Evidence of the Rayleigh Taylor Instability at Mars

Equatorial spread F (ESF) is commonly observed in the terrestrial equatorial ionosphere and results in highly disturbed ionospheric conditions. For example, variations in ionospheric density on the order of 100% are typically observed and these can impact the propagation of radio waves through the terrestrial ionosphere. The Rayleigh Taylor instability is one of the primary onset mechanisms for ESF. We present candidate observations of the Rayleigh Taylor instability made by the MAVEN spacecraft in the Martian ionosphere, to our knowledge the first of their kind at Mars. A statistical study of similar events shows that they occur primarily at the Martian terminator, where the magnetic field topology and geometry with respect to the Sun appear to play a pivotal role in forming the conditions necessary for this instability to arise. The instability drives vertical ion motion and neutral winds, and may be a source of sustaining the Martian nightside ionosphere.