Imperial College London


Faculty of Natural SciencesDepartment of Physics

Professor in Planetary Science



m.galand Website




Huxley BuildingSouth Kensington Campus





Publication Type

131 results found

Carnielli G, Galand M, Leblanc F, Modolo R, Beth A, Jia Xet al., 2020, Simulations of ion sputtering at Ganymede, Icarus, Vol: 351, Pages: 1-11, ISSN: 0019-1035

Ganymede's surface is subject to constant bombardment by Jovian magnetospheric and Ganymede's ionospheric ions. These populations sputter the surface and contribute to the replenishment of the moon's exosphere.Thus far, estimates for sputtering on the moon's surface have included only the contribution from Jovian ions. In this work, we have used our recent model of Ganymede's ionosphere Carnielli et al., 2019 to evaluate the contribution of ionospheric ions for the first time. In addition, we have made new estimates for the contribution from Jovian ions, including both thermal and energetic components.For Jovian ions, we find a total sputtering rate of 2.2 × 1027 s−1, typically an order of magnitude higher compared to previous estimates. For ionospheric ions, produced through photo- and electron-impact ionization, we find values in the range 2.7 × 1026–5.2 × 1027 s−1 when the moon is located above the Jovian plasma sheet. Hence, Ganymede's ionospheric ions provide a contribution of at least 10% to the sputtering rate, and under certain conditions they dominate the process. This finding indicates that the ionospheric population is an important source to consider in the context of exospheric models.

Journal article

Galand M, Feldman PD, Bockelee-Morvan D, Biver N, Cheng Y-C, Rinaldi G, Rubin M, Altwegg K, Deca J, Beth A, Stephenson P, Heritier K, Henri P, Parker JW, Carr C, Eriksson AI, Burch Jet al., 2020, Far-ultraviolet aurora identified at comet 67P/ Churyumov-Gerasimenko, Nature Astronomy, ISSN: 2397-3366

Journal article

Beth A, Altwegg K, Balsiger H, Berthelier J-J, Combi MR, De Keyser J, Fiethe B, Fuselier SA, Galand M, Gombosi TI, Rubin M, Sémon Tet al., 2020, ROSINA ion zoo at Comet 67P, Astronomy & Astrophysics, ISSN: 0004-6361

Journal article

Madanian H, Burch JL, Eriksson AI, Cravens TE, Galand M, Vigren E, Goldstein R, Nemeth Z, Mokashi P, Richter I, Rubin Met al., 2020, Electron dynamics near diamagnetic regions of comet 67P/Churyumov- Gerasimenko, Planetary and Space Science, Vol: 187, ISSN: 0032-0633

The Rosetta spacecraft detected transient and sporadic diamagnetic regions around comet 67P/Churyumov-Gerasimenko. In this paper we present a statistical analysis of bulk and suprathermal electron dynamics, as well as a case study of suprathermal electron pitch angle distributions (PADs) near a diamagnetic region. Bulk electron densities are correlated with the local neutral density and we find a distinct enhancement in electron densities measured over the southern latitudes of the comet. Flux of suprathermal electrons with energies between tens of eV to a couple of hundred eV decreases each time the spacecraft enters a diamagnetic region. We propose a mechanism in which this reduction can be explained by solar wind electrons that are tied to the magnetic field and after having been transported adiabatically in a decaying magnetic field environment, have limited access to the diamagnetic regions. Our analysis shows that suprathermal electron PADs evolve from an almost isotropic outside the diamagnetic cavity to a field-aligned distribution near the boundary. Electron transport becomes chaotic and non-adiabatic when electron gyroradius becomes comparable to the size of the magnetic field line curvature, which determines the upper energy limit of the flux variation. This study is based on Rosetta observations at around 200 ​km cometocentric distance when the comet was at 1.24 AU from the Sun and during the southern summer cometary season.

Journal article

Carnielli G, Galand M, Leblanc F, Modolo R, Beth A, Jia Xet al., 2020, Constraining Ganymede's neutral and plasma environments through simulations of its ionosphere and Galileo observations, Icarus, Vol: 343, Pages: 1-11, ISSN: 0019-1035

Ganymede's neutral and plasma environments are poorly constrained by observations. Carnielli et al. (2019) developed the first 3D ionospheric model aimed at understanding the dynamics of the present ion species and at quantifying the presence of each component in the moon's magnetosphere. The model outputs were compared with Galileo measurements of the ion energy flux, ion bulk velocity and electron number density made during the G2 flyby. A good agreement was found in terms of ion energy distribution and bulk velocity, but not in terms of electron number density. In this work, we present some improvements to our model Carnielli et al. (2019) and quantitatively address the possible sources of the discrepancy found in the electron number density between the Galileo observations and our ionospheric model. We have improved the ion model by developing a collision scheme to simulate the charge-exchange interaction between the exosphere and the ionosphere. We have simulated the energetic component of the O$_2$ population, which is missing in the exospheric model of Leblanc et al. (2017) and added it to the original distribution, hence improving its description at high altitudes. These improvements are found to be insufficient to explain the discrepancy in the electron number density. We provide arguments that the input O$_2$ exosphere is underestimated and that the plasma production acts asymmetrically between the Jovian and anti-Jovian hemispheres. In particular, we estimate that the O$_2$ column density should be greater than $10^{15}$~cm$^{-2}$, i.e., higher than previously derived upper limits (and a factor 10 higher than the values from Leblanc et al. (2017)), and that the ionization frequency from electron impact must be higher in the anti-Jovian hemisphere for the G2 flyby conditions.

Journal article

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