariner 10 discovered a tenuous exosphere with gaseous species H, He, and O. Since the Mariner 10 flybys, ground-based telescopes have been used to observe the exosphere of Mercury in the Na and K spectroscopic D lines. Calcium has been observed primarily in the polar and anti-sunward exosphere. Radar-bright regions have been discovered at the poles, attributed to volatile deposits (water or sulfur) in permanently shadowed craters. Recently, Mg was discovered during MESSENGER's second flyby of Mercury. Many more species are predicted to exist in Mercury's exosphere, and they are a diagnostic of the surface composition. In many cases, orders-of magnitude differences exist in the predictions of abundances from different models because of our current lack of understanding of Mercury's surface composition and source processes. The small amount of O at the base of the exosphere (n[O] < 4 × 104 particles/cm-3) relative to the surface abundance (~50%) is surprising. This may indicate that the exospheric O is bound in molecules, is inefficiently desorbed, or efficiently escapes. Elements such as Na, Ca, Ar, Ne and S are expected to yield critical information about Mercury's surface. To fully characterize the temporal and spatial variability of Mercury's exosphere, correlated in situ and ground-based observations are essential. Measurements of Na will enable these correlations. Calcium is a refractory element and may be considered a tracer of ion sputtering processes. Both 36Ar and Ne are not expected to be endogenic to Mercury, but implanted by the solar wind. The S content in Mercury's crust and interior is highly diagnostic of the planet's origin.
The release processes induced by ion sputtering and/or micrometeoroids impacts induces erosion of... more The release processes induced by ion sputtering and/or micrometeoroids impacts induces erosion of the Mercury surface. The sputtered neutrals exhibit spectra peaked at low energies (few eV). Nevertheless, a high-energy neutral signal also emerges, due to these release processes. In principle, the directional neutral signal can be detected, providing information on the local surface composition. In this study, we simulate the neutral signal due to ion sputtering below the cusp regions, assuming a highly anisotropic surface composition. The NPA SERENA / ELENA instrument proposed on board the ESA mission BepiColombo is a nadir-pointing 1-D sensor, able to detect neutral atoms, form tens of eV to about 5 keV with a capability of resolving the major species. The ELENA field-of-view (FOV) is ~ 60 degrees, with the FOV plane perpendicular to the MPO orbital plane. Here, we speculate on the possibility of discriminating composition anisotropies by detecting the high-energy portion of the sp...
ABSTRACT Mercury does not have a dense atmosphere whose altitude dependence is described by a sin... more ABSTRACT Mercury does not have a dense atmosphere whose altitude dependence is described by a single scale height. The Ultraviolet Spectrometer (UVS) instrument on Mariner 10 discovered a tenuous exosphere with gaseous species H, He, and O. Since the Mariner 10 flybys, ground-based telescopes have been used to observe the exosphere of Mercury in the Na and K spectroscopic D lines. Calcium has been observed primarily in the polar and anti-sunward exosphere. Radar-bright regions have been discovered at the poles, attributed to volatile deposits (water or sulfur) in permanently shadowed craters. Recently, Mg was discovered during MESSENGER's second flyby of Mercury. Many more species are predicted to exist in Mercury's exosphere, and they are a diagnostic of the surface composition. In many cases, orders-of magnitude differences exist in the predictions of abundances from different models because of our current lack of understanding of Mercury's surface composition and source processes. The small amount of O at the base of the exosphere (n[O] < 4 × 104 particles/cm-3) relative to the surface abundance (~50%) is surprising. This may indicate that the exospheric O is bound in molecules, is inefficiently desorbed, or efficiently escapes. Elements such as Na, Ca, Ar, Ne and S are expected to yield critical information about Mercury's surface. To fully characterize the temporal and spatial variability of Mercury's exosphere, correlated in situ and ground-based observations are essential. Measurements of Na will enable these correlations. Calcium is a refractory element and may be considered a tracer of ion sputtering processes. Both 36Ar and Ne are not expected to be endogenic to Mercury, but implanted by the solar wind. The S content in Mercury's crust and interior is highly diagnostic of the planet's origin.
