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Magnetospheres of Terrestrial Exoplanets and Exomoons

Presentation #403.05 in the session “Exoplanets and Systems: Terrestrial Planet Atmospheres 1”.

Published onOct 26, 2020
Magnetospheres of Terrestrial Exoplanets and Exomoons

It has been well known that terrestrial planets are created from the impact of two or more protoplanets. The prevailing model for the generation of our Moon is the giant impact hypothesis in which a Mars sized object impacted the proto-Earth during the early formation of the solar system. The resulting debris formed Earth and the Moon, ending with the Moon lying just outside the Roche limit of ~2.9 Re. Over the last several years as paleomagnetists began a careful reexamination of all of the returned Apollo lunar samples, paleomagnetic measurements now make clear that a significant lunar magnetosphere must have existed for the first several 100 million years. It is expected that in stellar systems with Jovian-type planets their moons would probably be embedded within the giant planet’s magnetosphere, but what about terrestrial planets which forms moons in the terrestrial domain. We can begin the investigation of this configuration by using the Earth-Moon example where they each generate magnetospheres soon after forming. How would these two magnetospheres interact, and what protection would such a combined magnetosphere afford to the atmospheres of early exoplanets and their moons? In this paper we modeled two dipole fields simulating the main field of the exoplanet and the exomoon when the Moon was at several locations ranging from 4 to 18 Rp from the exoplanet, and under two diurnal configurations in a stellar wind environment. Clear features emerge as a consequence of the reconnected field lines between exoplanet and its moon. For the exomoon on the dayside, the polar cusp moves poleward by ~10 degrees, largely cutting off direct stellar wind access. In addition, the exomoon magnetosphere would take the brunt of the stellar wind and provide a significant additional effective shield to exoplanet’s atmosphere. With the exomoon on the nightside, the extensive reconnection of magnetic fields disrupts the expected exoplanet plasma sheet and captures much of the evaporated exoplanet’s ionospheric plasma onto the exomoon. The results of our magnetic field topological modeling demonstrate exoplanet-exomoon coupled magnetospheres work together to protect the early atmospheres of both the exoplanet and the exomoon. At times when the exomoon is on the dayside the moon’s magnetosphere would provide a significant additional buffer from the expected intense stellar wind, reducing exoplanet’s atmospheric loss to space. In addition, magnetic reconnection would create a critical pathway for the atmosphere exchange between the early exoplanet and exomoon.

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