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When the solar wind reaches the Mars obstacle, mass loading by planetary ions slows down the solar wind and raises the bow shock. The Martian atmosphere is undergoing the a scavenging by the solar wind without the protection of a global magnetic field. Atmospheric escape is an important process for the evolution of the Martian climate. For present Mars, the dominant escape of atmospheric neutrals is through four channels: Jeans escape, photochemical reactions, sputtering and electron impact ionization. Ions above the exobase get accelerated by the solar wind electric field and can escape.

We here apply a new method for estimating heavy ion (O⁺, O⁺₂, and CO⁺₂) escape rates at Mars, which combines a hybrid model and observations. We use observed upstream solar wind parameters as input for a hybrid plasma model, where the total ion upflux at the exobase is a free parameter. We then vary this ion upflux to find the best fit to the observed bow shock location. This method gives us a self-consistent description of the Mars-solar wind interaction, which can be used to study other properties of the solar wind interaction besides escape.

När solvinden stöter på Mars så tyngs den ner av joner från planeten, vilket bromsar solvinden och expanderar bogshocken. Mars atmosfär eroderas av solvinden eftersom planeten saknar ett globalt magnetfält. Atmosfärsförlust är en viktig process i hur Mars klimat förändras. För nuvarande Mars är det fyra dominerande processer för förlust av neutrala atomer: Jeans förlust, fotokemiska reaktioner, sputtering och elektronkollisionsjonisering. Joner ovan exobasen accelereras av solvinden och kan förloras. Här använder vi en ny metod för att uppskatta förlusten av tunga joner (O⁺, O⁺₂ , and CO⁺₂) vid Mars, som kombinerar en hybridmodell och observationer. Vi använder observerade solvindsparametrar som indata till en hybrid plasmamodell, där totalt jonuppflöde vid exobasen är en fri parameter. Vi varierar sedan detta jonuppflöde för att hitta bästa passningen till den observerade positionen för bogshocken. Metoden ger en självkonsistent beskrivning av Mars växelverkan med solvinden, som kan användas till att studera andra egenskaper av växelverkan, förutom jonförlust.

As the solar wind reaches Mars, planetary ions mass-load the flow, slowing it down and creating a bow shock upstream of the planet. The convective electric field, coming from the solar wind flow and solar wind magnetic field, results in a potential difference across the conducting ionosphere that in turn results in induction currents flowing through the conductor (unipolar induction). The magnetic fields associated with the induction currents cancel (or reduce due to finite conductivity) the magnetic field inside the ionosphere (Lenz’s law). Above the ionosphere, the induced fields act on the solar wind plasma by deviating it, thus a void called an induced magnetosphere is created. Without a global magnetic field, Mars’ atmosphere is eroded by the solar wind, an ongoing atmospheric escape that has significantly influenced its climatic evolution. For present Mars, the dominant escape of atmospheric neutrals is through four channels: Jeans escape, photochemical reactions, sputtering and electron impact ionization, while ions above the exobase are accelerated by the solar wind convective electric field to escape.

In this study, we introduce a new method for estimating heavy ion (O+, O+2, and CO+2) escape rates from Mars, combining a hybrid plasma model with observational data. We use observed upstream solar wind parameters as input for a hybrid plasma model, where the total ion upflux at the exobase is a free parameter. We then vary this ion upflux to find the best fit to the observed bow shock location. This method gives us a self-consistent description of the Mars-solar wind interaction, which enables broader analyses of the interaction’s properties, beyond just escape.

We investigate the influence of external factors, solar EUV radiation, solar wind dynamic pressure, interplanetary magnetic field (IMF) strength, and IMF cone angle on Martian heavy ion escape. Our results reveal that ion escape increases with stronger EUV radiation and solar wind dynamic pressure, but decreases with a higher IMF strength and cone angle. In an extreme case study when the solar wind flowis nearly aligned with the solar IMF, the induced magnetosphere of Mars degenerates, and the bow shock on the dayside disappears, ions flowing towards the sun are accelerated by the ambipolar field, and a large-scale E×B cross-flow structure forms, dramatically increasing ionescape. We therefore call this type of interaction a degenerate induced magnetosphere. Finally, we compare the interactions of Mars and Venus in response to similar solar wind conditions, finding significant similarities in their responses as unmagnetized planets, further informing our understanding of atmospheric escape and solar wind interactions with unmagnetized bodies.