ABSTRACT GENIE (Ganymede Europa Neutral Imaging Experiment) (energy range 10 eV - 10 keV) is a hi... more ABSTRACT GENIE (Ganymede Europa Neutral Imaging Experiment) (energy range 10 eV - 10 keV) is a high-angular-resolution detector, based on the ToF technique. Its objective is to map the origin sites of the most energetic neutral particles of the icy moons' exospheres, in order to investigate the interaction between the surface and the environment. The investigation of plasma interaction with the Jupiter's moons and the processes responsible for surface space weathering is one of the coolest topics of the proposed Cosmic Vision mission JUICE since it directly relates to energy exchange within the Jupiter's system, to the moon evolution and finally to the habitability in the harsh radiative environment. Icy surfaces of the Jupiter's moons are continuously irradiated by intense ion fluxes of H+, O+ and S+ in the energy range from keV to MeV. These ions are expected to impact the moon icy surface producing relevant and observable effects such as particles release and chemical and structural modifications of the surface. In particular, the plasma impacting onto the surface causes, via ion-sputtering, radiolysis and backscattering processes, release of neutrals that constitute the exospheres. The energy spectrum of this particle population peaks in the eV range with a non-negligible tail up to hundred eVs. The knowledge of the effectiveness of these processes in this environment is important in order to understand the evolution of the moons and their interactions within the Jupiter's system. The detection of neutral atoms above few 10 eVs (LENA) is a way to univocally relate the exosphere to surface features and to monitor instantaneously the effect of plasma precipitation onto the surface. Thus, GENIE is fully complementary to INM spectrometer, devoted to infer exospheric composition and density. Coupled measurements of LENA and gas composition will improve our knowledge in surface release mechanisms. The observation of LENA at different latitudes and longitudes, resulting in a 2D imaging of plasma precipitation, will provide important information on the plasma circulation at the orbits of the moons. Furthermore, a joint measurement of precipitating ions will permit to estimate the efficiency of the release process. Finally, GENIE jointly with an ion-sensor and a mass spectrometer in the JUICE mission will be for the first time an outstanding opportunity to better understand also the magnetosphere-moon coupling within the Jupiter's system. In particular, a comparison between the surface interaction with the intense radiation at Europa and with the plasma shielding by the internal magnetic field at Ganymede, will provide a unique opportunity to investigate the different evolution scenarios of the Jupiter's moons. In this presentation, the science requirements for GENIE, to be proposed for the JUICE mission, are discussed, in view of the possibility of performing LENA measurements at Ganymede, Callisto and Europa.
ABSTRACT Mercury does not have a dense atmosphere whose altitude dependence is described by a sin... more ABSTRACT Mercury does not have a dense atmosphere whose altitude dependence is described by a single scale height. The Ultraviolet Spectrometer (UVS) instrument on Mariner 10 discovered a tenuous exosphere with gaseous species H, He, and O. Since the Mariner 10 flybys, ground-based telescopes have been used to observe the exosphere of Mercury in the Na and K spectroscopic D lines. Calcium has been observed primarily in the polar and anti-sunward exosphere. Radar-bright regions have been discovered at the poles, attributed to volatile deposits (water or sulfur) in permanently shadowed craters. Recently, Mg was discovered during MESSENGER's second flyby of Mercury. Many more species are predicted to exist in Mercury's exosphere, and they are a diagnostic of the surface composition. In many cases, orders-of magnitude differences exist in the predictions of abundances from different models because of our current lack of understanding of Mercury's surface composition and source processes. The small amount of O at the base of the exosphere (n[O] < 4 × 104 particles/cm-3) relative to the surface abundance (~50%) is surprising. This may indicate that the exospheric O is bound in molecules, is inefficiently desorbed, or efficiently escapes. Elements such as Na, Ca, Ar, Ne and S are expected to yield critical information about Mercury's surface. To fully characterize the temporal and spatial variability of Mercury's exosphere, correlated in situ and ground-based observations are essential. Measurements of Na will enable these correlations. Calcium is a refractory element and may be considered a tracer of ion sputtering processes. Both 36Ar and Ne are not expected to be endogenic to Mercury, but implanted by the solar wind. The S content in Mercury's crust and interior is highly diagnostic of the planet's origin.
The release processes induced by ion sputtering and/or micrometeoroids impacts induces erosion of... more The release processes induced by ion sputtering and/or micrometeoroids impacts induces erosion of the Mercury surface. The sputtered neutrals exhibit spectra peaked at low energies (few eV). Nevertheless, a high-energy neutral signal also emerges, due to these release processes. In principle, the directional neutral signal can be detected, providing information on the local surface composition. In this study, we simulate the neutral signal due to ion sputtering below the cusp regions, assuming a highly anisotropic surface composition. The NPA SERENA / ELENA instrument proposed on board the ESA mission BepiColombo is a nadir-pointing 1-D sensor, able to detect neutral atoms, form tens of eV to about 5 keV with a capability of resolving the major species. The ELENA field-of-view (FOV) is ~ 60 degrees, with the FOV plane perpendicular to the MPO orbital plane. Here, we speculate on the possibility of discriminating composition anisotropies by detecting the high-energy portion of the sp...
