Past and future preservation of the terrestrial hydrosphere by Earth’s magnetic field

Abstract:

The degree to which a magnetosphere protects a planetary atmosphere can be described as a competition between trapping of charged solar wind particles and the prevention of energy and momentum exchange with that atmosphere. Earth provides the best opportunity to categorize the long term interaction as a model for understanding the evolution of other planets and exoplanets. We have found that while a greater total solar wind mass has been captured for most of Earth’s history relative to a hypothetical planet without a magnetosphere, less solar wind energy was transferred resulting in a net protection (Blackman and Tarduno, MNRAS, 2018). Moreover, the geodynamo’s presence was especially important at two critical stages of Earth’s evolution leading to preservation of the hydrosphere. The Hadean to Paleoarchean geodynamo (Tarduno et al., PNAS, 2020) was likely central to preventing energy transfer and atmosphere blow-off. Nevertheless, extreme solar wind pressure probably removed some water from the early Earth (Tarduno et al., Science, 2010). The regeneration of the geodynamo following its near collapse in the Ediacaran (ca. 565 million years ago) by the onset of inner core nucleation (Bono et al., Nat. Geoscience, 2019) was crucial for the long term preservation of the hydrosphere because the development of an oxygenated atmosphere more vulnerable to solar wind erosion. However, when we further consider polar focusing and the future Earth, the magnetosphere could result in a greater polar energy flux as compared to an unmagnetized planet. In this case, the degree of loss will depend on the efficiency of ion trapping by the magnetosphere and return to the atmosphere.