Mars’ nightside sky is lit by auroras that should not be there, and this project will find out why. Unlike Earth, Mars lacks a global magnetic field. Patches of ancient crustal magnetism create a tangled, hybrid magnetosphere where the solar wind drags magnetic field lines into a long tail behind the planet. Recent spacecraft observations have revealed auroral glows and extreme ionization layers across the nightside—sometimes linked to solar storms, sometimes appearing on their own. This suggests that particles are constantly streaming along the magnetotail into and out of the atmosphere, but no one has systematically mapped those pathways. This research will combine data from every available Mars mission—including the upcoming EscaPADE orbiters—with numerical modelling to trace how cold ionospheric plasma escapes into space and how auroral emissions are triggered. It will answer two specific questions: what tail dynamics control Martian aurora, and what drives ionospheric plasma outflow to high altitudes on the nightside. The work is fundamental science. It will not immediately change anything on Earth. But understanding how a weakly magnetised planet loses its atmosphere over geological time has direct implications for comparative planetology—including why Earth kept its atmosphere while Mars did not, and what to expect around magnetised and unmagnetised exoplanets. It will also help assess radiation and plasma hazards for future robotic and human missions to Mars.
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The interaction of the solar wind with a planet is a critical process that determines the properties of the near-planet environment. This is particularly important at Mars, where remnant crustal magnetic fields from some parts of its surface directly interact with the solar wind creating a complex hybrid magnetosphere with a myriad of draped, closed and open field lines continuously intertwining on the nightside of the planet. Recent major discoveries have shown that extreme ionization layers can be found in the nightside ionosphere, coincident with surprising very large auroral activity that sometimes is dependent on space weather activity and other times is found to be independent, and can be found everywhere over the nightside of Mars. These findings suggest clear mechanisms guiding particle motion in the magnetotail into and out of the atmosphere at all times, and not only during space weather activity. The goal of this proposal is to perform the first systematic characterization of the coupling between the highly dynamic environment in Mars' magnetotail and the nightside ionosphere. We will characterise the role of crustal and interplanetary magnetic fields in the region, the production of auroral emissions and the response of the ionosphere, allowing us to identify the mechanisms leading to the major “highway” of particle motion in the system both towards and away from the planet’s atmosphere. This project builds on strong heritage and is organised as a pair of exciting, novel and cutting-edge work packages focusing on the Martian tail pathways, in order to answer: What is the relationship between lower ionospheric layers and auroral emissions? What tail dynamics controls the Martian aurora? How does ionospheric plasma (cold plasma, ~1 eV) travel to high altitudes in the nightside tail? What factors influence ionospheric plasma outflow from the upper nightside ionosphere into space? The work packages require data from all available missions at Mars, including the upcoming EscaPADE mission, covering the whole system and focusing on tail dynamics. It will be complemented with numerical ionospheric-auroral modelling. This extremely timely world-leading research will transform our current understanding of the dynamics of the Mars space environment, with important implications for comparative planetology in our Solar System and beyond (i.e., for exoplanets), especially to comprehend the role of magnetospheres on atmospheric escape and radiation environments. It will also inform future robotic and human exploration of Mars, fully aligning with STFC’s strategy.
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