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The Impact of Energetic Particles on the Martian Ionosphere During a Full Solar Cycle of Radar Observations: Radar Blackouts

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posted on 17.06.2022, 14:24 authored by Mark Lester, Beatriz Sanchez‐Cano, Daniel Potts, Rob Lillis, Marco Cartacci, Fabrizio Bernardini, Roberto Orosei, Matthew Perry, Nathaniel Putzig, Bruce Campbell, Pierre‐Louis Blelly, Steve Milan, Hermann Opgenoorth, Olivier Witasse, Elena MM Redrojo, Aaron Russell
We present the first long-term characterization of ionization layers in the lower ionosphere of Mars (below ∼90 km), a region inaccessible to orbital in-situ observations, based on an analysis of radar echo blackouts observed on Mars Express and the Mars Reconnaissance Orbiter from 2006 to 2017. A blackout occurs when the expected surface reflection is partly or totally attenuated for portions of an observation. Enhanced ionization at altitudes of 60–90 km, below the main ionospheric electron density peak, leads to increased absorption of the radar signal, resulting in the blackouts. We find that (a) MARSIS, operating at frequencies between 1.8 and 5 MHz, suffered more blackouts than SHARAD, which has a higher carrier frequency (20 MHz), (b) there is a clear correlation of blackout occurrence with solar cycle, (c) there is no apparent relationship between blackout occurrence and crustal magnetic fields, and (d) blackouts occur during both nightside and dayside observations, although the peak occurrence is deep on the nightside. Analysis of Mars Atmosphere and Volatile EvolutioN Solar Energetic Particle electron counts between 20 and 200 keV demonstrates that these electrons are likely responsible for attenuating the radar signals. We investigate the minimum SEP electron fluxes required to ionize the lower atmosphere and produce measurable attenuation. When both radars experience a blackout, the SEP electron fluxes are at their highest. Based on several case studies, we find that the average SEP spectrum responsible for a blackout is particularly enhanced at its higher energy end, that is, above 70 keV.


Mark Lester, Beatriz Sanchez-Cano and Steve Milan. acknowledge support through UK-STFC Grant ST/S000429/1. Beatriz Sanchez-Cano. also acknowledges support through STFC Ernest Rutherford Fellowship ST/V004115/1. D.P. acknowledges support through the Summer Undergraduate Research Experience (SURE) program of the University of Leicester. Marco Cartacci, Roberto Orosei and Fabrizio Bernardini. gratefully acknowledge support from the Italian Space Agency (ASI) through contract 2019-21-HH.0. Hermann Opgenoorth acknowledges support from the Swedish National Space Agency, SNSA. Matthew Perry and Nathaniel Putzig gratefully acknowledge support from NASA's Mars Reconnaissance Orbiter mission. The AMDA science analysis system provided by the Centre de Données de la Physique des Plasmas (CDPP) supported by CNRS, CNES, Observatoire de Paris, and Université Paul Sabatier, Toulouse is gratefully acknowledged. We also thank Renato Croci, at ThalesAleniaSpace (Rome), for helpful discussions.



Lester, M., Sanchez-Cano, B., Potts, D., Lillis, R., Cartacci, M., Bernardini, F., et al. (2022). The impact of energetic particles on the Martian ionosphere during a full solar cycle of radar observations: Radar blackouts. Journal of Geophysical Research: Space Physics, 127, e2021JA029535.

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Journal of Geophysical Research: Space Physics








American Geophysical Union (AGU)





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