Scientists discover molecule in space that hints at origin of life

A 13-atom molecule containing sulfur (seen in this illustration) was discovered in interstellar space for the first time. MPE/NASA/JPL-Caltech via CNN Newsource

Scientists have discovered the largest organic molecule containing sulfur — a key ingredient for life — ever identified in interstellar space. The researchers call the discovery a “missing link” in scientists’ understanding of the cosmic origins of life’s chemistry.

Sulfur is the 10th most abundant element in the universe and a critical component of amino acids, proteins and enzymes on Earth. But while researchers had previously found sulfur-bearing molecules similar to the newly discovered one in comets and meteorites, there was a puzzling lack of large molecules including sulfur in interstellar space — the vast region between stars that is scattered with clouds of dust and gas.

“Sulfur came to Earth from space long, long ago,” said Mitsunori Araki, a scientist at the Max Planck Institute for Extraterrestrial Physics in Germany and lead author of a study on the discovery, which was published last week in the journal Nature Astronomy.

“However, we have only found a very limited amount of sulfur-bearing molecules in space, which is strange. It should exist in huge amounts, but it’s very difficult to find.”

A different team of researchers previously suggested that sulfur might appear to be rare in space because it’s trapped in cosmic ice — hiding in plain sight rather than missing.

The new detection, therefore, adds an important piece to this puzzle. “This is the largest sulfur-bearing molecule ever found in space, at 13 atoms,” Araki said. “Before this one, the largest only had nine atoms, but it was already a rare case, because most detected sulfur-bearing molecules only had three, four or five atoms.”

Finding larger molecules is important, he added, because it helps to fill an existing gap between simple chemistry found in space and the more complex building blocks of life that have been discovered in comets and meteorites.

The molecule, which also contains carbon and hydrogen, is called 2,5-cyclohexadiene-1-thione and adds to a growing catalog of over 300 molecules observed in space so far. The finding, Araki said, suggests that many more molecules containing sulfur, perhaps even larger, could be detected in the future.

Stellar nurseries

The molecule was found within a molecular cloud called G+0.693–0.027 about 27,000 light years from Earth, near the center of our galaxy.

Molecular clouds are cold and dense concentrations of dust and gas that allow for the formation of molecules. They act as stellar nurseries as gravity creates clumps that eventually become baby stars.

“A molecular cloud is where star formation is happening,” said Valerio Lattanzi, also a scientist at the Max Planck Institute for Extraterrestrial Physics and a coauthor of the study.

Eventually, Lattanzi added, some of these clouds will lead to the formation of planetary systems like our own solar system. “The ingredients that are embedded in the molecular cloud will be transferred to the planets,” he said.

“We are trying to find out what the ingredients that will eventually form life are, trying to understand how from simple molecules we get to life as we know it on Earth. And we are trying to add elements to this picture, one by one.”

Researchers first synthesized the molecule by applying an electric discharge to a substance called thiophenol — a foul-smelling liquid containing sulfur, carbon and hydrogen.

They then obtained an extremely precise “radio fingerprint” of the molecule that they compared with existing telescope data from the observation of the cloud, collected by the IRAM-30m and the Yebes radio telescopes in Spain.

“We had seen from earlier observation that sulfur molecules were quite abundant in this cloud,” Lattanzi said. “That’s why it was a very good target for us. We believe that one of the possible origins of life on Earth is through collisions and impacts of small body systems like comets and meteorites with our planet in the past, that probably brought complex molecules, including ones containing sulfur. So that’s what we are trying to do — to connect these missing links in the path to eventually form life as we know it.”

‘An exciting detective story’

Kate Freeman, Evan Pugh University Professor of Geosciences at Penn State University, called the study “an exciting detective story made possible by powerful radio telescopes and a really good search strategy.”

Meteorites are known to have large and complex sulfur compounds, said Freeman, who was not involved in the research, and they likely delivered many of them to Earth to help set the stage for the chemistry of life.

“Yet, we didn’t really know how these compounds ended up in meteorites or their precursor planetary bodies,” she added in an email. “Now we know there is at least a good possibility some of them could be derived from outside the solar system, from molecule-rich regions of our galaxy like the area studied by the authors.”

Sulfur is one of only six elements essential to life on Earth and may have been a critical ingredient in the earliest life on Earth, providing vital fuel to ancient microbes, according to Sara Russell, a professor of planetary sciences at the Natural History Museum in London.

“The presence of complex organic molecules in the centre of our Milky Way implies that biologically important materials may be everywhere in space,” Russell, who did not participate in the study, said in an email.

“Finding such molecules such a long way from our home planet also suggests that similar processes may be happening elsewhere — it makes the presence of life existing on another planet that little bit more likely.”

Ryan Fortenberry, an associate professor of chemistry and biochemistry at the University of Mississippi, said the findings excited him. “Sulfur as an atom exists in a very special place on the periodic table.

It has a unique chemistry that allows molecules to do much more than what only oxygen, nitrogen, and carbon would allow,” Fortenberry said via email. “Finding molecules with sulfur in them helps us to better gauge where life could’ve started, and where it could end up.”

More than 50 years ago it was a miracle to find any molecules in space, added Fortenberry, who was also not part of the study.

“The common thinking was that the harsh environment would simply break them down — now we’re finding molecules with 13 atoms and some with multiple dozen atoms,” he said.

“Molecules are more resilient than we gave them credit for, and telescopes have shown us that the chemistry of space is far richer than we could have imagined. I fully expect that we will find amino acids in space beyond our solar system.”