Magnetic field and particle measurements made by Voyager 2 at and near the heliopause

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Abstract

The heliopause is a boundary that separates the heliosheath (which contains magnetic fields and plasmas that originate in the Sun) from the interstellar medium (which contains magnetic fields and particles of stellar/interstellar origin). Observations of the heliopause were first made by the particles and fields instruments on the Voyager 1 spacecraft, moving radially in the northern hemisphere, which crossed the heliopause on 25 August 2012 at a distance of 121.6 au. We show using observations of the magnetic field and energetic particles that Voyager 2 crossed the heliopause in the southern hemisphere on 5 November 2018 at a distance of ≈119.0 au. Voyager 2 observed a much thinner and simpler heliopause than Voyager 1 as well as stronger interstellar magnetic fields, and it discovered a ‘magnetic barrier’ in the heliosheath adjacent to the heliopause that strongly influences the entry of cosmic rays into the heliosphere. The magnetic field direction observed by Voyager 2 changed smoothly from the time of arrival at the magnetic barrier, through it, and onwards into the interstellar medium, with a small (a few degrees) or no change across the heliopause. These observations, together with the Voyager 1 observations and existing models, show that the magnetic barrier, the heliopause and the neighbouring very local interstellar medium form a complex interconnected dynamical system.

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Fig. 1: The heliopause crossing observed by Voyager 2 in the measurements of the magnetic field and the >0.5 MeV nucleon–1 energetic particles.
Fig. 2: The heliopause crossing of Voyager 2 and the neighbouring heliosheath and VLISM in terms of the temporal variation of B, λ and δ.
Fig. 3: The RTN components of B and the magnitude of B as a function of time just before and after the heliopause crossing of Voyager 2.
Fig. 4: The magnetic field and plasma in the outer heliosheath, the magnetic barrier and the VLISM, as measured by Voyager 2.
Fig. 5: Magnetic field strength B in the plane containing the trajectories of Voyager 1 and Voyager 2.
Fig. 6: The relationship between the magnetic barrier and cosmic rays, and the variation of the magnetic field direction across the heliopause.

Data availability

The 48 s averages of the magnetic field data are posted on NASA’s Space Science Data Facility (SPDF) CDAWeb site: https://cdaweb.gsfc.nasa.gov/index.html/. The hour averages of the magnetic field data are posted on NASA’s Space Science Data Facility (SPDF) COHOWeb site https://omniweb.sci.gsfc.nasa.gov/coho/.

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Acknowledgements

L.F.B., N.F.N., D.B.B., J.P., L.K.J. and A.S. were supported by the NASA Voyager Project to the NASA/GSFC Magnetometer Team under internal NASA funding. L.K.J. is grateful for support from The International Space Science Institute in Bern in the framework of the team ‘The Physics of the Very Local Interstellar Medium’. L.F.B. thanks N. Pogorelov and H. Washimi for helpful discussions, and N. Pogorelov for preparing Fig. 5. J.D.R. was supported by NASA under grant number 959203 from the Jet Propulsion Laboratory to the Massachusetts Institute.

Author information

L.F.B. wrote the initial draft of the manuscript, incorporated contributions from the other authors, compiled and submitted the final paper, prepared the final edited datasets, and submitted the data to the NASA archives. N.F.N. is the principal investigator of the magnetic field investigation. D.B.B. calibrated the magnetic field data. J.P. and L.K.J. assisted in data calibrations and made contributions to the paper. A.S. managed the data processing and the budget. J.D.R. provided the plasma data and contributed to their interpretation. E.C.S. provided the cosmic ray data and >0.5 MeV data and contributed to the interpretation of the data.

Correspondence to L. F. Burlaga.

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Burlaga, L.F., Ness, N.F., Berdichevsky, D.B. et al. Magnetic field and particle measurements made by Voyager 2 at and near the heliopause. Nat Astron 3, 1007–1012 (2019) doi:10.1038/s41550-019-0920-y

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