Molecules of oxygen have been found in the nearby Orion star-forming complex, the first undisputed detection of oxygen molecules in space.   Previous missions looking for the molecular variety, two atoms of oxygen bonded together, had been fruitless.

Yet as interesting as the discovery is, it leads to a bigger question; the observed amount of atomic oxygen is far less than expected.  Where is all the oxygen hiding in the cold clouds?

Dark oxygen, anyone?

Maybe, but the more likely answer is that oxygen atoms freeze onto tiny dust grains found floating in space and are converted to water ice, effectively removing them from sight.   If this is true, the ice should evaporate in warmer regions of the cosmos, returning water to the gas and allowing molecular oxygen to form and to be seen.  

Oxygen molecules found in Orion

The new image from Herschel offers a peek inside a 'cavern' of dust and gas where thousands of stars are forming. The image, taken by the Advanced Camera for Surveys (ACS) aboard NASA's Hubble Space Telescope, represents the sharpest view ever taken of this region, called the Orion Nebula,1500 light-years away and the nearest star-forming region to Earth.  More than 3000 stars of various sizes appear in this image. Some of them have never been seen in visible light   Astronomers used 520 Hubble images, taken in five colors, to make this picture. They also added ground-based photos to fill out the nebula. The ACS mosaic covers approximately the apparent angular size of the full Moon. These observations were taken between 2004 and 2005. Photo: NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team)

Paul Goldsmith, NASA's Herschel project scientist at NASA's Jet Propulsion Laboratory, Pasadena, California, and an international team of investigators went looking for it with Herschel.

They used Herschel's HIFI far-infrared instrument and targeted Orion, where they reasoned that the forming stars would heat the surrounding gas and dust.

Using three infrared frequencies of the instrument, the Herschel Oxygen Project team were successful. They found there to be one molecule of oxygen for every million hydrogen molecules.

"This explains where some of the oxygen might be hiding," said Dr 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."

Oxygen, in all its forms, is the third most abundant element in the Universe and a major ingredient of our planet. It is found in our atmosphere, oceans and rocks, and is critical for life itself because we breathe the molecular form.

Although the search continues for it in space, Göran Pilbratt, ESA's Herschel Project Scientist, believes this is a breakthrough moment: "Thanks to Herschel, we now have an undisputed confirmation that molecular oxygen is definitely out there. There are still many open questions but Herschel's superior capabilities now enables us to address these riddles."