The largest molecule ever found in a proto-planet disc could be a precursor to life - Inverse

In the surroundings of a young star located 444 light years away, a team of astronomers found what may be the precursor to life itself.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, researchers from the Netherlands have detected the largest molecule ever found in a planet-forming disc around a star. The molecule could be a precursor to large organic molecules, potentially leading to the formation of some form of life.

The researchers detailed their findings in a study published Tuesday in Astronomy and Astrophysics.

“It is really exciting to finally detect these larger molecules in discs,” Alice Booth, a researcher at Leiden Observatory in the Netherlands and co-author of the study, said in a statement. “For a while we thought it might not be possible to observe them.”

WHAT’S NEW — For years, astronomers have been observing a star dubbed IRS 48 located around 400 light years away from Earth in the constellation Ophiuchus. But it’s not for the star itself — rather, it’s to observe the protoplanetary disc surrounding the star.

The protoplanetary disc surrounding the young star IRS 48 has a cashew-shaped dust trap in its southern region, which traps tiny grains of dust.ESO/L. Calçada, ALMA (ESO/NAOJ/NRAO)/A. Pohl, van der Marel et al., Brunken et al.

Protoplanetary discs are clouds of gas particles and swirls of dust that form in unison with the birth of a star. The gas and dust collide with one another as they orbit around the star, eventually growing into a larger body— a planet.

The planet-forming disc around IRS 48 is already quite peculiar. Previous observations showed that the dust particles are gathered in a crescent shape while the gas and smaller dust grains form a ring-shaped disc.

The proplanetary disc’s so-called “dust trap” is asymmetrical and shaped like a cashew nut. It contains a lot of millimeter-sized dust grains that fuse to grow into larger objects like comets, asteroids, and potentially even planets.

The image shows the different complex organic molecules spotted in the planet forming disc around IRS 48, including formaldehyde (orange), methanol (green) and dimethyl ether (blue).ALMA (ESO/NAOJ/NRAO)/A. Pohl, van der Marel et al., Brunken et al.

During more recent observations using ALMA, the team of researchers behind the study discovered dimethyl ether in the protoplanetary disc.

HERE’S THE BACKGROUND — Dimethyl ether is an organic molecule formed from nine atoms, making it the largest molecule ever detected in a planet-forming disc. It is the precursor of prebiotic molecules such as amino acids and sugars.

The molecule is commonly found in star-forming clouds, but astronomers had never discovered it in a planet-forming disc. Organic molecules are considered the building blocks of life on Earth — which could carry over to elsewhere in the universe.

“From these results, we can learn more about the origin of life on our planet and therefore get a better idea of the potential for life in other planetary systems,” Nashanty Brunken, a graduate student at Leiden Observatory, and lead author of the study, said in a statement. “It is very exciting to see how these findings fit into the bigger picture.”

The green region shows where the larger particles are located while the orange ring shows observations of much finer dust particles.ALMA (ESO/NAOJ/NRAO)/Nienke van der Marel

Scientists believe that complex organic molecules such as dimethyl ether form in star-forming clouds, before the stars themselves are born. These regions are extremely cold, with temperatures between 10 to 20 Kelvin, which allows for a layer of ice to form over atoms and simple molecules in order to form more complex molecules.

So how then was dimethyl ether discovered in a protoplanetary disc? Scientists observed that this particular disc’s dust trap is also an ice reservoir, containing dust grains covered with complex molecule-laden ice.

As the heat from IRS 48 turns the ice into gas, the molecules that were trapped in the ice from the cold clouds are thawed, allowing astronomers to glimpse their spectra.

“What makes this even more exciting is that we now know these larger complex molecules are available to feed forming planets in the disc,” explains Booth. “This was not known before as in most systems these molecules are hidden in the ice.”

The recent discovery could mean that this type of organic molecule can be found in planet-forming discs, perhaps just hiding beneath a layer of ice.

WHAT’S NEXT — The team behind the study is hoping to use the Extremely Large Telescope, which is currently under construction, to do follow-up observations of IRS 48.

The telescope will allow them to look deeper into the chemical makeup of the inner regions of the protoplanetary disc in order to better understand how planets like Earth form.

“We are incredibly pleased that we can now start to follow the entire journey of these complex molecules from the clouds that form stars, to planet-forming discs, and to comets,” Nienke van der Marel, a Leiden Observatory researcher, and co-author of the study, said in a statement. “Hopefully with more observations we can get a step closer to understanding the origin of prebiotic molecules in our own Solar System.”

Abstract: The complex organic molecules (COMs) detected in star-forming regions are the precursors of the prebiotic molecules that can lead to the emergence of life. By studying COMs in more evolved protoplanetary disks we can gain a better understanding of how they are incorporated into planets. This paper presents ALMA band 7 observations of the dust and ice trap in the protoplanetary disk around Oph IRS 48. We report the first detection of dimethyl ether (CH₃OCH₃) in a planet-forming disk and a tentative detection of methyl formate (CH₃OCHO). We determined column densities for the detected molecules and upper limits on non-detected species using the CASSIS spectral analysis tool. The inferred column densities of CH₃OCH₃ and CH₃OCHO with respect to methanol (CH₃OH) are of order unity, indicating unusually high abundances of these species compared to other environments. Alternatively, the ¹²CH₃OH emission is optically thick and beam diluted, implying a higher CH₃OH column density and a smaller emitting area than originally thought. The presence of these complex molecules can be explained by thermal ice sublimation, where the dust cavity edge is heated by irradiation and the full volatile ice content is observable in the gas phase. This work confirms the presence of oxygen-bearing molecules more complex than CH₃OH in protoplanetary disks for the first time. It also shows that it is indeed possible to trace the full interstellar journey of COMs across the different evolutionary stages of star, disk, and planet formation.