WASHINGTON - Scientists have discovered oxygen molecules in deep space in a region of the Orion nebula, some 1,500 light years from the Earth, the US National Aeronautics and Space Administration (NASA) announced Monday.

The discovery was made with European Space Agency's Herschel Space Observatory, which used large telescope and infrared detectors to find the elusive molecules.

Individual atoms of oxygen are common in space, particularly around massive stars. But, molecular oxygen, which makes up about 20 percent of the air we breathe, has eluded astronomers until now.

"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," said Paul Goldsmith, NASA's Herschel project scientist at the agency's Jet Propulsion Laboratory in Pasadena, California.

Goldsmith is lead author of a recent paper describing the findings in the Astrophysical Journal. Herschel is a European Space Agency-led mission with important NASA contributions.

The researchers plan to continue their hunt for oxygen molecules in other star-forming regions.

"Oxygen is the third most common element in the universe and its molecular form must be abundant in space," said Bill Danchi, Herschel program scientist at NASA Headquarters in Washington. " Herschel is proving a powerful tool to probe this unsolved mystery. The observatory gives astronomers an innovative tool to look at a whole new set of wavelengths where the tell-tale signature of oxygen may be hiding."