Abstract
Recent research raises the possibility that 2–3 and 6–7 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.
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References
Cummings, A. C. et al. Galactic cosmic rays in the local interstellar medium: voyager 1 observations and model results. Astrophys. J. 831, 18 (21pp) (2016).
Begelman, M. & Rees, M. Can cosmic clouds cause Climatic catastrophes? Nature 261, 298–299 (1976).
Yeghikyan, A. & Fahr, H. Chapter 11 of Solar journey, the Significance of our Galactic Environment for the Heliosphere and earth, Pricilla C (Frisch Editor, 2006).
Miller, J. A. & Fields, B. D. Heliospheric compressions due to recent nearby supernova explosions. Astrophys. J. 934, 32 (13pp) (2022).
Fields, B. D., Athanassiadou, T. & Johnson, S. R. Supernova collisions with the heliosphere. Astrophys. J. 678, 549–562 (2008).
Fields, B. D. et al. Supernova triggers for end-Devonian extinctions. PNAS 117, 21008–21010 (2020).
Frisch, P. C. & Muller H-R time variability in the interstellar boundary conditions of the heliosphere: effect of the solar journey on the galactic cosmic ray flux at Earth. Space Sci. Rev. 76, 21–34 (2013).
Florinski, V. & Zank, G. P. The Galactic Cosmic Ray Intensity in the Heliosphere in Response To Variable Interstellar Environments, chap. 10 of Solar journey, the Significance of our Galactic Environment for the Heliosphere and earth, Pricilla C (Frisch Editor, 2006).
Shaviv, N. J. Cosmic ray diffusion from the galactic spiral arms, iron meteorites, and a possible Climatic connection? Phys. Rev. Lett. 89, 051102–051105 (2002).
Opher, M., Loeb, A. & Peek, J. E. G. A possible direct exposure of the Earth to the cold interstellar medium 2–3 Myr ago. Nat. Astron. 8, 983–990 (2024).
Opher, M. et al. Effect of the passage of the sun through the edge of the local bubble. Astrophys. J. 972, 201–212 (2024).
Zucker, C. et al. On the Three-dimensional structure of local molecular clouds. Astrophys. J. 919, 35 (34pp) (2021).
Opher, M. et al. Solar wind with hydrogen ion charge exchange and large-scale dynamics (SHIELD) DRIVE science center. Front. Space Sci. Astrophys. 10, 1179344: 01–26 (2023).
Wallner, A. et al. Recent near-Earth supernovae probed by global deposition of interstellar radioactive 60Fe. Nature 532, 69–72 (2016).
Wallner, A. et al. 60Fe and 244Pu deposited on Earth constrain the r-process yields of recent nearby supernovae. Science 372, 742–745 (2021).
Koll, D. et al. Interstellar 60Fe in Antarctica. Phys. Rev. Lett. 123, 072701 (2019).
Binns, W. R. et al. Observation of the 60Fe nucleosynthesis-clock isotope in galactic cosmic rays. Science 352, 677–680 (2016).
Fimiani, L. et al. Interstellar 60Fe on the surface of the Moon. Phys. Rev. Lett. 116, 151104 (2016).
McKay, C. & Thomas, G. E. Consequences of a past encounter of the Earth with an interstellar cloud geophys. Res. Lett. 5, 215–218 (1978).
Zachos, J. et al. Trends, Rhythms, and aberrations in global climate 65 Ma to present. Science 292, 686–693 (2001).
Westerhold, T. N. et al. An astronomically dated record of earth’s climate and its predictability over the last 66 million years. Science 369, 1383–1387 (2020).
Miller, J. A. et al. Earth’s mesosphere during possible encounters with massive interstellar clouds 2 and 7 Million Years Ago, Geophys. Res. Letter 51, (2024). e2024GL110174.
Ertel, A. F. & Fields, B. D. Distances to recent near-earth supernovae from geological and lunar 60Fe. Astrophys. J. 972, 179 (2024).
Gehrels, N. et al. Ozone depletion from nearby supernovae. Astrophys. J. 585, 1169 (2003).
Fry, B. J., Fields, B. D. & Ellis, J. R. Magnetic imprisonment of dusty pinballs by a supernova remnant. Astrophys. J. 894, 109 (2020).
