The Impact of Comet Siding Spring's Meteors on the Martian Atmosphere and Ionosphere

Abstract

On 19 October 2014, comet C/2013 A1 (Siding Spring) had a close encounter with Mars and deposited cometary dust particles into the Martian atmosphere. We report a comprehensive analysis of the resulting meteor shower and its perturbation on Mars' atmosphere and ionosphere. Using Mars Atmosphere and Volatile EvolutioN/Imaging Ultraviolet Spectrograph observations of ablated meteoric metallic species, we show this shower lasted less than 3 hr and was therefore limited to one hemisphere. Meteoric ablation occurred in a narrow altitude layer, with Mg+, Mg, Fe+, and Fe deposited between about 105 and 120 km, consistent with comet Siding Spring's relative velocity of 56 km/s. We find that 82 ± 25 t of dust was deposited, improving previous measurements and a thousand times larger than model expectations. With regular observations over two Mars days, we show that horizontal winds globally redistribute this material and also suggest new vertical transport mechanisms for metallic ions. Such transport is inconsistent with diffusion and may be related to electrodynamic processes. The rapid loss of neutral species and presence of ions at high altitudes indicate that our understanding of existing Martian meteoric chemistry modeling and ionospheric dynamics is incomplete.

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

“…This paper has shown in situ electron density observations of the Northern Hemisphere at CA, while previous studies have shown other aspects of the encounter, such as in situ effects of cometary dust in the Southern hemisphere and subsequent redistribution of the dust by atmospheric circulation during the following days after the encounter (e.g., Crismani et al, 2018;Gurnett et al, 2015), the large variability of cometary magnetic field (e.g., Espley et al, 2015), and the shower of energetic particles that the comet produced over Mars (e.g., Sánchez-Cano et al, 2018). This paper has shown in situ electron density observations of the Northern Hemisphere at CA, while previous studies have shown other aspects of the encounter, such as in situ effects of cometary dust in the Southern hemisphere and subsequent redistribution of the dust by atmospheric circulation during the following days after the encounter (e.g., Crismani et al, 2018;Gurnett et al, 2015), the large variability of cometary magnetic field (e.g., Espley et al, 2015), and the shower of energetic particles that the comet produced over Mars (e.g., Sánchez-Cano et al, 2018).…”

“…However, Crismani et al (2018) found in a comprehensive analysis that the meteor shower lasted less than 3 hr, was limited to one hemisphere and that horizontal winds globally redistributed this material over the next 2 days. However, Crismani et al (2018) found in a comprehensive analysis that the meteor shower lasted less than 3 hr, was limited to one hemisphere and that horizontal winds globally redistributed this material over the next 2 days.…”

“…In particular, a total dust mass of 82 ± 25 t was deposited in Mars' atmosphere, creating an ionospheric layer of metallic ions between 105 and 120 km altitude (Benna et al, 2015;Crismani et al, 2018;Schneider et al, 2015) as measured by the Mars Atmosphere and Volatile Evolution (MAVEN) mission. In particular, a total dust mass of 82 ± 25 t was deposited in Mars' atmosphere, creating an ionospheric layer of metallic ions between 105 and 120 km altitude (Benna et al, 2015;Crismani et al, 2018;Schneider et al, 2015) as measured by the Mars Atmosphere and Volatile Evolution (MAVEN) mission.…”

“…In addition, dust ejected from the comet remained confined in a debris stream that lagged behind the comet in its orbit and intercepted the Martian Southern hemisphere. The peak dust flux occurred between 19:59 and 20:09 on 19 October, when Mars crossed the comet's orbital plane, and the dust shower lasted less than 3 hr (Crismani et al, 2018). During CA, Mars was partly blocking the dust stream and forming a shadow area for dust impacts in the Northern hemisphere (Positions p1 and p2 in Figure 2a, reddish cylinder in Figure 2b), where MEX had been placed to keep the spacecraft away from direct dust impact.…”

“…Focusing on the dust, electrons within the ionosphere can be lost due to dust attachment. However, MAVEN observed that~82 t dust were deposited in Mars' atmosphere over~3 hr and limited to the Martian hemisphere facing the comet (the opposite hemisphere to where MEX was) (Crismani et al, 2018). Preliminary results from the Planetary Fourier Spectrometer (PFS) (Formisano et al, 2005) on board MEX indicated an increase of the atmospheric dust opacity, after the comet's CA, especially in the latitude range 40°S-10°N (Giuranna et al, 2017).…”