Plasma observations during the Mars atmospheric "plume" event of March-April 2012

TL;DR

This paper analyzes plasma data from Mars during the 2012 atmospheric plume event, suggesting a possible link to a large interplanetary coronal mass ejection affecting the Martian ionosphere.

Contribution

It provides the first in-situ plasma measurements during the plume event and proposes a novel connection between ICMEs and high-altitude plumes on Mars.

Findings

Plasma measurements show disturbed ionospheric structures during the event.

The plume's brightness and altitude exceed typical auroral and cloud formation expectations.

A potential link between ICMEs and plume formation is suggested.

Abstract

We present initial analysis and conclusions from plasma observations made during the reported "Mars plume event" of March - April 2012. During this period, multiple independent amateur observers detected a localized, high-altitude "plume" over the Martian dawn terminator [Sanchez-Lavega et al., Nature, 2015, doi:10.1038/nature14162], the cause of which remains to be explained. The estimated brightness of the plume exceeds that expected for auroral emissions, and its projected altitude greatly exceeds that at which clouds are expected to form. We report on in-situ measurements of ionospheric plasma density and solar wind parameters throughout this interval made by Mars Express, obtained over the same surface region, but at the opposing terminator. Measurements in the ionosphere at the corresponding location frequently show a disturbed structure, though this is not atypical for such regions with intense crustal magnetic fields. We tentatively conclude that the formation and/or transport of this plume to the altitudes where it was observed could be due in part to the result of a large interplanetary coronal mass ejection (ICME) encountering the Martian system. Interestingly, we note that the only similar plume detection in May 1997 may also have been associated with a large ICME impact at Mars.