It is the largest molecule discovered to date in a planet-forming disk and a precursor to even larger organic molecules that in turn are building blocks for life.

Researchers write that in the magazine today Astronomy & Astrophysics† Their study deals with dimethyl ether: a large molecule found in the planet-forming disk around the young star IRS 48. The researchers studied this disk using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

Nine atoms

At nine atoms, dimethyl ether is the largest molecule found to date in a planet-forming disk. “It’s really exciting to finally detect these larger molecules in disks,” said researcher Alice Booth. “For a while we thought it might not be possible to observe them.”

star-forming regions

Dimethyl ether has previously been found in star-forming regions. Researchers suspect that the molecule – just like other (complex) molecules – see the light of day there even before the birth of stars. Because in these cold environments, atoms and simple molecules (such as carbon monoxide) easily adhere to dust grains, on which they form an ice layer and undergo chemical reactions, transforming them into new, more complex molecules.

And now the rather complex molecule dimethyl ether has also been found in a planet-forming disk around a young star, in other words the next phase in the evolution of star systems. “Now we know that these larger complex molecules are available to feed planets-to-be in the disk,” Booth said. “This was unknown until now, because these molecules are usually hidden in the ice.”

dust trap

Dimethyl ether has been found in a rather distinctive part of the planet-forming dust disk around IRS 48, namely in the dust trap. This region contains large numbers of millimeter-sized dust grains that can clump together to form much larger objects such as comets, asteroids and perhaps even planets. This dust trap is believed to have been created by a newborn planet or small stellar companion hiding somewhere between the parent star and the dust trap. Researchers recently discovered that this dust trap also serves as an ice reservoir: the dust grains are covered with ice rich in complex molecules. And dimethyl ether appears to be one of them. Trapped in the ice, the molecule is undetectable. But the heat from IRS 48 sublimates the ice and releases the trapped molecules – which originated in cold, star-bearing gas clouds – for ALMA to detect. “We are incredibly excited to now be able to track the entire journey of these complex molecules, from the clouds in which stars form, to planet-forming disks and comets,” said researcher Nienke van der Marel.

Life

The discovery of dimethyl ether strongly suggests that even more complex molecules – those we already know from star-forming regions – are waiting to be discovered in planet-forming disks. Researchers hope to find those molecules, because in this way more insight can be gained into the origin of life – here on Earth and possibly elsewhere. Because complex molecules such as dimethyl ether are the precursors of so-called prebiotic molecules – such as sugars and amino acids – or the building blocks of life. “Hopefully with more observations we can get one step closer to understanding the origin of prebiotic molecules in our own solar system,” said Van der Marel.

IRS 48 – and especially the dust disc around it – will undoubtedly receive more attention in the coming years. For example, researchers would like to study these in more detail with the Extremely Large Telescope† With this telescope it should also be possible to study the inner regions of the disk, where Earth-like planets could form.