Class 17 nebula
A class 17 nebula was a type of nebula containing hydrogen and helium. It was considered a gaseous anomaly.

In 2373, the  encountered a class 17 nebula in the Delta Quadrant containing 7,000 parts per million of sirillium. It was somewhat similar in composition to the class 11 Azure Nebula near Klingon space in the Beta Quadrant. ()

de:Klasse-17-Nebel
ja:クラス17星雲
nl:Klasse 17 nevel
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Class 17 nebula