Heliopause

Assembled from 25 blocks · 3 evidence · 9 related

1. Story
2. The outer boundary of the heliosphere: the surface where solar wind plasma gives way to interstellar plasma. It has no wall and no visible edge, so crossing it is detected by what the instruments stop and start seeing — a sharp drop in low-energy particles coming from the Sun, a simultaneous rise in galactic cosmic rays arriving from outside, and a jump in the density of the surrounding electrons. Voyager 1 crossed on 25 August 2012 at 121.6 AU; Voyager 2 crossed on 5 November 2018 at 119 AU. The confirmations came differently. Voyager 1's plasma instrument had failed in 1980, so the density had to be inferred from plasma oscillations recorded by the plasma wave subsystem — an electron oscillation near 2.6 kHz implying about 0.08 electrons per cubic centimetre, some forty times the density of the solar wind at that distance. Voyager 2 measured the plasma directly, and found a boundary layer about 1.5 AU thick before the crossing and a transition that took less than a day. Not a place.
3. Knowledge
4. Heliosphere
5. Heliopause
6. Very local interstellar medium
7. Connections
8. Very local interstellar medium
9. Heliosphere
10. Voyager 1 crosses the heliopause at 121.6 AU
11. The 2012 crossing is confirmed from plasma oscillations
12. Voyager 2 crosses the heliopause at 119 AU
13. Heliosphere
14. Heliopause
15. Voyager 1 crosses the heliopause at 121.6 AU
16. Voyager 2 crosses the heliopause at 119 AU
17. Very local interstellar medium
18. Solar wind
19. Termination shock
20. Heliopause
21. Voyager 2 crosses the termination shock at about 84 AU
22. Evidence
23. Voyager 1's plasma wave instrument recorded electron plasma oscillations near 2.6 kHz in October–November 2012 and April–May 2013, implying an electron density of about 0.08 cm⁻³ and indicating that the spacecraft had been in interstellar plasma continuously since the boundary crossings of July–August 2012, dated 25 August 2012 at 121.6 AU. V55 verification basis: the paper is on a publisher domain blocked to this session, but search results carried the frequency, the density and the crossing date and distance and attributed them to this paper.
24. Voyager 2 crossed the heliopause on 5 November 2018 at 119 AU; a boundary layer about 1.5 AU wide preceded it in which the plasma slowed, heated and was roughly twice as dense as typical heliosheath plasma; the transition took less than a day, and the interstellar plasma immediately outside was hotter than predicted, of order 30,000–50,000 °C against a prediction nearer 15,000–30,000 °C. V55 verification basis: the paper was not fetched — nature.com is blocked to this session — but search results carried these figures and attributed them to it.
25. NASA announced on 10 December 2018 that Voyager 2 had crossed the heliopause on 5 November 2018, confirmed by a sharp fall in solar wind particle intensity and a simultaneous rise in galactic cosmic rays measured by an instrument suite that, unlike Voyager 1's, included a working plasma science experiment. V55 verification basis: the release was not fetched; the substance is carried in search results attributing it to NASA and JPL.