Artist’s concept of a protoplanetary disk around a star (left) and the “soup” of organic molecules in the disk (right). Image via M.Weiss/ CfA.

A series of new images taken with the ALMA telescope reveals that planets form in organic soups, each containing a unique mix of molecules.

Thanks to images taken with the ALMA (Atacama Large Millimeter / submillimeter Array) telescope, an international team of scientists is mapping the chemicals found in five protoplanetary disks, those regions of dust and gas where planets and they are located around young stars.

The project, called “Molecules with SOUL at planet formation scales,” has resulted in a series of twenty articles that will be published in a special issue of the Astrophysical Journal Supplement.

The new maps reveal that the chemicals in protoplanetary discs are not uniformly located on each disc; Instead, each is a planet-forming soup with a different mix of molecules. The results suggest that planet formation occurs in a variety of chemical environments and that, as they form, each planet can be exposed to very different molecules depending on their location on a disk. What is surprising is that in four of the five disks observed, deposits of complex organic molecules capable of creating biologically significant molecules were found. The presence of the molecules is significant because they are “stepping stones” between simpler carbon-based molecules, such as carbon monoxide, which is found in abundance in space, and more complex molecules that are required to create and sustain life.

“These planet-forming disks are packed with organic molecules, some of which are implicated in the origins of life here on Earth,” explains Karin Öberg, astronomer at the Center for Astrophysics | Harvard & Smithsonian (CfA), which led the mapping project. “The chemical compounds in each disk will ultimately affect the type of planets that form and determine whether the planets can support life or not.”

The research team was looking for three molecules: cyanoacetylene (HC3N), acetonitrile (CH3CN) and cyclopropenylidene (c-C3H2), in five protoplanetary disks, known as IM Lup, GM Aur, AS 209, HD 163296 and MWC 480. The Los Protoplanetary disks range between 300 and 500 light years from Earth. All discs show signatures of ongoing planetary formation.

Protoplanetary Disks “Feed” Young Planets
The protoplanetary disk surrounding a young planet will “feed” it material as it forms. For example, it is believed that the young Earth was seeded with material through the impacts of asteroids and comets that had formed in the protoplanetary disk around the Sun.

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

“If we find molecules like these in such large quantities, our current knowledge of interstellar chemistry suggests that even more complex molecules should also be observable,” said John Ilee, a researcher at the University of Leeds who was also involved in the work.