Imperial College London


Faculty of Natural SciencesDepartment of Physics

Reader in Planetary Science



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Publication Type

128 results found

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, Pages: 104924-104924, ISSN: 0032-0633

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

Hajra R, Henri P, Vallières X, Galand M, Rubin M, Tsurutani BT, Gilet N, Bucciantini L, Nemeth Zet al., 2020, Ionospheric total electron content of comet 67P/Churyumov-Gerasimenko, Astronomy & Astrophysics, Vol: 635, Pages: A51-A51, ISSN: 0004-6361

We study the evolution of a cometary ionosphere, using approximately two years of plasma measurements by the Mutual Impedance Probe on board the Rosetta spacecraft monitoring comet 67P/Churyumov-Gerasimenko (67P) during August 2014–September 2016. The in situ plasma density measurements are utilized to estimate the altitude-integrated electron number density or cometary ionospheric total electron content (TEC) of 67P based on the assumption of radially expanding plasma. The TEC is shown to increase with decreasing heliocentric distance (rh) of the comet, reaching a peak value of ~(133 ± 84) × 109 cm−2 averaged around perihelion (rh < 1.5 au). At large heliocentric distances (rh > 2.5 au), the TEC decreases by ~2 orders of magnitude. For the same heliocentric distance, TEC values are found to be significantly larger during the post-perihelion periods compared to the pre-perihelion TEC values. This “ionospheric hysteresis effect” is more prominent in the southern hemisphere of the comet and at large heliocentric distances. A significant hemispheric asymmetry is observed during perihelion with approximately two times larger TEC values in the northern hemisphere compared to the southern hemisphere. The asymmetry is reversed and stronger during post-perihelion (rh > 1.5 au) periods with approximately three times larger TEC values in the southern hemisphere compared to the northern hemisphere. Hemispheric asymmetry was less prominent during the pre-perihelion intervals. The correlation of the cometary TEC with the incident solar ionizing fluxes is maximum around and slightly after perihelion (1.5 au < rh < 2 au), while it significantly decreases at larger heliocentric distances (rh > 2.5 au) where the photo-ionization contribution to the TEC variability decreases. The results are discussed based on cometary ionospheric production and loss processes.

Journal article

Cao Y, Wellbrock A, Coates AJ, CaroCarretero R, Jones GH, Cui J, Galand M, Dougherty MKet al., 2020, Field‐aligned photoelectron energy peaks at high altitude and on the nightside of titan, Journal of Geophysical Research: Planets, Vol: 125, Pages: 1-13, ISSN: 2169-9097

The ionization of N urn:x-wiley:jgre:media:jgre21272:jgre21272-math-0001 by strong solar He II 30.4‐nm photons produces distinctive spectral peaks near 24.1 eV in Titan's upper atmosphere, which have been observed by the Electron Spectrometer (ELS) as part of the Cassini Plasma Spectrometer. The ELS observations reveal that, in addition to the dayside, photoelectron peaks were also detected on the deep nightside where photoionization is switched off, as well as at sufficiently high altitudes where the ambient neutral density is low. These photoelectron peaks are unlikely to be produced locally but instead must be contributed by transport along the magnetic field lines from their dayside source regions. In this study, we present a statistical survey of all photoelectron peaks identified with an automatic finite impulse response algorithm based on the available ELS data accumulated during 56 Titan flybys. The spatial distribution of photoelectron peaks indicates that most photoelectrons detected at an altitude above 4,000 km and a solar zenith angle above 100° are field aligned, which is consistent with the scenario of photoelectron transport along the magnetic field lines. Our analysis also reveals the presence of a photoelectron gap in the deep nightside ionosphere where almost no photoelectrons were detected. It appears to be very difficult for photoelectrons to travel to this region, and such a feature may not be driven by the changes in the orientation between the solar and corotation wakes.

Journal article

Schrijver K, Bagenal F, Bastian T, Beer J, Bisi M, Bogdan T, Bougher S, Boteler D, Brain D, Brasseur G, Brownlee D, Charbonneau P, Cohen O, Christensen U, Crowley T, Fischer D, Forbes T, Fuller-Rowell T, Galand M, Giacalone J, Gloeckler G, Gosling J, Green J, Guetersloh S, Hansteen V, Hartmann L, Horanyi M, Hudson H, Jakowski N, Jokipii R, Kivelson M, Krauss-Varban D, Krupp N, Lean J, Linsky J, Longcope D, Marsh D, Miesch M, Moldwin M, Moore L, Odenwald S, Opher M, Osten R, Rempel M, Schmidt H, Siscoe G, Siskind D, Smith C, Solomon S, Stallard T, Stanley S, Sojka J, Tobiska K, Toffoletto F, Tribble A, Vasyliunas V, Walterscheid R, Wang J, Wood B, Woods T, Zapp Net al., 2019, Principles Of Heliophysics: a textbook on the universal processes behind planetary habitability, Publisher: arXiv

This textbook gives a perspective of heliophysics in a way that emphasizesuniversal processes from a perspective that draws attention to what providesEarth (and similar (exo-)planets) with a relatively stable setting in whichlife as we know it can thrive. The book is intended for students in physicalsciences in later years of their university training and for beginning graduatestudents in fields of solar, stellar, (exo-)planetary, and planetary-systemsciences.

Working paper

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