ABSTRACT Mercury does not have a dense atmosphere whose altitude dependence is described by a sin... more ABSTRACT Mercury does not have a dense atmosphere whose altitude dependence is described by a single scale height. The Ultraviolet Spectrometer (UVS) instrument on Mariner 10 discovered a tenuous exosphere with gaseous species H, He, and O. Since the Mariner 10 flybys, ground-based telescopes have been used to observe the exosphere of Mercury in the Na and K spectroscopic D lines. Calcium has been observed primarily in the polar and anti-sunward exosphere. Radar-bright regions have been discovered at the poles, attributed to volatile deposits (water or sulfur) in permanently shadowed craters. Recently, Mg was discovered during MESSENGER's second flyby of Mercury. Many more species are predicted to exist in Mercury's exosphere, and they are a diagnostic of the surface composition. In many cases, orders-of magnitude differences exist in the predictions of abundances from different models because of our current lack of understanding of Mercury's surface composition and source processes. The small amount of O at the base of the exosphere (n[O] < 4 × 104 particles/cm-3) relative to the surface abundance (~50%) is surprising. This may indicate that the exospheric O is bound in molecules, is inefficiently desorbed, or efficiently escapes. Elements such as Na, Ca, Ar, Ne and S are expected to yield critical information about Mercury's surface. To fully characterize the temporal and spatial variability of Mercury's exosphere, correlated in situ and ground-based observations are essential. Measurements of Na will enable these correlations. Calcium is a refractory element and may be considered a tracer of ion sputtering processes. Both 36Ar and Ne are not expected to be endogenic to Mercury, but implanted by the solar wind. The S content in Mercury's crust and interior is highly diagnostic of the planet's origin.
ABSTRACT GENIE (Ganymede Europa Neutral Imaging Experiment) (energy range 10 eV - 10 keV) is a hi... more ABSTRACT GENIE (Ganymede Europa Neutral Imaging Experiment) (energy range 10 eV - 10 keV) is a high-angular-resolution detector, based on the ToF technique. Its objective is to map the origin sites of the most energetic neutral particles of the icy moons' exospheres, in order to investigate the interaction between the surface and the environment. The investigation of plasma interaction with the Jupiter's moons and the processes responsible for surface space weathering is one of the coolest topics of the proposed Cosmic Vision mission JUICE since it directly relates to energy exchange within the Jupiter's system, to the moon evolution and finally to the habitability in the harsh radiative environment. Icy surfaces of the Jupiter's moons are continuously irradiated by intense ion fluxes of H+, O+ and S+ in the energy range from keV to MeV. These ions are expected to impact the moon icy surface producing relevant and observable effects such as particles release and chemical and structural modifications of the surface. In particular, the plasma impacting onto the surface causes, via ion-sputtering, radiolysis and backscattering processes, release of neutrals that constitute the exospheres. The energy spectrum of this particle population peaks in the eV range with a non-negligible tail up to hundred eVs. The knowledge of the effectiveness of these processes in this environment is important in order to understand the evolution of the moons and their interactions within the Jupiter's system. The detection of neutral atoms above few 10 eVs (LENA) is a way to univocally relate the exosphere to surface features and to monitor instantaneously the effect of plasma precipitation onto the surface. Thus, GENIE is fully complementary to INM spectrometer, devoted to infer exospheric composition and density. Coupled measurements of LENA and gas composition will improve our knowledge in surface release mechanisms. The observation of LENA at different latitudes and longitudes, resulting in a 2D imaging of plasma precipitation, will provide important information on the plasma circulation at the orbits of the moons. Furthermore, a joint measurement of precipitating ions will permit to estimate the efficiency of the release process. Finally, GENIE jointly with an ion-sensor and a mass spectrometer in the JUICE mission will be for the first time an outstanding opportunity to better understand also the magnetosphere-moon coupling within the Jupiter's system. In particular, a comparison between the surface interaction with the intense radiation at Europa and with the plasma shielding by the internal magnetic field at Ganymede, will provide a unique opportunity to investigate the different evolution scenarios of the Jupiter's moons. In this presentation, the science requirements for GENIE, to be proposed for the JUICE mission, are discussed, in view of the possibility of performing LENA measurements at Ganymede, Callisto and Europa.
Uploads
Papers by A. Milillo