A cometary origin for martian atmospheric methane

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

“…Thus, a meteor shower flux onto Mars of the order of 10 8 kg required to generate the Mumma et al (2009) methane plume would have to be an extraordinary event. Even if the Mumma et al (2009) is in error by an order of magnitude as proposed by Zahnle (2011), other measurements in the 10s of ppbv of methane exist (see Table 1 of Fries et al, 2016). Therefore, a meteor shower delivering three or four orders of mass more than the typical flux is needed to generate methane in the tens of ppbv as Crismani et al (2017) state.…”

“…First, I would like to extend thanks to Crismani et al for their commentary, which highlights an important uncertainty acknowledged in Fries et al (2016), namely whether the total mass of infall material required to produce the observed methane is on par with that available from meteor showers. I would like to disagree on two points presented in the letter, and then discuss the implications of their findings.…”

“…Siding Spring was not discussed in detail in Fries et al (2016) for two reasons. For one, this encounter was a strongly atypical event, and it is not certain that it compares well with a typical meteor shower.…”

“…As such, it is not surprising that MSL has not reported an increase in methane even if the Siding Spring encounter produced the gas. This is the second, and more important, reason why Siding Spring did not feature in Fries et al (2016)-without a robust measurement for methane to test whether the gas is produced, the encounter is interesting as a study of an anomalous encounter, but of very limited utility in testing the hypothesis of a meteor shower origin for martian methane plumes (hereafter "the hypothesis").…”

“…On Earth, storms of this magnitude are estimated to occur about once per century (Beech et al, 1995), which would seem to degrade this rationale as a source of martian methane plumes, given that the literature includes four methane plumes of ~10 ppbv and two in the tens of ppbv range since 1988 (see Table 1, Fries et al, 2016). However, many more comets interact with Mars than with Earth.…”