The Siding Spring cometary encounter with Mars: A natural experiment for the Martian atmosphere?

Abstract

On 19 October 2014 comet C/2013 A1 will encounter Mars. The planet is anticipated to pass through the coma resulting in a greater than four order-of-magnitude increase in the accretion of dust with 430 tonnes of dust with diameters between 1 μm and 12.4 mm surviving atmospheric passage. At high altitude, the dust would impact temperature and may affect limb dust extinction and cloud formation. The UV photolysis of the organic carbon content of the dust, 1.9 to 4.6 tonnes, would have a negligible effect on atmospheric methane. Should C/2013 A1 brighten, increases in upper atmospheric accretion of coma particles will exceed the background dust and the population of small coma particles may be constrained from orbital measurements. For M 1 < -1.3, methane produced might be measurable by the Sample Analysis at Mars Tunable Laser Spectrometer instrument onboard Curiosity.

Predictions of the effects of Mars's encounter with comet C/2013 A1 (Siding Spring) upon metal species in its ionosphere

“…The mass accretion rate under normal circumstances is on the order of 0.01 kg s −1 , 4 orders of magnitude smaller [Moores et al, 2014]. The validity of these numerical results is addressed in section 5.…”

“…During this encounter, the flux of interplanetary dust particles onto Mars may increase somewhat. Estimates of this increase range from practically zero [Ye and Hui, 2014;Tricarico et al, 2014] to more than 4 orders of magnitude [Moorhead et al, 2014;Moores et al, 2014].…”

“…Predictions of other effects of this encounter on the atmosphere of Mars have been made by Moores et al [2014] and Yelle et al [2014].…”

“…We combine a model of the dust population in the coma (section 2), a model of the ablation of dust particles in the atmosphere of Mars (section 3), and a model of the chemistry of metal species in the ionosphere of Mars (section 4) to predict the injection rate of metal species into the atmosphere and the associated density of metal ions in the ionosphere. Predictions of other effects of this encounter on the atmosphere of Mars have been made by Moores et al [2014] and Yelle et al [2014].…”

Reply to Comment on “A cometary origin for atmospheric martian methane” by Crismani et al., 2017

“…), while the only asset capable of searching for methane at the time was the Mars Science Laboratory (MSL) rover, which is located on the planet's surface a full ~100 km below the maximum mass deposition altitude (ibid. ), and-unfortunately-almost perfectly antipodal to the site of maximum mass input (Moores et al, 2014). As such, it is not surprising that MSL has not reported an increase in methane even if the Siding Spring encounter produced the gas.…”