A photochemical model of the dust‐loaded ionosphere of Mars

Abstract

The ionization of the lower Martian atmosphere and the presence of charged species are fundamental in the understanding of atmospheric electricity phenomena, such as electric discharges, large‐scale electric currents, and Schumann resonances. The present photochemical model of the lower ionosphere of Mars (0–70 km) is developed to compute the concentration of the most abundant charged species (cluster ions, electrons, and charged aerosols) and electric conductivity, at the landing site and epoch of the ExoMars 2016 mission. The main sources of ionization are galactic cosmic rays (during daytime as well as nighttime) and photoionization of aerosols due to solar UV radiation during daytime. Ion and electron attachment to aerosols is another major source of aerosol charging. The steady state concentration of charged species is computed by solving their respective balance equations (also known as continuity equations), which include the source and sink terms of their photochemical reactions. Since the amount of suspended dust can vary considerably and it has an important effect on atmospheric properties, several dust scenarios, in addition to the day‐night variations, are considered to characterize the variability of the concentration of charged species. It has been found that during daytime, aerosols tend to become positively charged due to electron photoemission and, during nighttime, tend to charge negatively due to electron attachment. The most dominant day‐night variability in ion and electron concentration occurs when the amount of suspended dust is the largest. The electric conductivity has been found to vary in the 10−13–10−7 S/m range, depending on the altitude, dust scenario, and local time.

Schumann resonances at Mars: Effects of the day‐night asymmetry and the dust‐loaded ionosphere

“…The results from Cardnell et al [] indicate that the Martian atmospheric conductivity varies roughly 2 orders of magnitude at ground level depending on solar illumination. Results from Figure tell us that dayside conditions cannot accommodate SR, while nightside conditions can.…”

“…The electrical properties of the Martian atmosphere‐ionosphere system are obtained from a photochemical model [ Cardnell et al , ] which uses the Mars Climate Database (MCD) [ Forget et al , ; Millour et al , ] as an input for the properties of the neutral atmosphere. The conductivity profiles used in this work are detailed in Figure S1 in the supporting information and correspond to the conditions expected during the ExoMars landing (October 2016).…”

“…The major findings that affect SR are the changing conductivity depending on the dust conditions of the atmosphere and the large day‐night asymmetry present on Mars. Therefore, we have considered the three dust scenarios defined in Cardnell et al []: low, standard, and high. The standard dust scenario corresponds to a dust distribution reconstructed from seven Martian years (years 24 to 31) of observations, where global dust storms data have been removed.…”

“…Since there are no in situ measurements of plasma properties at altitudes below 80 km on Mars, photochemical models are the best available tool to infer the electromagnetic properties [ Whitten et al , ; Molina‐Cuberos et al , , ]. Dust has been found to play a major role in the atmospheric conductivity of Mars by reducing it and enhancing the day‐night asymmetry of the Martian cavity, where the conductivity can differ by 2 orders of magnitude [ Michael et al , , ; Aplin , ; Cardnell et al , ]. In addition, a layer created by meteoric ablation at 80–90 km of altitude is known to be present [ Molina‐Cuberos et al , ; Withers et al , ].…”

Mars' Ionospheric Interaction With Comet C/2013 A1 Siding Spring's Coma at Their Closest Approach as Seen by Mars Express

“…This is well-known at low and midaltitudes in the Martian atmosphere, especially on the nightside where aerosols tend to negatively charge due to electron attachment when the level of suspended Martian dust is high (Cardnell et al, 2016). Focusing on the dust, electrons within the ionosphere can be lost due to dust attachment.…”