A molecular-hydrogen cloud only 300 light-years away spans roughly 40 full-Moon widths across our sky, yet astronomers did not identify it until 2025. Named Eos, it escaped conventional surveys becaus
Astronomers have identified a massive molecular-hydrogen cloud named Eos, located approximately 300 light-years away, which had previously escaped detection due to its unique composition. The discovery highlights the limitations of traditional carbon-monoxide surveys in mapping interstellar structures.
Why it matters
This discovery challenges existing astronomical survey methods and expands our understanding of the local interstellar medium.
Eos covers about 20 degrees of sky, but almost all its estimated 3,400 solar masses of molecular hydrogen escaped the carbon-monoxide surveys normally used to find such clouds.
Published September 13, 2026 · How we edit
One of the nearest molecular clouds to the Sun hid across a patch of sky about 20 degrees wide. That is roughly 40 times the apparent diameter of the full Moon. It was not identified until a 2025 study looked for molecular hydrogen in a way that most cloud surveys do not.
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