ALMA's surprise chemical find unveils hidden protoplanets

Astonishing chemical evidence discovered by ALMA scientists unveils the formation of protoplanets.
Abdul-Rahman Oladimeji Bello
Star cluster and plasma
Star cluster and plasma


Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) have made an extraordinary chemical discovery that could revolutionize our ability to detect and confirm the existence of protoplanets.

Protoplanets are the early stages of planet formation. They are essentially young, developing planets that are still accreting mass from a protoplanetary disk—a disk of gas and dust surrounding a young star.

This finding, recently published in The Astrophysical Journal Letters and reported by National Radio Astronomy, promises to provide astronomers with an alternative method for studying these elusive celestial bodies when direct observations or imaging are not feasible.

The star at the center of this captivating research is HD 169142, a young star located in the constellation Sagittarius. What makes HD 169142 particularly intriguing to astronomers is its impressive circumstellar disk, teeming with dust and gas, which happens to be viewed almost face-on.

Over the past decade, several potential protoplanet candidates have been identified in this system. Earlier this year, scientists from the University of Liège and Monash University confirmed that one of these candidates, HD 169142 b, is a colossal protoplanet akin to Jupiter.

Thanks to a fresh analysis of archival data from ALMA, an international collaboration that includes the National Radio Astronomy Observatory (NRAO), scientists have stumbled upon the most compelling chemical evidence yet of protoplanetary formation.

"When we looked at HD 169142 and its disk at submillimeter wavelengths, we identified several intriguing chemical signatures of this recently-confirmed gas giant protoplanet," exclaimed Charles Law, lead author of the study and an astronomer at the Center for Astrophysics | Harvard & Smithsonian. "This breakthrough confirms that chemical signatures can help us discern the types of planets that may be forming around young stars."

The research team honed in on the HD 169142 system, anticipating that detectable chemical signatures would accompany the presence of the giant protoplanet HD 169142 b. Their hunch proved correct. The team detected carbon monoxide (12CO and its isotopologue 13CO) and sulfur monoxide (SO), chemicals previously associated with protoplanets in other disks.

However, the real surprise came when they detected silicon monosulfide (SiS) for the first time. This discovery is astonishing because the emission of SiS by ALMA requires the release of silicates from nearby dust grains through powerful shock waves caused by the gas moving at high velocities—behavior typically linked to outflows driven by giant protoplanets.

"The detection of SiS emission caught us off guard since we had never observed this molecule before in a protoplanetary disk, let alone in proximity to a giant protoplanet," Law explained. "It implies that this protoplanet is generating intense shock waves in the surrounding gas."

The implication of the research.

With this groundbreaking chemical approach, scientists may now have a new avenue for detecting and characterizing young protoplanets, offering fresh insights into exoplanets and deepening our understanding of these distant worlds.

ALMA's surprise chemical find unveils hidden protoplanets

Protoplanets, especially those nestled within their parental circumstellar disks like those in the HD 169142 system, provide a direct link to the exoplanet population we know of. Law emphasized the significance of this discovery, stating, "Using chemical signatures observed with ALMA allows us to grasp the incredible diversity of exoplanets, understand how different protoplanets evolve, and ultimately connect their properties to those of exoplanetary systems.

This revelation not only presents a new tool for planet-hunting with ALMA but also unveils a world of exciting chemistry we've never encountered before. As we continue to survey more disks surrounding young stars, we can expect to stumble upon other unexpected and captivating molecules, just like SiS. These discoveries hint at the immense chemical diversity associated with protoplanetary environments, reminding us that we've barely scratched the surface.

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