Increased and Varied Radiation during the Sun's Encounters with Cold Clouds in the last 10 million years

TL;DR

The paper suggests that during the Sun's encounters with cold interstellar clouds over the past 10 million years, Earth experienced prolonged periods of increased high-energy radiation exposure, impacting climate and biodiversity.

Contribution

It introduces the concept of Heliospheric Energetic Particles (HEPs) and quantifies their intensity during historical solar encounters with interstellar clouds, highlighting prolonged radiation exposure.

Findings

Earth was exposed to significantly increased high-energy particle radiation during solar-cloud encounters.

Prolonged HEP exposure lasted several months, unlike modern short-duration solar events.

Galactic cosmic ray intensity was at least ten times higher outside the heliosphere.

Abstract

Recent research raises the possibility that 3 and 7 million years ago, the Sun encountered massive clouds that shrank the heliosphere--the solar cocoon protecting our solar system--exposing Earth to its interstellar environment, in agreement with geological evidence from 60Fe and 244Pu isotopes. Here we show that during such encounters Earth was exposed to increased radiation in the form of high-energy particles. During periods of Earth's immersion in the heliosphere, it received particle radiation that we name Heliospheric Energetic Particles (HEPs). The intensity of < 10 MeV protons was at least an order of magnitude more intense than today's most extreme solar energetic particle (SEP) events. SEPs today last minutes to hours, but HEP exposure then lasted for extensive periods of several months, making it a prolonged external driver. During Earth's excursion outside the heliosphere, it was exposed to a galactic cosmic ray radiation with the intensity of < 1 GeV protons at least an order of magnitude more intense than today. Therefore, the space surrounding Earth was permeated by a variable high-energy radiation. We discuss the implications for Earth's climate and biodiversity.