Athanassiadou, T. & Fields, B. D. Penetration of nearby supernova dust in the inner solar system. NewA 16, 229 (2011).
Zucker, C. et al. Star. Formation Near Sun Is Driven Expansion Local. Bubble Nat. 601, 334 (2022).
Talbot, R. J., Butler, D. M. & Newman, M. J. Climatic effects during passage of the solar system through interstellar clouds nature 262, 561–563 (1976).
Talbot, R. J. & Newman, M. J. Encounters between stars and dense interstellar clouds. Ap J. Suppl. 34, 295–308 (1977).
Yabushita, S. & Allen, A. J. On the effect of accreted interstellar matter on the terrestrial environment. Mon not R Astron. Soc. 238, 1465–1478 (1989).
Meyer, D. M. et al. The remarkable high pressure of the local Leo cold cloud. Astrophys. J. 752, 119 (15pp) (2012).
Giacalone, J. et al. Anomalous cosmic rays and heliospheric energetic particles. Space Sci. Rev. 218, 22 (2022).
Giacalone, J. Large-scale hybrid simulations of particle acceleration at a parallel shock. Astrophys. J. 609, 452–458 (2004).
Leroy, M. M. et al. Simulation of a perpendicular bow shock. Geophys. Res. Lett. Vol. 8 (12), 1269 (1981).
Parker, E. N. The passage of energetic charged particles through interplanetary space. Planet. Space Sci. 13, 99–49 (1965).
Giacalone, J. & Jokipii, J. R. The longitudinal transport of energetic ions from impulsive solar flares in interplanetary space. Astrophys. J. 751 (5pp), L33 (2012).
Chen, X., Giacalone, J. & Guo, F. Solar energetic particle acceleration at a spherical shock with the shock normal angle theta-BN evolving in space and time. Astrophys. J. 941 (8), 23 (2022).
Giacalone, J. et al. Analyses of ∼0.05–2 MeV ions associated with the 2022 February 16 energetic storm particle event observed by Parker solar probe. Astrophys. J. 958, 144 (2023).
Chen, X., Giacalone, J., Guo, F. & Klein, K. G. Parallel diffusion coefficient of energetic charged particles in the inner heliosphere from the turbulent magnetic fields measured by Parker solar probe. Astrophys. J. 965, 61 (2024).
Giacalone, J. et al. Hybrid simulations of Interstellar Pickup Protons Accelerated at the Solar-Wind Termination Shock at Multiple Location, The Astrophysical Journal 911, Issue 1, id. 27, 8pp (2021).
Giacalone, J., Burgess, D., Schwartz, S. J. & Ellison, D. C. Ion injection and acceleration at parallel shocks: comparisons of Self-Consistent plasma simulations with existing theories. Astrophys. J. 402, 550–559 (1993).
Winske, D. & Omidi, N. A non-specialists’ guide to kinetic simulations of space plasmas. J. Geophys. Res. 101, 17287–17303 (1996).
Giacalone, J., Burgess, J., Schwartz, D., Ellison, S. J. & Bennett, D. C. Injection and acceleration of thermal protons at quasi-parallel shocks: A hybrid simulation parameter survey. J. Geophys. Res. 102, 19789–19804 (1997).
Mewaldt, R. A. et al. Proton, helium, and electron spectra during the large solar particle events of October–November 2003. J. Geophys. Research: Space Phys. 110 https://doi.org/10.1029/2005JA011038 (2005).
Quest, K. B. Theory and simulation of collisionless parallel shocks. J. Geophys. Res. 93, 9649–9680 (1988).
Jokipii, J. R. Particle acceleration at a termination shock: 1. Application to the solar wind and the anomalous component. J. Geophys. Res. 91, 2929 (1986).
Gosling, J. T., Asbrdge, J. R., Bame, S. J., Paschmann, G. & Sckopke, N. Observations of two distinct populations of bow shock ions in the upstream solar wind. Geophys. Res. Lett. 5, 957–970 (1978).
Ipavich, F. M., Gosling, J. T. & Scholer, M. Correlation between the He/H ratios in upstream particle events and in the solar wind. J. Geophys. Res. 89, 1501–1507 (1984).
