Publication: A possible direct exposure of the Earth to the cold dense interstellar medium 2–3 Myr ago
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2024-06-10
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Springer Science and Business Media LLC
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Opher, M., Loeb, A. & Peek, J.E.G. A possible direct exposure of the Earth to the cold dense interstellar medium 2–3 Myr ago. Nat Astron (2024). https://doi.org/10.1038/s41550-024-02279-8
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Abstract
Cold interstellar medium (ISM) clouds, 4-5 order of magnitude denser than the diffuse ISM, exist in the galaxy and our Solar System has most likely encountered at least one of them during its lifetime. However, evidence for such an encounter [[and its effects]] have not been studied in detail yet. Here we derive the velocity field of the Local Ribbon of Cold Clouds (LRCC) by modelling the 21-cm data from the HI4PI survey and find that the Solar System may have passed through the LRCC in the constellation Lynx between 2-3 million years ago. Using a state-of-the-art simulation of the heliosphere, we show that during the passage the heliosphere had shrunk to a scale of 0.22AU, smaller than the Earth’s orbit around the Sun. This would have put the Earth in direct contact with the dense ISM for a period of time and exposed it to a neutral hydrogen density above 3000cm-3. Such a scenario agrees with geological evidence from 60Fe and 244Pu isotopes. The encounter and related increased radiation from galactic cosmic rays flux might have had substantial impact on the Earth system and climate.