Molecules Needed For Life Found In Abundance In Planet-Forming Disks

In this artist's impression, planets form from the gas and dust in the protoplanetary disk surrounding the young star and complex molecules emerge alongside the planets. Image Credit: M.Weiss/Center for Astrophysics | Harvard & Smithsonian

The formation of life is a topic still full of uncertainties but scientists believed that certain molecules are necessary to be present for things like RNA and DNA to arise. Such molecules have been spotted in space before, and now astronomers report that large reservoirs of them exist where planets form.

Astronomers studied five star systems known to have a young star surrounded by a protoplanetary disk where planets are actively forming. Four of them have the unique chemical fingerprints of these molecules — cyanoacetylene (HC3N), acetonitrile (CH3CN), and cyclopropenylidene (c-C3H2) — and they were more abundant than the team expected.

The observations, using the Atacama Large Millimetre/submillimetre Array (ALMA), are published in the Astrophysical Journal Supplement Series together with 19 other papers investigating the chemistry of protoplanetary disks.

“ALMA has allowed us to look for these molecules in the innermost regions of these disks, on size scales similar to our Solar System, for the first time," lead author Dr John Ilee, said in a statement. "Our analysis shows that the molecules are primarily located in these inner regions with abundances between 10 and 100 times higher than models had predicted."

The regions where these large reservoirs of organic molecules are found is where not just planets but also asteroids and comets form. Complex chemical structures are not just found in interstellar space but also around the stars themselves.

protoplanetary disks
The four rotoplanetary disks – GM Aur, AS 209, HD 163296 & MWC 480. The top row shows emissions from large (millimeter-sized) dust in the disks. The bottom row shows a three-color composite image of emissions from the large organic molecules HC3N (red), CH3CN (green), and c-C3H2 (blue). Dashed circles with a radius of 50 astronomical units indicate the scale of the comet-forming region in our own Solar System. Image Credit: Dr J.D.Ilee/University of Leeds

“These large complex organic molecules are found in various environments throughout space. Laboratory and theoretical studies have suggested that these molecules are the ‘raw ingredients’ for building molecules that are essential components in biological chemistry on Earth, creating sugars, amino acids, and even the components of ribonucleic acid (RNA) under the right conditions,” Dr Ilee explained.  

“However, many of the environments where we find these complex organic molecules are pretty far removed from where and when we think planets form. We wanted to understand more about where exactly, and how much of, these molecules were present in the birthplaces of planets – protoplanetary disks.”

The presence of these molecules in large quantities suggests that it might be possible to detect the chemical signatures of even more complex ones. The possible building blocks of life might actually be detectable with ALMA.

“If we are finding molecules like these in such large abundances, our current understanding of interstellar chemistry suggests that even more complex molecules should also be observable,” Dr Ilee added.

“We’re hoping to use ALMA to search for the next stepping stones of chemical complexity in these disks. If we detect them, then we’ll be even closer to understanding how the raw ingredients of life can be assembled around other stars.”

 

 
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