Escape of CO2+ and Other Heavy Minor Ions From the Ionosphere of Mars. Issue 1 (11th January 2021)

• Record Type: Journal Article
• Authors: Maes, Lukas; Fraenz, Markus; McFadden, James P.; Benna, Mehdi
• Is Part Of: Journal of geophysical research. Volume 126:Issue 1(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-01-11
• Subjects: Mars -- Ionosphere -- Escape -- Composition -- CO2+ -- Atmospheric erosion; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2020JA028608
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Ionospheric escape from Mars is an important process for the erosion of the Martian atmosphere. The heavy ion outflow is dominated by O 2 + ${\mathrm{O}}_{2}^{+}$ and O +, however, the Martian ionosphere consists of many more ion species. In the dayside ionosphere below roughly 220 km altitude, CO 2 + ${\mathrm{CO}}_{2}^{+}$ is the second most dominant ion, and higher up and in the nightside ionosphere other ions species with a mass near but below that of O 2 + ${\mathrm{O}}_{2}^{+}$ (28–30 Atomic Mass Unit [AMU], e.g., CO +, N 2 + ${\mathrm{N}}_{2}^{+}$, HCO +, NO +, etc.) gain in importance. However, their contribution to the ionospheric outflow is often obscured by the dominant ions O 2 + ${\mathrm{O}}_{2}^{+}$ and O + . Therefore, we perform a peak fitting to the mass spectrum of SupraThermal and Thermal Ion Composition onboard Mars Atmosphere and Volatile EvolutioN. This method is validated against the mass spectrum given by Neutral Gas and Ion Mass Spectrometer, and results in the ionosphere agree qualitatively very well. A statistical study is then performed to study the low‐energy (<100 eV) heavy ion outflow. We find that CO 2 + ${\mathrm{CO}}_{2}^{+}$ can be seen throughout the Martian magnetosphere, but it escapes only in small amounts at a mean rate of less than 1% of the O 2 + ${\mathrm{O}}_{2}^{+}$ rate. On the other hand, we find that the ions with a mass from 28 to 30 AMU, which were previously unknown in the Martian ion escape, are an important part of the ionospheric outflow, with a mean escape rate that reaches 32% of the O 2 + ${\mathrm{O}}_{2}^{+}$ rate. Key Points: Escaping ionospheric CO 2 + ${\mathrm{CO}}_{2}^{+}$ is observed throughout the induced Martian magnetosphere CO 2 + ${\mathrm{CO}}_{2}^{+}$ escapes in small amounts at a rate of 1.3 × 10 22 ions s −1, which is less than 1% of the O 2 + ${\mathrm{O}}_{2}^{+}$ escape rate Ions with a mass from 28 to 30 Atomic Mass Unit form a significant, but previously unknown, part of the outflow, reaching 32% of the O 2 + ${\mathrm{O}}_{2}^{+}$ escape rate