Ellison, D. C. Shock acceleration of diffuse ions at the earth’s bow shock: acceleration efficiency and A/Z enhancements. J. Geophys. Res. 90, 29–38 (1985).
Gosling, J. T. et al. Interplanetary ions during an energetic storm particle event: The distribution function from solar wind thermal energies to 1.6 MeV. J. Geophys. Res. 86, 547 (1981).
Lario, D. et al. E. C. Evolution of the suprathermal proton population at interplanetary shocks, The Astronomical Journal 158, article id. 12 (2019).
Giacalone, J. Diffusive shock acceleration of high-energy charged particles at fast interplanetary shocks: a parameter survey. Astrophys. J. 799, articleid80–12pp (2015).
Florinski, V. & Pogorelov, N. V. Four-dimensional transport of galactic cosmic rays in the outer heliosphere and heliosheath. Astrophys. J. 701, 642–651 (2009).
Usoskin, I. G. et al. The AD775 cosmic event revisited: the sun is to blame. Astron. Astrophys. 552, L3 (4pp) (2013).
Usoskin, I. G. et al. Solar proton events in cosmogenic isotope data. Geophys. Res. Lett. 33 (4pp), L08107 (2006).
Miyake, F. et al. A signature of cosmic-ray increase in AS 774–775 from tree rings in Japan. Nature 486, 240–242 (2012).
Haud, U. Gaussian decomposition of H I surveys V. Search for very cold clouds. Astron. Astrophys. 514 (7pp), A27 (2010).
Vannier, H. et al. Mapping our path through the local interstellar medium: high-resolution ultraviolet absorption spectroscopy of sight lines along the sun’s historical trajectory. Astrophys. J. 981, 102 (2025).
Peek, J. et al. 245th Meeting of the American Astronomical Society, id. 174.08. Bulletin of the American Astronomical Society, 57: No. 2 e-id 2025n2i174p08 (2025).
Poluianov, S. V., Kovaltsov, G. A., Mishev, A. L. & Usoskin, I. G. Production of cosmogenic isotopes 7Be, 10Be, 14 C, 22Na, and Cl in the atmosphere: altitudinal profiles of yield functions. J. Geophys. Res. : Atmos. 121, 8125–8136 (2016).
Brehm, N. et al. Eleven-year solar cycles over the last millennium revealed by radio carbon in tree rings. Nat. Geosci. 14, 10 (2021).
Miyake, F. et al. A single-year cosmic ray event at 5410 BCE registered in 14 C of tree rings, Geophys. Res. Lett. 48, eGL093419 (2021). (2021).
Delaygue, G. & Bard, E. An Antarctic view of beryllium-10 and solar activity for the past millenium. Clim. Dyn. 36, 3301 (2011).
Frank, M. et al. A 200 Kyr record of cosmogenic radionuclide production rate and geomagnetic field intensity from 10Be in globally stacked deep-sea sediments. Earth Planet. Sci. Lett. 149, 121–129 (1997).
Nica, A., Opher, M., Miller, J. & Middleton, J. L. Modeling cosmogenic 10Be during the heliosphere’s encounter with an interstellar cold cloud. Geophys. Res. Lett. Rev. (2025).
Koll, D. et al. A cosmogenic 10Be anomaly during the late miocene as independent time marker for marine archives. Nat. Commun. 16, 866, 1 (2025).
Koll, D., Feige, J., Lachner, J. & Wallner, A. No indication for a strong increase in GCR intensity 2–3 Myr ago from cosmogenic nuclides, matter arising, (2025). Nature Astronomy in review.
Frank, M. et al. Beryllium isotopes in central Arctic ocean sediments over the past 12.3 million years: stratigraphic and paleoclimatic implications. Paleoceanography 23, PA1S02 (2008). (12 pp).
Opher, M. et al. Reply to No indication for a strong increase in GCR intensity 2–3 Myr ago from cosmogenic nuclides by Dominik Koll, Matter Arising, Nature Astronomy, in review (2025).
