> In 2020, NASA’s New Horizons spacecraft, having passed the orbit of Pluto, measured a proxy for the amount of hydrogen around it. In the area between stars in our galaxy — the “interstellar medium,” or ISM — New Horizons found around 130 hydrogen atoms per liter of space.

Not to nitpick, but I thought New Horizons hasn't entered the ISM, and only the Voyager craft have?