Largest Organic Molecule Yet Found in Planet-forming Disk Could Aid Search for Alien Life

Astronomers have identified the largest organic molecule yet in a planet-forming disk of gas around a young star, a precursor to complex organic molecules that can lead to the emergence of life.

The molecule dimethyl ether spotted by the team in the planet-forming disk around the young star IRS 48, which is also called also known as Oph-IRS 48, is often found in stars forming clouds, but this marks its first detection in a planet-forming disk of gas and dust.

Leiden Observatory Assistant Professor Nienke van der Marel played a role in the discovery. She told Newsweek: "Dimethyl ether is the largest molecule ever detected in a planet-forming disk. It has been seen before in the cold clouds in which stars are forming, but not yet in an environment where planets are forming.

"This means that such molecules may end up on the planets directly as they form. The molecule is particularly important as it is a 'complex organic molecule', which is the starting point of large molecules that are the building blocks of life through further chemical reactions."

Leiden Observatory Masters student Nashanty Brunken told Newsweek: "These results give us a better understanding of the conditions that are required in order to form these
complex organic molecules and how they are eventually incorporated into
planetary material."

As these molecules are the precursors for larger organic molecules that serve as the building blocks for life, the research could help indicate which systems and planets are more likely to host life.

"Complex organic molecules are the precursor of pre-biotic molecules,
the building blocks of life. This means that from molecules such as dimethyl ether we can form larger and more complex molecules, such as amino acids and sugars, the ingredients for life," Brunken said.

Brunken, who is the lead author of a study detailing the finding in the journal Astronomy & Astrophysics, added in a press release: "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."

Brunken and the team detected the presence of the molecule in the disk located 444 light-years from Earth using the Atacama Large Millimeter/submillimeter Array (ALMA).

Leiden University astronomer and paper co-author, Alice Booth, told Newsweek: "The detection of these complex molecules in a warm disk-like IRS 48 where they cannot form in situ is very convincing evidence for interstellar inheritance.

"This means that the complex molecules in disks have an origin in the earlier cold dark cloud stage before stars have even formed. If you extrapolate this then it should mean that all exoplanet systems have the potential to host life."

A Cosmic Cashew

The young star IRS 48 has been a popular subject of study for astronomers thanks to the fact it hosts an asymmetric, cashew-nut-shaped "dust trap" region. The formation of this region was probably caused by the birth of a planet or a star between the main star and the dust trap.

In this dust trap, bigger dust grains can be trapped and could grow much larger by colliding and sticking together.

Study co-author van der Marel describes the region the team observed as a "comet factory" with the conditions needed for trapped particles to cluster and grow from millimeter-sized to comet-size. She added: "This discovery tells us that large complex molecules are present at the locations where planets are forming, as the dust trap is located on the edge of a gap that is possibly carved by a planet.

"The dust-trap itself is a high concentration of dust grains which may grow to a group of planetesimals, comets, or even a planet itself. Knowing that such molecules exist in the region of the disk where planets are forming tells us on which planets such molecules may end up and potentially develop life."

The researcher explained why the molecule hadn't been spotted before in such a disk and the vital role the ALMA telescope, located in the Atacama Desert region of northern Chile, played in the discovery. She said: "The ALMA telescope has much higher sensitivity than other telescopes observing at these wavelengths.

"Second, the dust trap in this particular disk is located close enough to the host star so that the ices are evaporating, whereas many disks have dust traps that are much colder as they are further out and/or the star is colder, so the ice remains frozen out onto the grains where it cannot be detected with ALMA."

She adds the highly asymmetric nature of the cashew-shaped dust trap around IRS 48 makes it easier to infer an emission originates from the dust grains, adding that for a ring-like dust trap this would be much harder to spot.

Booth highlighted the next steps for the astronomers: "IRS 48 may be one of only a few systems where these types of discoveries are possible. We plan to both obtain more sensitive data of IRS 48 to detect other more complex molecules, including those with nitrogen.

"We will also survey more nearby systems with ALMA to look for similar signatures in the disks around other young stars."

Oph-IRS 48
An artistic impression of the planet-forming disk around the IRS 48 star, also known as Oph-IRS 48. The disk contains a cashew-nut-shaped region in its southern part, which traps millimetre-sized dust grains that can come together and grow into kilometre-sized objects like comets, asteroids and potentially even planets. Astronomers have spotted the largest organic molecule in this region ever found in a planet forming disk. L. Calçada, ALMA ESO/NAOJ/NRAO/A. Pohl, van der Marel et al., Brunken et al./ESO