Oxygen molecules have been detected for the first ever time in space, helping explain where some of the universe's missing oxygen may be hiding.
While individual atoms of oxygen are common in space, particularly around massive stars, molecular oxygen - O2 - has never before been found. But it's the third most common element in the universe
The Herschel Space Observatory's large telescope and infrared detectors detected the molecules in the Orion star-forming complex.
"Oxygen gas was discovered in the 1770s, but it's taken us more than 230 years to finally say with certainty that this very simple molecule exists in space," says Paul Goldsmith, NASA's Herschel project scientist.
For decades, astronomers searched for oxygen molecules in space for using balloons, as well as ground- and space-based telescopes. The Swedish Odin telescope appeared to have found some in 2007, but the observation couldn't be confirmed.
Goldsmith and his colleagues believe that oxygen may be locked up in water ice, coating tiny dust grains. The oxygen they've found in the Orion nebula, they suggest, was formed after starlight warmed the icy grains, releasing water. This was converted into oxygen molecules.
It's a similar process to that believed to have caused the formation of hydrogen peroxide in space, as was observed earlier this month.
"This explains where some of the oxygen might be hiding," says Goldsmith. "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."
The researchers plan to look for more in other star-forming regions.