Part of the book: Astrophysics
Voyager 1 has now been beyond the heliopause for over 5 years since its seminal crossing of this boundary in August of 2012. During its epic 40 year journey of ~122 AU out to this boundary and beyond this spacecraft has passed through several regions of the heliosphere including the heliosheath of extent ~30 AU just inside the heliopause (HP), where extremely large and variable intensities of protons, helium and oxygen nuclei as well as electrons between 1 and 100 MeV were observed. Then, suddenly these particles completely vanished and new and completely different spectra of particles between 1 MeV up to ~1 GeV and beyond, instantly recognizable as those for galactic cosmic rays were observed. These spectra and intensities at all energies have remained constant to within ±1% for 5 years corresponding to 20 AU beyond the HP.
Part of the book: Cosmic Rays