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Global heliospheric termination shock strength in the solar-interstellar interaction
E J Zirnstein1, R Kumar2, B L Shrestha1
1Department of Astrophysical Sciences, Princeton University, Princeton, NJ USA.
Nature Astronomy
|October 20, 2025
Summary
The heliospheric termination shock (HTS) strength varies globally. Higher polar compression occurs during solar minimum, influenced by solar wind dynamics and interstellar medium interactions.
Area of Science:
- Space Physics
- Heliophysics
- Plasma Physics
Background:
- The heliospheric termination shock (HTS) is a critical boundary where solar wind (SW) is compressed and heated before entering the interstellar medium.
- Global HTS properties are poorly understood due to limited in situ measurements, primarily from the Voyager spacecraft in only two directions.
- HTS-accelerated particles play a key role in the pressure balance between the heliosphere and the interstellar medium.
Purpose of the Study:
- To determine the global properties and strength of the heliospheric termination shock (HTS).
- To investigate the variations in HTS compression and their relationship with solar activity and solar wind conditions.
Main Methods:
- Utilized particle-in-cell, test particle, and magnetohydrodynamic simulations to model the HTS.
- Constrained simulation results using observational data from the Interstellar Boundary Explorer (IBEX) mission, specifically energetic neutral atoms.
- Analyzed energetic neutral atom data to infer HTS strength and characteristics.
Main Results:
- Revealed higher compression near the poles during solar minimum compared to solar maximum, linked to higher Mach number SW flow.
- Identified north-south asymmetries in HTS strength attributed to the evolution of polar coronal holes.
- Observed minimum compression near the heliospheric flanks, likely caused by solar wind slowing due to mass loading over extended distances.
Conclusions:
- The HTS strength exhibits significant global variations, with distinct differences between polar and flank regions.
- Solar minimum conditions lead to enhanced polar compression at the HTS.
- A strong correlation exists between HTS strength and the dynamics of the solar wind and the interstellar medium.
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