Time-variability in the Interstellar Boundary Conditions of the Heliosphere: Effect of the Solar Journey on the Galactic Cosmic Ray Flux at Earth

TL;DR

This paper investigates how the solar journey through different interstellar environments affects the heliosphere and consequently modulates galactic cosmic ray fluxes at Earth, impacting cosmogenic isotope records and Earth's climate history.

Contribution

It models the effects of variable interstellar conditions on the heliosphere and cosmic ray flux, linking interstellar transitions to geologic radionuclide records.

Findings

Interstellar environment changes can significantly alter cosmic ray flux at Earth.

Cosmogenic radionuclide records are consistent with interstellar cloud transitions during the Holocene.

Adjustment of geomagnetic timelines may be needed due to changes in anomalous cosmic rays.

Abstract

During the solar journey through galactic space, variations in the physical properties of the surrounding interstellar medium (ISM) modify the heliosphere and modulate the flux of galactic cosmic rays (GCR) at the surface of the Earth, with consequences for the terrestrial record of cosmogenic radionuclides. One phenomenon that needs studying is the effect on cosmogenic isotope production of changing anomalous cosmic ray fluxes at Earth due to variable interstellar ionizations. The possible range of interstellar ram pressures and ionization levels in the low density solar environment generate dramatically different possible heliosphere configurations, with a wide range of particle fluxes of interstellar neutrals, their secondary products, and GCRs arriving at Earth. Simple models of the distribution and densities of ISM in the downwind direction give cloud transition timescales that can be directly compared with cosmogenic radionuclide geologic records. Both the interstellar data and cosmogenic radionuclide data are consistent with cloud transitions during the Holocene, with large and assumption-dependent uncertainties. The geomagnetic timeline derived from cosmic ray fluxes at Earth may require adjustment to account for the disappearance of anomalous cosmic rays when the Sun is immersed in ionized gas.