Planets are born in cosmic organic soups

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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.

Planets are born in cosmic soups

Soup lovers know that there are many different kinds of soup, with a wide variety of tasty ingredients to make them unique. On September 15, 2021, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, published new evidence related to “cosmic soups” around stars, from which distant exoplanets form. These cosmic soups are the mixture of chemicals in the protoplanetary discs around young stars. These disks are the cradles of the planets. Astronomers have now mapped out the ingredients – the chemicals in five different protoplanetary disks – in extraordinary detail. They discovered that, just like with culinary specialties on Earth, no two cosmic soups are the same.

CfA astronomer Karin Öberg led the mapping project.

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No less than 20 new peer-reviewed papers, collectively named “Molecules with ALMA at Planet-forming Scales (MAPS)”, have been accepted for (pending) publication in the Supplement to the Journal of Astrophysics. They are also currently available in pre-printed versions on arXiv (the first 20 articles listed).

Light spot inside a larger dimming ring with a black circle in the center and a black background.
This photo from ESO’s Very Large Telescope shows a new baby planet (bright spot inside space) around the star PDS 70. Planets like this form inside soups of organic molecules around their stars. Image via ESO / A. Müller et al / AASnova.

Implications for life

Specifically, astronomers looked at five different protoplanetary disks and found dozens of different organic molecules. Protoplanetary disks are massive, disk-shaped clouds of gas and dust around young stars. In fact, it is in these discs that the planets are formed. These soups of organic molecules are all different from each other and, therefore, may have implications for the possibility of life.

As Öberg said in a statement:

These discs forming planets are teeming with organic molecules, some of which are involved in the origins of life here on Earth. It’s really exciting; the chemicals in each disc will ultimately affect the type of planets that form and determine whether or not the planets can harbor life.

Each soup is unique

Organic chemicals, however, are not distributed evenly across the discs. Instead, their locations are more random, meaning each soup is unique with its own mix of ingredients. This suggests that planets can form in a wide variety of chemical environments. The location of a planet in the disk also makes a big difference, as berg explained:

Our maps show that where a planet forms on a disk is very important. Many chemicals in discs are organic, and the distribution of these organics varies considerably within a particular disc. Two planets can form around the same star and have very different organic inventories, and therefore predispositions to life.

Smiling woman with long red hair.
The new mapping project was led by Karin Öberg from CfA. Image via the Center for Astrophysics | Harvard and Smithsonian.

Our team used these maps to show where some of the forming planets are located in the disks, allowing scientists to relate the observed chemical soups to future compositions of specific planets.

Location, location, location

In total, the researchers mapped 18 different organic molecules in protoplanetary disks. This includes hydrogen cyanide and other nitriles linked to the origins of life. The Maps III study which identified the specific locations of molecules was led by CfA graduate student Charles Law. Law and his colleagues used the Atacama Large Millimeter / submillimeter Array (ALMA) in 2018 and 2019 to study the five protoplanetary disks.

Indeed, they were able to collect so much data that it took two years to analyze the results. A 100 terabyte hard drive was also needed to store the data. The data was not only plentiful, it also had surprises in store, with Law noting that:

Understanding the chemistry that occurs even in a single disc is much more complicated than we might think. Each individual disc appears quite different from the next, with its own distinctive set of chemical substructures. The planets that form in these disks will experience very different chemical environments.

White spot in the center of the disc in concentric shades of lighter to darker blue on a black background.
This composite image of ALMA data from the young star HD 163296 shows an emission of hydrogen cyanide posed on a star field. Hydrogen cyanide is one of 18 organic molecules identified by the MAPS mapping project. Image via ALMA (ESO / NAOJ / NRAO) / D. Berry (NRAO) / K. Öberg et al (MAPS) / Center for Astrophysics | Harvard and Smithsonian.

In search of newborn planets

Richard Teague, member of the Submillimeter Array group at CfA, used the data and images collected by MAPS to search for newborn planets in protoplanetary disks. They are difficult to see directly, due to the obscuring of gas and dust. He said:

It’s like trying to see a fish underwater. We know they’re there, but we can’t look that far. We need to look for subtle signs on the surface of the water, like ripples and waves.

Despite this, the researchers were lucky. Teague analyzed the gas velocities in two of the five protoplanetary disks. These disks were around young stars HD 163296 and MWC 480. As a result, they found small hiccups of speed in parts of the disks, revealing a young Jupiter-like planet embedded in each of the disks.

As the planets grow larger, they will gradually dig holes in the disks, like other holes that already exist and can be seen by telescopes. The upcoming James Webb Space Telescope should be able to spot the planets themselves, as Teague noted:

He should have the sensitivity to locate the planets.

It will be interesting to see how many newborn planets Webb finds and what ingredients are present in their individual soups.

Conclusion: the astronomers of the Center for Astrophysics | Harvard & Smithsonian (CfA) discovered that planets are born in cosmic soups of organic molecules. These soups have different ingredients, leading to a great diversity of planets.

Source (preprint): Molecules with ALMA at scales forming planets

Via the Harvard-Smithsonian Center for Astrophysics

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