Astronomers have often detected organic molecules in cosmic gas clouds and star-forming regions. Now they have also discovered the organic compound dimethyl ether in a planet-forming disk for the first time. It is the largest organic molecule in such a precursor of a planetary system to date. The evidence provides further evidence that important building blocks of life may have originated in space and in the rotating cloud of dust and gas around the young sun.
In order for life to develop, certain organic molecules are necessary, which form the building blocks of important proteins, cell wall components or genetic material. According to the theory, the forerunners of these building blocks of life could have originated in space. In fact, scientists have already detected some more complex organic molecules on comets, in cosmic dust clouds, and most notably in the cold molecular clouds of star-forming regions. In these cold environments, atoms and simple molecules like carbon monoxide stick to dust grains, forming a sheet of ice and undergoing chemical reactions that result in more complex compounds. “The formation and evolution of such molecules can help us to better understand how life originated in our own solar system,” explain Nashanty Brunken of Leiden University Observatory and her colleagues.
Molecule search in a protoplanetary disk
However, most of these more complex organic molecules have so far been discovered in stellar cradles, but whether and in what form they also occur in the protoplanetary disks around young stars has only been partially clarified. “However, studying these molecules in the planet-forming disks is crucial to understand how the material is integrated into the planets and what level of complexity is present in the different epochs of planet formation,” write Brunken and her team. However, especially in the case of more developed disks that have already cooled down more rapidly, many of these organic compounds are trapped in the ice layer around dust grains and can therefore hardly be detected via their spectral signatures.
However, this is different for the planet-forming disk around the young star IRS 48, which is about 444 light-years away from us in the constellation Ophiuchus. Previous observations have already revealed that this star is surrounded by a very asymmetric dust disk, with most of the dust concentrated in a cashew-shaped cloud. This shape is believed to have formed because the dust was being pushed there by the influence of a protoplanet or a smaller companion star. More important for the current study, however, is the fact that the young star is releasing intense UV radiation that has warmed the surrounding disk of dust and gas. If, as a result, parts of the ice layers on the dust grains sublimate into gas, their contents can be detected using spectral measurements. In this way, astronomers have already detected sulfur dioxide, sulfur monoxide and ethanol in the IRS-48 system.
dimethyl ether and methyl formate
In search of other, more complex organic molecules in this protoplanetary disk, Brunken and her team have now examined the young star and its dusty disk with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile – and have struck gold. They could find the signature of dimethyl ether (CH3OH3) demonstrate a compound of a total of nine atoms. “Dimethyl ether is the largest organic molecule ever discovered in a protoplanetary disk,” reports the team. In addition, the measurement data also indicate the presence of methyl formate (CH3OCHO) out. Both molecules have been previously discovered in stellar cradles but not in protoplanetary disks. They are regarded as possible precursors for important building blocks of life.
“It’s really fascinating to finally be able to track down these larger molecules in disks. For a while we thought it would not be possible to spot them,” says co-author Alice Booth from Leiden Observatory. “What makes it all even more exciting is the fact that we now know that these larger, complex molecules are present in the disk during the formation of planets.” to experience our own planet. “We hope that with further observations we will come a step closer to understanding the origin of the prebiotic molecules in our own solar system,” says Brunken’s colleague Nienke van der Marel. The team hopes to learn more about the chemistry in this and other protoplanetary disks in the future with the help of ESO’s under-construction Extremely Large Telescope (ELT).
Source: Nashanty Brunken (Leiden University) et al., Astronomy and Astrophysics, doi: 10.1051/0004-6361/202142981