The solar wind blows outwards from the Sun and forms a bubble of solar material in the interstellar medium. The heliopause (HP) is the boundary that divides the hot tenuous solar wind plasma in the heliosheath from the colder, denser very local interstellar medium (VLISM). The Voyager 2 plasma experiment observed the HP crossing from the solar wind into the VLISM on 5 November 2018 at 119 au. Here we present the first measurements of plasma at and near the HP and in the VLISM. A plasma boundary region with a width of 1.5 au is observed before the HP. The plasma in the boundary region slows, heats up and is twice as dense as typical heliosheath plasma. A much thinner boundary layer begins about 0.06 au inside the HP where the radial speed decreases and the density and magnetic field increase. The HP transition occurs in less than one day. The VLISM is variable near the HP and hotter than expected. Voyager 2 observations show that the temperature is 30,000–50,000 K, whereas models and observations predicted a VLISM temperature of 15,000–30,000 K.
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Data from the Voyager Plasma experiment are available at http://web.mit.edu/space/www/voyager.html
Burlaga, L. F. et al. Magnetic field observations as Voyager 1 entered the heliosheath depletion region. Science 341, 147–150 (2013).
Gurnett, D. A., Kurth, W. S., Burlaga, L. F. & Ness, N. F. In situ observations of interstellar plasma with Voyager 1. Science 341, 1489–1492 (2013).
Krimigis, S. M. et al. Search for the exit: Voyager 1 at heliosphere’s border with the galaxy. Science 341, 144–147 (2013).
Stone, E. C. et al. Voyager 1 observes low-energy galactic cosmic rays in a region depleted of heliospheric ions. Science 341, 150–153 (2013).
Stone, E. C., Cummings, A. C., Heikkila, B. C. & Lal, N. Cosmic ray measurements from Voyager 2 as it crossed into interstellar space. Nat. Astron. https://doi.org/10.1038/s41550-019-0928-3 (2019).
Krimigis, S. M. et al. Energetic charged particle measurements from Voyager 2 at the heliopause and beyond. Nat. Astron. https://doi.org/10.1038/s41550-019-0927-4 (2019).
Burlaga, L. F. et al. Magnetic field and particle measurements made by Voyager 2 at and near the heliopause. Nat. Astron. https://doi.org/10.1038/s41550-019-0920-y (2019).
Gurnett, D. A. & Kurth, W. S. Plasma densities near and beyond the heliopause from the Voyager 1 and 2 plasma wave instruments. Nat. Astron. https://doi.org/10.1038/s41550-019-0918-5 (2019).
Bridge, H. S. et al. The plasma experiment on the 1977 Voyager mission. Space Sci. Rev. 21, 259–287 (1977).
Richardson, J. D. et al. Cool heliosheath plasma and deceleration of the upstream solar wind at the termination shock. Nature 464, 63–65 (2008).
Krimigis, S. M., Roelof, E. C., Decker, R. B. & Hill, M. E. Zero outward flow velocity for plasma in a heliosheath transition layer. Nature 474, 359–361 (2011).
Burlaga, L. F., Ness, N. F. & Richardson, J. D. Transition from the unipolar region to the sector zone: Voyager 2, 2013 and 2014. Astrophys J. 841, 47–59 (2017).
Richardson, J. D. et al. Pressure pulses at Voyager 2: drivers of interstellar transients? Astrophys. J. 834, 190–195 (2017).
Decker, R. B., Krimigis, S. M., Roelof, R. B. & Hill, M. E. No meridional plasma flow in the heliosheath transition region. Nature 489, 124–127 (2012).
Stone, E. C. & Cummings, A. C. Cosmic rays in the heliosheath. Proc. Int. Cosmic Ray Conf. Beijing 12, 29–32 (2012).
Gurnett, D. A. et al. Precursors to interstellar shocks of solar origin. Astrophys. J. 809, 121–130 (2015).
McComas, D. J. et al. Local interstellar medium: Six years of direct sampling by IBEX. Astrophys. J. Suppl. Ser. 220, 22–32 (2015).
Zank, G. Interaction of the solar wind with the local interstellar medium: a theoretical perspective. Space Sci. Rev. 89, 413–688 (1999).
Fuselier, S. A. & Cairns, I. H. Reconnection at the heliopause: predictions for Voyager 2. J. Phys.Conf. Ser. 900, 012007 (2017).
Barnett, A. & Olbert, S. Response function of modulated grid Faraday cup plasma instruments. Rev. Sci. Instrum. 57, 2432–2440 (1986).
Richardson, J. D. & Decker, R. B. Voyager 2 observations of plasmas and flows out to 104 AU. Astrophys. J. 792, 126–130 (2014).
The work at MIT is supported by NASA. Magnetic field and GCR data are shown courtesy of the Voyager Magnetometer (N. Ness, P.I.) and Cosmic Ray Subsystem (E. Stone, P.I.) teams. We thank G. S. Gordon Jr and L. A. Finck for development of, and assistance with, the plasma analysis.
The authors declare no competing interests.
Peer review information Nature Astronomy thanks George Livadiotis, Brian Wood and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Richardson, J.D., Belcher, J.W., Garcia-Galindo, P. et al. Voyager 2 plasma observations of the heliopause and interstellar medium. Nat Astron 3, 1019–1023 (2019). https://doi.org/10.1038/s41550-019-0929-2
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