AI Insight
NASA's New Horizons spacecraft, after passing Pluto's orbit, measured the density of hydrogen atoms in the interstellar medium and found approximately 130 hydrogen atoms per liter of space. This measurement challenges the common perception of interstellar space as empty, revealing instead a thin but measurable fog of neutral hydrogen and other atoms. The findings provide new data about the composition of the space between stars in our galaxy.
Why it matters
Understanding the density and distribution of hydrogen in interstellar space is crucial for models of galactic structure, star formation, and how matter is distributed throughout the Milky Way. These measurements from beyond Pluto's orbit offer a unique vantage point that cannot be replicated from Earth-based observations due to interference from the solar system's own hydrogen.
Understand the Science
You might imagine space to be empty. But the seeming void contains a barely perceptible fog of hydrogen and other neutral atoms. 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.
Source: A New Map of ‘Empty’ Space Challenges a Tranquil Picture of the Galaxy