The heliopause is the theoretical boundary where the Sun's solar wind is stopped by the interstellar medium; where the solar wind's strength is no longer great enough to push back the stellar winds of the surrounding stars.
This is the boundary where the interstellar medium and solar wind pressures balance.
The crossing of the heliopause should be signaled by a sharp drop in the temperature of solar wind charged particles, a change in the direction of the magnetic field, and an increase in the number of galactic cosmic rays.
In May 2012, Voyager 1 detected a rapid increase in such cosmic rays (a 9% increase in a month, following a more gradual increase of 25% from Jan. 2009 to Jan. 2012), suggesting it was approaching the heliopause.
Between late August and early September 2012, Voyager 1 witnessed a sharp drop in protons from the sun, from 25 particles per second in late August, to about 2 particles per second by early October.
In September 2013, NASA announced that Voyager 1 had crossed the heliopause as of 25 August 2012.
This was at a distance of 121 AU (18 billion km) from the Sun.
Contrary to predictions, data from Voyager 1 indicates the magnetic field of the galaxy is aligned with the solar magnetic field.
The heliopause is the theoretical boundary where the Sun's solar wind is stopped by the interstellar medium; where the solar wind's strength is no longer great enough to push back the stellar winds of the surrounding stars. This is the boundary where the interstellar medium and solar wind pressures balance. The crossing of the heliopause should be signaled by a sharp drop in the temperature of solar wind charged particles, a change in the direction of the magnetic field, and an increase in the number of galactic cosmic rays. In May 2012, Voyager 1 detected a rapid increase in such cosmic rays (a 9% increase in a month, following a more gradual increase of 25% from Jan. 2009 to Jan. 2012), suggesting it was approaching the heliopause. Between late August and early September 2012, Voyager 1 witnessed a sharp drop in protons from the sun, from 25 particles per second in late August, to about 2 particles per second by early October. In September 2013, NASA announced that Voyager 1 had crossed the heliopause as of 25 August 2012. This was at a distance of 121 AU (18 billion km) from the Sun. Contrary to predictions, data from Voyager 1 indicates the magnetic field of the galaxy is aligned with the solar magnetic field.
Heliosphere