Modeling Cosmogenic 10Be During the Heliosphere's Encounter with an Interstellar Cold Cloud

TL;DR

The paper addresses whether cosmogenic $^{10}\text{Be}$ records can reveal past heliosphere compressions as the Sun traversed interstellar cold clouds. It develops a CRAC-based atmospheric cascade model to predict $^{10}\text{Be}$ production under two cloud-crossing geometries and multiple durations, incorporating interstellar GCRs and heliospheric energetic particles. The findings show that GCRs outside a compressed heliosphere yield modest Be increases, whereas HEPs can boost Be production by up to about $270\times$ at the poles and $70\times$ globally, depending on exposure fractions, with detectability strongly tied to event duration and archive resolution. The results provide a quantitative framework for interpreting Be records in marine archives and identifying which archive types are best suited to detect different cloud-crossing scenarios.

Abstract

Geologic records of cosmogenic 10Be are sensitive to changes in the radiation environment with time. Recent works suggest there are periods when the Sun encountered massive cold clouds which compressed the heliosphere to within Earth's orbit. This would expose Earth to increased galactic cosmic rays and MeV-energy particles of heliospheric origin. We model 10Be production in Earth's atmosphere during possible cold cloud encounters, and estimate their detectability in marine records of variable temporal resolution. We find that an AU-scale cold cloud encounter can be detected using ocean sediment measurements of 10Be if Earth spends time inside the compressed heliosphere. For typical relative speeds between the Sun and local interstellar clouds, this translates to a crossing time of ~100 years. A cloud must have an extension on the scale of parsecs to tens-of-parsecs (crossing time 0.1-1 Myr) to be detectable through 10Be measurements in iron-manganese crusts.

Figures (4)

• Figure 1: Cartoon diagram showing compression of the heliosphere and Earth's exposure to energetic particles as the Solar System intersects an interstellar cold cloud. Panel a shows heliospheric compression following a collision with a cold cloud in the ecliptic plane, from an edge-on and top-down view. Earth's orbit dips in and out of the heliosphere, exposing Earth to interstellar GCRs while it is outside the heliosphere and to HEPs inside the heliosphere. Panel b shows heliospheric compression if the cloud's relative velocity is perpendicular to the ecliptic plane. In this case, the heliosphere may be compressed within Earth’s orbit, and Earth would only be exposed to interstellar GCRs.
• Figure 2: Proton differential energy spectra of the heliospheric energetic particle (HEP) flux as shown by opher_heliospheric_2025 and applied fit function (blue line), interstellar flux of GCRs (black line), GCRs modulated for typical solar minimum conditions (purple line), and typical solar maximum conditions (pink line). Black circles represent cosmic ray detections from Voyager 1 after exiting the heliosphere, from DOY 342 of 2012 to DOY 181 of 2015. Purple points represent data from a BESS balloon flight in 1997 and from IMP8 in 1996. These data are shown as in cummings_galactic_2016. Navy squares show SEP fluxes during the Halloween Storm of 2003, one of the largest recorded solar storms mewaldt_proton_2005.
• Figure 3: Simulated $^{10}\text{Be}$ signal during an ecliptic collision with a cold cloud (Figure 1a). We consider cloud crossing times between $10^2$ years and $10^6$ years. Turquoise lines show the modeled $^{10}\text{Be}$ production rate over time from 80% GCRs and 20% HEPs, and blue points show simulated measurements in ocean sediments (left, time resolution=1 kyr) and iron-manganese crusts (right, time resolution=0.5 Myr) based on the modeled production rates. Dashed gray lines show the upper range of typical variability in $^{10}\text{Be}$ recorded in marine archives due to dynamic terrestrial processes willenbring_long-term_2010simon_increased_2018middleton_oceanographic_2025.
• Figure 4: Similar to Figure \ref{['fig:10Be_time_avg']}, but for a perpendicular collision with a cold cloud (Figure \ref{['fig:heliosphere']}b). Before the cold cloud crossing, the $^{10}\text{Be}$ production rate is set to the average modulation of GCRs throughout the solar cycle. During the crossing, the $^{10}\text{Be}$ production rate is induced by the interstellar flux of GCRs.