Astrophysicists identify ‘large reservoirs’ of organic molecules needed to form the basis of life

Artist’s impression of gas and dust in the protoplanetary disk surrounding the young star. The inset shows the molecular gas targeted by the MAPS observations, made up of a “soup” of simple and complex molecules near planets still forming. Credit: M.Weiss / Center for Astrophysics / Harvard & Smithsonian

Analysis of single fingerprints in the light emitted from matter surrounding young stars has revealed “significant reservoirs” of large organic molecules needed to form the basis of life, the researchers said.

Dr John Ilee, a University of Leeds researcher who led the study, said the findings suggest that the basic chemical conditions that resulted in life on Earth may exist more widely across the Galaxy.

Large organic molecules have been identified in protoplanetary disks surrounding newly formed stars. A similar disc would once have surrounded the young Sun, forming the planets that now make up our solar system. The presence of the molecules is important because they are “stepping stones” between simpler carbon-based molecules such as carbon monoxide, which are found in abundance in space, and more complex molecules which are needed for create and maintain life.

Details of the study are released today (September 15, 2021) and will appear in the Astrophysical Journal Supplements Series. This is one of 20 papers reporting on a major international investigation into the chemistry of planet formation.

Dr. Catherine Walsh of the School of Physics and Astronomy was one of five Co-PIs leading the investigation. Called the ‘molecules with ALMA in the Planet-forming Scales (or MAPS) program, he used data collected by the Atacama Large Millimeter / submillimeter Array (or ALMA) radio telescope in Chile.

Dr Ilee and his team, made up of astrophysicists from 16 universities around the world, focused on studying the existence, location and abundance of precursor molecules necessary for the formation of life. .

He said: “These large, complex organic molecules are found in various environments across space. Theoretical and laboratory studies have suggested that these molecules are the “raw ingredients” to build molecules that are essential components of biological chemistry on Earth, creating sugars, amino acids, and even the ribonucleic components acid (RNA) under the right conditions.

“However, many of the environments in which we find these complex organic molecules are quite distant from where and when we think planets form. We wanted to know more about where exactly and to what extent these molecules were present in them. the birthplaces of the planets – the protoplanetary disks. ”

ALMA – observe chemistry deep in space

The investigation was made possible by advances in the ability of the ALMA telescope to detect very weak signals from molecules in colder regions of space.

At ALMA, a network of more than 60 antennas is assembled so that the observatory can detect the signal from these molecules. Each molecule emits light at distinct wavelengths producing a unique spectral “fingerprint”. These fingerprints allow scientists to identify the presence of molecules and study their properties.

Dr Walsh explained, “The power of ALMA has enabled us for the first time to measure the distribution and composition of matter that actively builds planets around nearby young stars. The telescope is powerful enough to do this even for large, complex molecules that are the precursors of life. “

The research team looked for three molecules – cyanoacetylene (HC3N), acetonitrile (CH3CN) and cyclopropenylidene (vs-C3H2) – in five protoplanetary disks, known as IM Lup, GM Aur, AS 209, HD 163296 and MWC 480. Protoplanetary disks are located between 300 and 500 light years from Earth. All of the disks show signatures of the continuing formation of planets occurring within them.

Protoplanetary disks “feed” young planets

The protoplanetary disc that surrounds a young planet will “feed” it with matter as it forms.

For example, it is believed that young Earth was seeded with matter via impacts from asteroids and comets that had formed in the protoplanetary disc around the Sun. But scientists were unsure whether all protoplanetary disks contained reservoirs of complex organic molecules capable of creating biologically significant molecules.

This study begins to answer that question. He found the molecules in four of the five discs observed. In addition, the abundance of molecules was greater than what scientists had expected.

Dr Ilee said, “ALMA has allowed us for the first time to search for these molecules in the innermost regions of these disks, at similar size scales to our solar system. Our analysis shows that the molecules are mainly located in these internal regions with abundances between 10 and 100 times greater than what the models had predicted. “

It is important to note that the regions of the disc in which the molecules were located are also where asteroids and comets form. Dr Ilee says it’s possible that a process similar to the one that may have helped initiate life on Earth could also occur in these disks – where bombardment by asteroids and comets transfers large organic molecules to planets. newly formed.

Dr Walsh added: “The key result of this work shows that the same ingredients needed to seed life on our planet are also found around other stars. It is possible that the molecules needed to start life on the planets are readily available in all planet-forming environments. “

One of the next questions the researchers want to investigate is whether even more complex molecules exist in protoplanetary disks.

Dr Ilee added, “If we find molecules like these in such great abundance, our current understanding of interstellar chemistry suggests that even more complex molecules should be observable as well. “

“We hope to use ALMA to research the next springboards of chemical complexity in these discs. If we detect them, we will be even closer to understanding how the raw ingredients of life can be assembled around other stars. “

Reference: “Molecules with ALMA at Planet-forming Scales (MAPS) IX: Distribution and properties of the large organic molecules HC3N, CH3CN, and c-C3H2” September 15, 2021, The Astrophysical Journal Supplement Series.