Unlike Earth and Venus, Mars with a weak gravity allows an extended corona of hot light species and the escape of its lighter and hotter constituents in its exosphere. Being the most important reaction, the dissociative recombination of O₂⁺ is responsible for most of the production of hot atomic oxygen deep in the dayside thermosphere/ionosphere. The physics of the Martian upper atmosphere is complicated by the change in the flow regime from a collisional to collisionless domain with increasing altitude. Previous studies of the Martian hot corona used simple extrapolations of 1D thermospheric/ionospheric parameters and could not account for the full effects of realistic conditions, which are shown here to be of significant influence on the exosphere both close to and far away from the exobase.

In this work, a 3D physical and chemical kinetic model of the Martian upper atmosphere has been developed and employed in combination with various thermospheric/ionospheric inputs to present, for the first time, a complete 3D self-consistent description of the exosphere via a global probabilistic technique.

A 3D analysis and shape of the Martian hot corona is provided, along with density and temperature profiles of cold and hot constituents as functions of position on the planet (altitude, latitude and longitude). In addition, several of the limiting cases spanning spatial and temporal domains are examined. The variations in the Martian upper atmosphere over modern and past conditions are investigated. These characteristic conditions lead to significant variations in the thermosphere/ionosphere temperatures, dynamical heating, winds and ion/neutral density distributions, which in turn affect the general structure of the exosphere, shape of the hot corona, and the ion/neutral loss rates on all timescales.

Spatial, seasonal, solar cycle and evolutionary driven variations, although exhibiting very different timescales, are all shown to exert an influence on the atmospheric loss of the same order. Atmospheric loss and ion production, calculated locally all around the planet, provide valuable information for plasma models, refining the understanding of the ion loss, atmospheric sputtering, and interaction with the solar wind in general.