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helium 1083nm line

(helium 1080nm line)
(helium line viewable through atmospheric windows)

The helium 1083nm line (sometimes referred to as the helium 1080nm line) is a line triplet (i.e., three fine structure lines) of helium in a metastable state. It is a near infrared line but within optical atmospheric window, and little affected by the interstellar medium, thus useful for ground observation. Thin helium surrounding an extra-solar planet undergoing atmospheric escape can create the right conditions to generate an absorption line detectable through transmission spectroscopy.