Nature Astronomy ( IF 11.518 ) Pub Date : 2019-11-04 , DOI: 10.1038/s41550-019-0927-4 Stamatios M. Krimigis, Robert B. Decker, Edmond C. Roelof, Matthew E. Hill, Carl O. Bostrom, Konstantinos Dialynas, George Gloeckler, Douglas C. Hamilton, Edward P. Keath, Louis J. Lanzerotti
The long-anticipated encounter by Voyager 2 (V2) of the region between the heliosphere and the very local interstellar medium (VLISM) occurred toward the end of 2018. Here, we report measurements of energetic (>28 keV) charged particles on V2 from the interface region between the heliosheath, dominated by heated solar wind plasma, and the VLISM, expected to contain cold non-solar plasma and the Galactic magnetic field. The number of particles of solar origin began a gradual decrease on 7 August 2018 (118.2 au), while those of Galactic origin (Galactic cosmic rays) increased ~20% in number over a period of a few weeks. An abrupt change occurred on 5 November when V2 was located at 119 au, with a decrease in the number of particles at energies of >28 keV and a corresponding increase in the number of Galactic cosmic rays of energy E > 213 MeV. This signature of the transition to the VLISM resembles, but is very different from, that observed on Voyager 1 at ~121.6 au, associated with the putative crossing of the heliopause some six years earlier.