One of astronomy's longest-running "missing persons" investigations has concluded: astronomers have found molecular oxygen in space.
While single atoms of oxygen have been found alone or incorporated into other molecules, the oxygen molecule - the one we breathe - had never been seen.
The Herschel space telescope spotted the molecules in a star-forming region in the constellation of Orion.
The find will be published in the Astrophysical Journal.
Oxygen is the third most abundant element in the cosmos, after hydrogen and helium. Its molecular form, with two atoms joined by a double bond, makes life on Earth possible - but this form had never definitively been seen in space.
A 2007 effort from the Swedish Odin telescope, published in the journal Astronomy and Astrophysics, claimed a discovery of oxygen in a nearby star-forming region, but the discovery could not be independently confirmed.
One possible location for the missing oxygen is locked onto dust grains and incorporated into water ice.
The team chose a star-forming region in the constellation Orion, believing that oxygen would be "baked off" from the ice and dust in a warmer, more turbulent part of space.
Instruments on the Herschel telescope, sensitive to infrared light, picked up small signatures of the elusive molecular oxygen.
"This explains where some of the oxygen might be hiding," said Paul Goldsmith, principal investigator on the Herschel Oxygen Project.
"But we didn't find large amounts of it, and still don't understand what is so special about the spots where we find it. The Universe still holds many secrets."