Extreme Solar Particle Ejection Event in the Last Few Million Years from Asteroid Itokawa Sample
Unusual explosive activity occasionally occurs from the Sun, releasing large amounts of solar energetic particles. Extreme solar particle ejection events in the past 11,000 yr have been detected by sharp increases of cosmogenic isotopes in annual tree rings and ice cores. However, quantitative estim...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/ad9919 |
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| Summary: | Unusual explosive activity occasionally occurs from the Sun, releasing large amounts of solar energetic particles. Extreme solar particle ejection events in the past 11,000 yr have been detected by sharp increases of cosmogenic isotopes in annual tree rings and ice cores. However, quantitative estimation of the event magnitudes is not straightforward, as the cosmogenic isotopes are indirect records of solar particles. Similar solar particle ejection events may also accumulate records in surface materials of airless bodies such as the Moon and asteroids. Samples from the asteroid 25143 Itokawa have been irradiated by solar winds for tens to hundreds of years at some points in the last few million years. Here, we report implantation profiles of solar particle He from an Itokawa regolith grain that trace an extreme solar particle ejection event. The implantation profiles indicate that the fluences of suprathermal solar particles were 250–1300 times larger than that expected from the current normal solar activity. Since the degrees of excesses are inversely related to the solar wind irradiation periods, the high-energy particle fluence would have been derived from a single event. The event was approximately 40 times larger than the 2003 Halloween solar storms, which is one of the largest solar particle ejection events observed since the space-based measurement of solar activity began. The event magnitude is similar to the largest events inferred from the cosmogenic isotope records in terrestrial samples. Our result provides direct evidence of an extreme solar particle ejection event in the last few million years. |
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| ISSN: | 1538-4357 |