Electron Densities in the Ionosphere of Mars: Comparison of MAVEN/ROSE and MAVEN/LPW Measurements

Abstract

An ionosphere is a region of thermal plasma of planetary origin (i.e., as opposed to solar wind origin) that is found within and above the upper atmosphere of a solar system body (Bauer & Lammer, 2004;Schunk & Nagy, 2009;Witasse et al., 2008). An ionosphere is part of the interface between the gravitationally controlled neutral environment of the solar system body (e.g., atmosphere and interior) and the electromagnetically controlled plasma environment that surrounds it (i.e., magnetosphere and solar wind; i.e., Cravens, 2004;Schrijver & Siscoe, 2010;Schunk & Nagy, 2009). As such, an ionosphere plays an important role in mediating coupling between these two domains, including the transfer of mass, momentum, and energy.Ionospheric plasma is generally produced by the photoionization of neutral atmospheric species. The primary ions produced by photoionization may undergo further chemical reactions with those neutral atmospheric species, such as charge exchange reactions that modify the abundances of ion species (Bauer & Lammer, 2004;Hargreaves, 1992;Schunk & Nagy, 2009). Hence, ionospheric properties reflect conditions in the neutral upper atmosphere. Ionospheric processes can also influence neutral atmospheric conditions (a) chemically, by participating in chemical reactions that produce and destroy neutral atmospheric species; (b) dynamically, by collisions between plasma and neutrals; and (c) energetically, by either transfer of thermal energy from the relatively warm plasma to the relatively cool neutral atmosphere or by Joule heating. Over longer timescales, ionospheric processes can also affect the total mass of the atmosphere. Many atmospheric escape processes that can lead to loss of atmospheric species and reduction in surface pressure involve the ionosphere. One such process is photochemical escape (e.g.,

Troubles in Mars Ionosphere Modeling

“…Nevertheless, more comprehensive reports on intercalibrations between relevant MAVEN instruments would provide guidance and clarity on this topic. For example, comparisons of total ion density/electron density measurements from the LPW, NGIMS, ROSE, and STATIC instruments could be reported, similar to a recent comparison of ROSE and LPW electron density measurements (Felici et al., 2022). Similarly, comparisons of individual ion density measurements from the NGIMS and STATIC instruments or of bulk neutral density from the NGIMS and ACC instruments could be reported.…”

“…The MAVEN NGIMS instrument (Benna et al, 2015;Mahaffy, Benna, King, et al, 2015;Mahaffy, Benna, Elrod, et al, 2015;Stone et al, 2018) measures ionospheric density and composition. Other MAVEN instruments, including LPW, the SupraThermal And Thermal Ion Composition (STATIC) instrument (Fowler et al, 2022;Hanley et al, 2021Hanley et al, , 2022McFadden et al, 2015) and the Radio Occultation Science Experiment (ROSE) (Felici et al, 2022;Withers et al, 2020Withers et al, , 2022Withers et al, , 2023, can also measure ionospheric conditions.…”

Characteristic Timescales for the Dayside Martian Ionosphere: Chemistry, Diffusion, and Magnetization

“…According to Figure 3, the situation for the duskside is close to that for the dayside, whereas the situation for the dawnside is close to that for the nightside, both featuring similar locations of the PCE boundary for the two displayed species. The above difference between the dawnside and duskside could be viewed as one aspect of the well-established dawn-dusk asymmetry of the Martian ionosphere (e.g., Cao et al 2019;Cui et al 2020;Felici et al 2022). For instance, it is consistent with the observation that the ion distribution on the duskside extends further into the darkness as compared to the dawnside, especially at low altitudes (Cao et al 2019).…”

“…First, all boundaries tend to be higher at high solar activity than at low solar activity, in response to the solar cycle variations of the Martian upper atmosphere and ionosphere, with enhanced solar EUV and SXR irradiance causing stronger ionization, higher neutral and plasma concentrations, more frequent ionneutral and ion-ion collisions, and slower diffusion. Second, all boundaries show similarly elevated locations on the dayside and duskside as compared to the nightside and dawnside, a feature that is naturally driven by the diurnal cycle of the ambient atmosphere and ionosphere and is also an important aspect of the dawn-dusk asymmetry of the Martian ionosphere (e.g., Cao et al 2019;Cui et al 2020;Felici et al 2022). Third, no boundaries show significant variations with the magnetic field environment, except for the PCE boundary, which tends to be elevated in strongly magnetized regions.…”