The Extent of Solar Energetic Particle Irradiation in the Sun’s Protoplanetary Disk

The Extent of Solar Energetic Particle Irradiation in the Sun’s Protoplanetary Disk
Steven J. Desch, Ashley K. Herbst, Richard L. Hervig, Benjamin Jacobsen
arXiv:2512.03184v1 Announce Type: new
Abstract: Solar flares emit X rays and high-energy (MeV-GeV) ions (Solar Energetic Particles, or SEPs). Astronomical observations show solar mass-protostellar fluxes are a factor $Phi approx 3 times 10^2 – 3 times 10^3$ times higher than the present-day Sun. Constraining $Phi$ in the early solar system is important for modeling ionization in the Sun’s protoplanetary disk, the extent of magnetorotational instability or magnetocentrifugal outflows, or even production of short-lived radionuclides. Recent interpretations of meteoritic data — cosmogenic Ne in hibonite grains, initial $({}^{10}{rm Be}/{}^{9}{rm Be})_0$ ratios in Ca-rich, Al-rich inclusions (CAIs), or even inferences of live ${}^{7}{rm Be}$ in CAIs — have suggested values $Phi > 10^5$, even as large as $Phi approx 6 times 10^6$, which would make the young Sun extraordinarily active, even for a protostar. We constrain $Phi$ by re-examining these data. We conclude: cosmogenic Ne was produced in hibonite grains as they resided in the disk; ${}^{36}{rm Cl}$ was created in Cl-poor grains after the disk dissipated; ${}^{10}{rm Be}$ was inherited from the molecular cloud, with almost no ($ 5$ Myr of the solar nebula. The early Sun evidently emitted a flux of X rays and SEPs not atypical for a protostar.arXiv:2512.03184v1 Announce Type: new
Abstract: Solar flares emit X rays and high-energy (MeV-GeV) ions (Solar Energetic Particles, or SEPs). Astronomical observations show solar mass-protostellar fluxes are a factor $Phi approx 3 times 10^2 – 3 times 10^3$ times higher than the present-day Sun. Constraining $Phi$ in the early solar system is important for modeling ionization in the Sun’s protoplanetary disk, the extent of magnetorotational instability or magnetocentrifugal outflows, or even production of short-lived radionuclides. Recent interpretations of meteoritic data — cosmogenic Ne in hibonite grains, initial $({}^{10}{rm Be}/{}^{9}{rm Be})_0$ ratios in Ca-rich, Al-rich inclusions (CAIs), or even inferences of live ${}^{7}{rm Be}$ in CAIs — have suggested values $Phi > 10^5$, even as large as $Phi approx 6 times 10^6$, which would make the young Sun extraordinarily active, even for a protostar. We constrain $Phi$ by re-examining these data. We conclude: cosmogenic Ne was produced in hibonite grains as they resided in the disk; ${}^{36}{rm Cl}$ was created in Cl-poor grains after the disk dissipated; ${}^{10}{rm Be}$ was inherited from the molecular cloud, with almost no ($ 5$ Myr of the solar nebula. The early Sun evidently emitted a flux of X rays and SEPs not atypical for a protostar.