Researchers discover complex organic molecules in ring around planet

Using the Atacama Large Millimeter/submillimeter Array (ALMA), a group of researchers has for the first time identified a ring-shaped structure of complex organic molecules surrounding a newborn star – a discovery the report in the latest edition of The Astrophysical Journal.

While astronomers have long known that these molecules form in diffuse gas clouds which float in interstellar space, and believe that some of them were transported from this space between the stars into our solar system’s planet-forming disk about 4.6 billion years ago, the exact kinds and amounts of molecules originating from interstellar space remained a mystery.

However, those molecules, which include methanol (CH3OH) and methyl formate (HCOOCH3), played a vital role in the chemical evolution that ultimately resulted in the rise of life on Earth. In recent years, radio astronomy observatories have shown that such organic molecules exist around Solar-type protostars, but until now, those instruments were unable to resolve their distributions.

Now, researchers from the University of Tokyo and the RIKEN research institute used ALMA to analyze the distribution of different organic molecules around IRAS 16293-2422A, a Solar-type protostar located in the Rho Ophiuchi cloud complex, at a high-spatial resolution and discovered a that the object was surrounded by a ring of organic molecules 50 times the size of Earth’s orbit.

Findings show that how materials reach planetary systems differ

The size of the ring, they explained in a statement, is comparable to the size of the Solar System and the ring structure is believed to represent the boundary region separating infalling gas from a rotating disk-like structure around the protostar. During their observations, they clearly spotted a large concentration of both methyl formate and carbonyl sulfide (OCS).

They measured the motion of gas containing HCOOCH3 using the Doppler effect, and found “a clear rotation motion specific to the ring structure,” said Yoko Oya, a graduate student in physics at the University of Tokyo. The distribution of methyl formate around the protostar seems to be limited to a more confined region than the OCS distribution, which is primarily used to trace the infalling gases and which Oya’s team used to identify the HCOOCH3 and methanol.

According to the study authors, these saturated organic molecules originate in interstellar space and are preserved on the surfaces of dust grains. Once they reach the outer boundary of the disk, the shock created by collisions between the disk and infalling matter, combined with heating by the protostar’s light, causes the molecules to evaporate.

The new study provides the first direct evidence that organic materials from interstellar space do actually contribute to the formation of a planetary system by entering the rotating disk structures from which those systems originate. Combined with earlier research by the same team, in which they discovered a similar ring of sulfur monoxide around another Solar-type protostar, the paper demonstrates that the method through which materials are delivered to a planetary system differ from star to star, and could alter our understanding of how life originated here on Earth.

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Image credit: Caltech

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