I’m finding that things I learn about are easier to remember if I either talk about them or write about them, so here’s something I learned today about the journey of my favourite spacecraft, the brothers Voyager.
On December 16, 2004, Voyager 1, 27 years and millions of miles away from the planet and the people that sent it on its exploratory journey, crossed the termination shock, officially leaving our Solar System and entering Interstellar space (Maybe. The line between the Solar System and Interstellar space is a little bit fuzzy because there’s a few ways to define it). Termination shock is where the charged particles of solar wind slow down so much as to be slower than the speed of sound. At this point in space, the particles begin to smoosh together, and from this they produce heat and twist around the sun’s magnetic field, which is carried this far by the solar wind. Voyager 2 passed through the termination shock three years after its younger brother (Voyager 1 was launched after Voyager 2).
Termination shock is not technically the border between the Solar System and interstellar space. From what I understand, that definition is given to the Heliopause, the line where the plasma of interstellar space finally overpowers the solar wind of the Sun. Where the solar wind is slowed down at the termination point, it is stopped in its tracks at the heliopause. Voyager 1 passed through the heliopause on August 25, 2012.
Sources/Expanded Reading:
https://voyager.jpl.nasa.gov/mission/timeline/#event-voyager-1-crosses-the-shock
http://ibex.swri.edu/students/What_is_the_termination.shtml
https://spaceplace.nasa.gov/interstellar/en/
https://www.jpl.nasa.gov/news/news.php?release=2013-278
https://en.wikipedia.org/wiki/Heliosphere