Voyager 2 Plasma Observations of the Heliopause and Interstellar Medium

The solar wind blows outward from the Sun and forms a bubble of solar material in the interstellar medium, the matter between the stars. The heliopause (HP) is the boundary that divides the hot tenuous solar wind plasma in the heliosheath from the cold dense very local interstellar medium (VLISM). The Voyager 2 (V2) plasma experiment observed the HP crossing from the solar wind into the VLISM on November 5, 2018 at 119 AU. The HP distance is only 3 AU closer at V2 than at V1 (119.0 verses 121.7 AU) despite the 10 AU difference in the termination shock distances at these two spacecraft (94 AU at V1 and 84 AU at V2). 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 the typical heliosheath plasma. A HP boundary layer begins about 0.06 AU ahead of 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. Models and observations predict a VLISM temperature of a 16,000 - 32,000 degrees K; V2 observations show the temperature is 30,000-50,000 degrees K.