How life molecules formed or got to our planet is still a mystery, but astronomers may have worked out the origin of the simplest organic molecules – they are put together by starlight.

An international team of researchers discovered that the powerful ultraviolet (UV) light from young stars is responsible for the formation of carbon ions (C+), carbon-hydrogen ions (CH+), and methylidyne molecules (CH), which are the first steps to forming more complex molecules.

A study describing the findings is published in the Astrophysical Journal.

"This is the initiation of the whole carbon chemistry. If you want to form anything more complicated, it goes through that pathway," said study co-author John Pearson, a researcher at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, in a statement.

"It's still a mystery how certain molecules get excited in the cores of galaxies. Our study is a clue that ultraviolet light from massive stars could be driving the excitation of molecules there, too."

In their paper, the scientists mapped the motion, temperature and amount of simple carbon ions and molecules in the Orion Nebula.

The presence of these compounds has been known since the 1940s when CH and CH+ were first observed in interstellar space, especially in giant molecular clouds where stars are born. It was clear that organic compounds must be linked with the formation of stars, but it wasn’t obvious how these molecules came to be.

A leading hypothesis suggested that these simple molecules were caused by "shocks" in these gas clouds. Young stars spit out loads of material and supernovae thrust plasma at high speed producing turbulence in the clouds.

^{The emission from ionized carbon atoms (in yellow) is overlaid on this image from the Herschel telescope. ESA/NASA/JPL-Caltech}

Using the European Space Agency's Herschel telescope, the team was able to look in incredible detail into the Orion Nebula. The discovered that the distribution of CH+ is not closely related to the shocks, suggesting that the dominant cause is something else.

That something else is the ultraviolet emission from young stars. These stars emit a lot more UV light than our Sun, and since it is a stable source of high energy, it can explain the continuous and extensive production of these simple molecules.

“Now, we have learned that starlight drives the formation of chemicals that are precursors to chemicals that we need to make life," said Patrick Morris, first author of the paper and researcher at Caltech in Pasadena, in the statement.