Voyager 1 and Voyager 2 launched by the United States in 1977 are the farthest probes for human flight. They completed the heliospheric crossing in August of 20 12 and June of 2010/year respectively.
Voyager 1 passes through the top of the heliosphere at the position north of the earth's orbital plane (ecliptic plane), and the distance from the sun is 12 1.7 astronomical unit. Voyager 2 passes through the top of the heliosphere from the south of the ecliptic, at a distance of 1 19.0 astronomical units from the sun. Because some of the plasma spectrometers on Voyager 2 are still working normally, unlike those on Voyager 1 in the 1980s, scientists have placed greater expectations on the scientific discoveries that Voyager 2' s interplanetary voyage can bring.
In the paper on plasma density observation, scientists found that the method of estimating electron density through electromagnetic field fluctuation is reliable. According to the observation data of Voyager 2, the electron density directly measured by plasma spectrometer is basically consistent with the electron density estimated by electromagnetic wave fluctuation. At the same time, the density of interstellar matter detected by Voyager 2 and Voyager 1 is basically the same, which further confirms the theoretical calculation result that the density will cross the heliosphere 20-50 times.
Scientists showed two galactic cosmic ray enhancement events that Voyager 1 encountered in the heliosphere. Just like heartbeat pulses, these two enhancements show occasional short-term rapid changes. Voyager 2 did not encounter such an event in the heliosphere, but the characteristics of cosmic rays observed outside the heliosphere were consistent with the two enhancement events that Voyager 1 encountered in the heliosphere. This shows that cosmic rays may penetrate the magnetic field barrier through some mechanism and may invade the heliosphere in a small amount in a short time.
Voyager 2 is located near the top of the heliosphere, and its normal plasma spectrometer allows scientists to discover two boundary layers. The first boundary layer is inward and thick, 1.5 astronomical unit. When plasma gallops from the surface of the sun to the top of the heliosphere, the density and temperature of the boundary layer begin to increase. Near the top of the solar layer, in another boundary layer with a thickness of only 0.06 astronomical unit, the speed of plasma leaving the sun shows a downward trend. This is different from what was observed on Voyager 1. Voyager 1 observed that the plasma stagnated before reaching the top of the heliosphere, while Voyager 2 observed that the plasma kept a high forward posture until reaching the second boundary layer.