Astronomers discover biggest molecule yet in a planet-forming disc

By utilising the Atacama Large Millimeter/submillimeter Array, scientists at Leiden Observatory have detected dimethyl ether in a planet-forming disc.

Researchers at the Leiden Observatory in the Netherlands have used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe dimethyl ether in a planet-forming disc for the first time. With a total of nine atoms, this is the biggest molecule detected in such a disc to date. It is also a precursor of larger organic molecules that can lead to the emergence of life.

“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,” explained Nashanty Brunken, a Masters student at Leiden Observatory, part of Leiden University, and lead author of the study published today in Astronomy & Astrophysics.

Dimethyl ether is an organic molecule frequently present in star-forming clouds, but it has never been found in a planet-forming disc before now.

“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,” added co-author Alice Booth, also a researcher at Leiden Observatory.

Planet-forming disc

The molecules were discovered in the planet-forming disc around the young star IRS 48 with the assistance of ALMA, an observatory co-owned by the European Southern Observatory (ESO). IRS 48, situated 444 light-years away from Earth in the constellation Ophiuchus, has been the centre of copious studies due to its disc comprising an asymmetric ‘dust trap’.

This region – which probably formed due to a new planet or small companion star situated between the star and the dust trap – maintains huge amounts of millimetre-sized dust grains that can come together and develop into kilometre-sized objects such as comets, asteroids and possibly even planets.

Scientists believe that numerous complex organic molecules, including dimethyl ether, occur in star-forming clouds before the stars are born. In these cold environments, atoms, and simple molecules such as carbon monoxide stick to dust grains, establishing an ice layer and experiencing chemical reactions, which result in more complex molecules.

An abundance of complex molecules

Researchers have now found that the dust trap in the IRS 48 disc also act as an ice reservoir, concealing dust grains covered with this ice rich in complex molecules. It was in this region of the disc that ALMA has now observed indications of the dimethyl ether molecule: such as heating from IRS 48 sublimates the ice into gas, the trapped molecules inherited from the cold clouds are liberated and become visible.

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

The discovery of dimethyl ether indicates that other complex molecules that are regularly identified in star-forming regions could also be present on icy structures in planet-forming discs. These molecules are the precursors of prebiotic molecules such as amino acids and sugars, which are some of the basic building blocks of life.

Understanding prebiotic molecules

By exploring their development and evolution, scientists can attain a greater comprehension 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,” concluded Nienke van der Marel, a Leiden Observatory researcher who also participated in the study.

Further studies of IRS 48 with ESO’s Extremely Large Telescope (ELT) – presently under construction in Chile and set to start operations later this decade, will enable the researchers to examine the chemistry of the very inner regions of the disc, where planets similar to Earth may be forming.

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