“Building Blocks of Life Hidden in the Ice” – Largest Organic Molecule Detected in a Planetary Disc 


The formation of life from raw chemicals was more favorable in the early phases of our Solar System

Just add water, heat, and stir? Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, researchers at Leiden Observatory in the Netherlands have for the first time detected the precursors of prebiotic molecules such as amino acids and sugars, which are some of the basic building blocks of life. 

The molecule, dimethyl ether with nine atoms, the largest molecule identified in such a disc to date, was detected in the planet-forming disc around the young star Oph-IRS 48. 

Detected in Our Solar System

“We have actually detected dimethyl ether in our Solar System, namely in the comet 67P, which has formed from the dusty material in the disk as well, possibly at the same time as when planets were forming,” Nashanty Brunken with the Leiden Observatory wrote in an email to The Daily Galaxy. “Observing these complex organic molecules in planet-forming disks is more difficult however because these disks are usually very cold. As a result, such molecules are locked up in the ices in these disks and remain undetectable in the gas phase. The IRS48 is a warmer disk however and this causes the molecules to sublimate from these ices and become detectable.”

The image at the top of the page is an ESO artist’s impression shows the dust trap in the system Oph-IRS 48. The dust trap provides a safe haven for the tiny rocks in the disc, allowing them to clump together and grow to sizes that allow them to survive on their own. (ESO/L. Calçada)

Young Star Lights Up Disk of Life’s Building Blocks

The Bigger Picture –An Anthropic 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. It is very exciting to see how these findings fit into the bigger picture,” says Brunken, lead author of the study published today in Astronomy & Astrophysics.

By studying their formation and evolution, researchers can gain a better understanding of how prebiotic molecules end up on planets, including our own. “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. Hopefully with more observations we can get a step closer to understanding the origin of prebiotic molecules in our own Solar System,” says Nienke van der Marel, a Leiden Observatory researcher who also participated in the study.

Jumpstarting Abiogensis

The famous Miller-Urey experiment in 1952 simulated the expected conditions of early Earth – water, methane, ammonia, and hydrogen. By adding a source of energy – electric sparks to simulate lightning – Miller & Urey discovered that the basic molecules combined into complex amino acids. Today, astronomers are now discovering similar chemical reactions occurring in space, whereby ices, dust grains, and UV radiation interact to yield amino acids in planet-forming disks. Perhaps these early reactions in the disk can jumpstart abiogensis (the chemical process by which simplest life emerged from inanimate beginnings), and that the formation of life from raw chemicals was more favorable in the early phases of our Solar System than previously recognized. 



Never Before Found in a Planet-Forming Disc

Dimethyl ether is an organic molecule commonly seen in star-forming clouds, but had never before been found in a planet-forming disc. The researchers also made a tentative detection of methyl formate, a complex molecule similar to dimethyl ether that is also a building block for even larger organic molecules.

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

“Most disks are very cold, and molecules like dimethyl ether are hidden in ices on dust grains in the disk meaning we cannot observe them with telescopes like the Atacama Large Millimeter Array (ALMA), Booth told The Daily Galaxy. “IRS48 is a hotter star than the young sun would have been at a few million years old and the dust in the system has evolved in such a way that the ices are just the right distance from the star to sublimate and, this is far enough away from the star that we can resolve this region of the disk with ALMA.”

The molecules are located 444 light-years away in the constellation Ophiuchus –the subject of numerous studies because its disc contains an asymmetric “dust trap” –a cashew-nut-shaped region in its southern part, which traps millimeter-sized dust grains that can come together and grow into kilometer-sized objects like comets, asteroids and potentially even planets.

This region, which likely formed as a result of a newly born planet or small companion star located between the star and the dust trap, retains large numbers of millimeter-sized dust grains that can come together and grow into kilometer-sized objects like comets, asteroids and potentially even planets.

Many complex organic molecules, such as dimethyl ether, are thought to arise in star-forming clouds, even before the stars themselves are born. In these cold environments, atoms and simple molecules like carbon monoxide stick to dust grains, forming an ice layer and undergoing chemical reactions, which result in more complex molecules. Researchers recently discovered that the dust trap in the IRS 48 disc is also an ice reservoir, harboring dust grains covered with this ice rich in complex molecules. It was in this region of the disc that ALMA has now spotted signs of the dimethyl ether molecule: as heating from IRS 48 sublimates the ice into gas, the trapped molecules inherited from the cold clouds are freed and become detectable.


ESO Molecules

These images from the Atacama Large Millimeter/submillimeter Array (ALMA) show where various gas molecules were found in the disc around the IRS 48 star, also known as Oph-IRS 48. Recent observations spotted several complex organic molecules in this region, including formaldehyde (H2CO; orange), methanol (CH3OH; green) and dimethyl ether (CH3OCH3; blue), the last being the largest molecule found in a planet-forming disc to date. The emission signaling the presence of these molecules is clearly stronger in the disc’s dust trap, while carbon monoxide gas (CO; purple) is present in the entire gas disc. The location of the central star is marked with a star in all four images. The dust trap is about the same size as the area taken up by the methanol emission, shown on the bottom left. ALMA (ESO/NAOJ/NRAO)/A. Pohl, van der Marel et al., Brunken et al.

“What makes this even more exciting is that we now know these larger complex molecule 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.”

Fast Facts About Young Stars of the Milky Way

The discovery of dimethyl ether suggests that many other complex molecules that are commonly detected in star-forming regions may also be lurking on icy structures in planet-forming discs. 

“We were truly excited when we realized that we found dimethyl ether because that meant that these molecules are present in these regions where planets could be forming,” Brunken wrote in her email. “We can expect to find more complex organic molecules in other planet-forming disks which is very exciting for future studies of planet formation.”

Future studies of IRS 48 with ESO’s Extremely Large Telescope (ELT), currently under construction in Chile and set to start operations later this decade, will allow the team to study the chemistry of the very inner regions of the disc, where planets like Earth may be forming.

Source: “A major asymmetric ice trap in a planet-forming disk: III. First detection of dimethyl ether” (doi: 10.1051/0004-6361/202142981) to appear in Astronomy and Astrophysics.

Maxwell Moe, astrophysicist, NASA Einstein Fellow, University of Arizona via ESO

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