In 1977, NASA launched two spacecraft, Voyager 1 and 2, on a grand tour of the solar system and into the mysteries of interstellar space. Famously attached to each of these probes is the Voyager Golden Record containing a message for any extraterrestrial intelligence that might encounter it, perhaps billions of years from now. Voyager 1 entered interstellar space in 2012. Last year, Voyager 2 joined its twin beyond the heliosphere, described by NASA as "the protective bubble of particles and magnetic fields created by our Sun." Today sees the publication of several scientific papers analyzing the data that Voyager 2 has sent back since its crossing. Congratulations to the inspiring scientists and engineers behind these latest papers and the incredible Voyager mission, still going strong 40+ years later! From NASA:
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Each paper details the findings from one of Voyager 2's five operating science instruments: a magnetic field sensor, two instruments to detect energetic particles in different energy ranges and two instruments for studying plasma (a gas composed of charged particles). Taken together, the findings help paint a picture of this cosmic shoreline, where the environment created by our Sun ends and the vast ocean of interstellar space begins.
The Sun's heliosphere is like a ship sailing through interstellar space. Both the heliosphere and interstellar space are filled with plasma, a gas that has had some of its atoms stripped of their electrons. The plasma inside the heliosphere is hot and sparse, while the plasma in interstellar space is colder and denser.