MAVEN observations of the solar wind interaction with the Martian dayside upper ionosphere

The lack of a global dipole magnetic field at Venus and Mars means that the solar wind-planet interaction occurs much closer to these planets than at magnetized bodies, such as Earth. At Venus, the solar wind has been observed to interact with the upper ionosphere, providing a heat source for the ionospheric plasma. A similar interaction is expected to occur at Mars. Studies of energy balance in the Martian upper ionosphere have shown that observed electron temperatures are significantly greater than modeled values. Such high temperatures can have significant impacts on ionospheric escape to space, for example, via the resultant ambi-polar electric fields. Energy input to the upper ionosphere from the planet-solar wind interaction has been postulated as a likely heating source to explain these discrepancies. In this study, we present MAVEN in-situ observations of the solar wind interacting with the dayside upper ionosphere at Mars. The interaction appears to drive strong variations in suprathermal pitch angle distributions, ionospheric density, and temperature. Such observations can help constrain the energy input into the upper ionosphere, providing constraints for future modeling of the Martian ionosphere and escape to space.