We have all been searching for clues of life through rovers on the surface of different planets, and through chemical footprints on ours. But have we been looking in the right place, or are we missing out on the not-so-obvious-looking corners of space? Scientists’ pursuit of the cosmic origin of life in the universe is taking them into interstellar space, not just planets. They have discovered a 13-atom organic molecule with sulfur— the largest ever identified in interstellar space. Sulfur, being a key ingredient for life, is churning out questions regarding why we might need to look closer into interstellar space in our hunt for the origin of our existence— from the basic biomolecules, to the complete man.
Sulfur is a critical component of amino acids, proteins, and enzymes. Sulfur atoms form disulfide bonds during protein folding, giving structure to the building blocks of the body. Sulfur is also a necessary fuel for ancient microbes, as an essential component of anaerobic respiration, which requires a strictly oxygen-free environment. It is also the 10th most abundant element in the universe. While sulfur-containing compounds similar to the newly discovered one have been found on comets and meteorites before, scientists fell behind in finding such large molecules in interstellar space— the vast region between stars scattered with clouds of gas and dust.
“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 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.”
Some researchers suggest that sulfur is rare in space because it is trapped within cosmic ice. The catalog comprises only 300 discovered compounds, but it is expanding. In fact, this discovery is special, given that the second-largest molecule is 9 atoms long, and even that is rare, since most others have 3 to 5 atoms. The new detection of larger molecules can fill the gap between simple chemistry found in space and the more complex biomolecules discovered on comets and meteorites.
The molecule, named 2,5-cyclohexadiene-1-thione, also contains carbon and hydrogen. It was found in a molecular cloud called G+0.693–0.027, approximately 27,000 light-years from Earth, near the center of the Milky Way. Molecular clouds are dense and cold concentrations of dust and gas that support the formation of molecules that eventually clump because of gravity, giving rise to baby stars, and so are aptly regarded as “stellar nurseries”.
Some of these clouds lead to the formation of planetary systems, such as the solar system, as the ingredients embedded in the molecular cloud are transferred to the planets. Researchers are trying to determine how, from simple molecules, we arrive at life as we see it on Earth. The picture has missing pixels, which the scientists are adding one by one.
The researchers prepared the compound from thiophenol— a malodorous compound containing carbon, hydrogen, and sulfur— using an electric discharge. Then the scientists obtained a radio fingerprint of the molecule and compared it with that from existing telescope data collected by the IRAM-30m and the Yebes radio telescopes in Spain.
The earlier observations have shown the abundance of sulfur molecules in this cloud, making it a good target for making new discoveries. One possible origin of life on Earth may have been collisions and impacts by small celestial objects, such as comets and meteorites, in the past, which created complex molecules that enabled life. Meteorites have large and complex sulfur compounds that they delivered on impact. However, the question remains: how did the meteorites and the comets get the supply of these molecules in the first place? The answer is tilting toward the idea that they could have come from regions outside the solar system, from molecule-rich areas of our galaxy, for now.
The discovery of such complex molecules near the center of the Milky Way suggests that Legos of life might be present everywhere, and could be key to the formation of life elsewhere, making the presence of life on another planet more likely.
Half a century ago, we thought that the harsh environment of space would break down compounds like this. The theory has been disproved by newer telescopes, which show that the chemistry of space is far richer than previously thought. Now, we are not limited to replicating conditions that gave rise to life on Earth, like the primordial soup, but are also taking notes on where the supply of the basic ingredients to prepare the soup came from.
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