Usoskin, I. G. & Kovaltsov, A. Cosmic ray induced ionization in the atmosphere: full modeling and practical applications. J. Geophys. Res. 111 (9), D21206 (2006).
Nica, A., Opher, M., Miller, J. & Hatzaki, M. Impact of galactic cosmic rays on earth’s climate during an encounter with the local Lynx of cold clouds 2–3 Myr ago. J. Geophys. Research:Atmospheres. 130, e2025JD044084. https://doi.org/10.1029/2025JD044084 (2025).
Tanaka, H., Kono, M. & Uchimura, H. Some global features of paleointensity in geologic time. Geophys. J. Int. 120, 97–102 (1995).
Valet, J. P., Meynadier, L. & Guyodo, Y. Geomagnetic dipole strength and reversal rate over the past two million years. Nature 435, 802–805 (2005).
Ogg, J. G. Chapter 5- geomagnetic Polarity time scale. Geologic time Scale. 2020 1, 159–192 (2020).
Merill, R. T. & McFadden, P. L. Geomagnetic Polarity transitions. Rev. Geophys. 37, 201–226 (1999).
Knie, K. et al. Phys. Rev. Lett. 83: 18 (1999).
Melott, A. L., Thomas, B. C., Kacherlrieb, M., Semikoz, D. V. & Overholt, A. C. A supernova at 50pc: effects on the earth’s atmosphere and biota. Astrophys. J. 840 (9), 105 (2017).
Mironova, I. A. et al. Energetic particle influence on the earth’s atmosphere. Space Sci. Rev. 194, 1–96 (2015).
Rozanov, E., Calisto, M., Egorova, T. & Schmutz, W. Energetic particles, atmospheric chemistry, dynamics, climate, modeling. Surv. Geophys. 33 (Issue 3–4), 483–501 (2012).
Baumgaertner, A. J. G., Seppala, A., Jockel, P. & Clilverd, M. A. Geomagnetic activity related nox enhancements and Polar surface air temperature variability in a chemistry climate model: modulation of the NAM index. Atmos. Chem. Phys. 11, 4521–4531 (2011).
Hays, J. D., Imbrie, J. & Shackleton, N. J. Variations in the earth’s orbit: pacemaker of the ice ages: for 500,000 years, major Climatic changes have followed variations in obliquity and precession. Science 194, 1121–1132 (1976).
Gettelman, A. et al. The whole atmosphere community climate model version 6 (WACCM6). JGR 124, 12380–12403 (2019).
Hutchinson, F. Chemical changes induced in DNA by ionizing radiation. Prog. Nucl. Acid Res. Mol. Biol. 32, 115–154 (1985).
Cucinotta, F. & Durante, A. M. Cancer risk from exposure to galactic cosmic rays: implications for space exploration by human beings. Lancet Oncol. The. 7, 431–435 (2006).
Richardson, R. B. Ionizing radiation and aging: rejuvenating an old Idea. Aging 1, 887–902 (2009).
Edenhofer, G. et al. A parsec-scale galactic 3D dust map out to 1.25 Kpc from the sun. Astron. Astrophys. 685 (A82), 23pp (2024).
Acknowledgements
This work is supported by NASA grant 80NSSC22M0164, 18-DRIVE18_2-0029 as part of the NASA/DRIVE program titled “Our Heliospheric Shield”. For more information about this center please visit: https://shielddrivecenter.com/. EPE was supported by JSPS KAKENHI (24K01785).
Funding
This work is supported by NASA grant 80NSSC22M0164, 18-DRIVE18_2–0029 as part of the NASA/DRIVE program titled “Our Heliospheric Shield”. For more information about this center please visit: https://shielddrivecenter.com/. EPE was supported by JSPS KAKENHI (24K01785).
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Conceptualization: M.O., E.P.E. and A.L; Methodology: M. O. MHD code results; J.G. and A.C. estimation of the radiation; Interpretation and Conclusions, Writing: All authors were involved.
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Opher, M., Giacalone, J., Loeb, A. et al. Increased and varied radiation during the Sun’s encounters with cold clouds in the last 10 million years. Sci Rep (2026). https://doi.org/10.1038/s41598-026-36926-z
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DOI: https://doi.org/10.1038/s41598-026-36926-z
