Voyager 2 enters interstellar space

摘要

As the solar wind continuouslyblows away from the Sun atsupersonic speeds, it creates acavity in interstellar space filled with solarmaterial — the heliosphere. Because thesolar and interstellar plasmas have differentcompositions, densities, temperatures, andare braided by magnetic fields with differentorigins, they cannot interact freely and mustbe separated by a discontinuous boundary.This outer edge of the heliosphere is calledthe heliopause and marks the start ofinterstellar space, or rather, the start of theinterstellar medium (Fig. 1). The Voyager1 spacecraft, launched in 1977 shortly afterits partner Voyager 2, made the transitionthrough the heliopause seven years ago.Now Voyager 2 has also completed thisastonishing feat and data from several of itsinstruments taken during the crossing arereported in a series of papers1–5 in this issueof Nature Astronomy.