Gazing into the remote reaches of space at a nascent star, astronomers have possibly unearthed a new perspective on the ancient origins of our solar system.

Employing a combination of data from the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA) based in Chile, a team of international researchers has captured a rare glimpse into the initial stages of planet formation surrounding the young star HOPS-315, situated in a massive star-forming nebula roughly 1,400 light-years away in the Orion constellation. Their discoveries were detailed in a recent issue of Nature.

With a mass about 0.6 times that of the sun, HOPS-315 is expected to evolve into a star similar to our sun, making it an ideal proxy for exploring the early phases of our solar system’s development. Currently, however, it is enveloped by a thick cloud of material funneling toward it, serving as nourishment for the growing star.

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Yet the powerful infrared capabilities of JWST and the radio waves from ALMA have penetrated this dense cloud, allowing a look through a gap in the envelope to scrutinize structures around HOPS-315 with exceptional clarity—most notably a spinning protoplanetary disk of hot gas and dust. These disks are the birthplaces of planets, where initially, small rock clusters known as planetesimals begin to form and gradually assemble into fully developed planets.

However, no planetesimals can emerge without first the formation of tiny crystalline mineral grains within the disk as it cools. This crucial step has largely remained a mystery to astronomers, obscured by the dense clouds surrounding young stars. Similarly, planetary scientists who study our solar system face a vast temporal divide of over 4.5 billion years since the formation of our sun and its planets.

The scant evidence we possess from this primordial period mainly exists in the form of calcium-aluminum-rich inclusions (CAIs) found within ancient meteorites. Radiometric dating has identified these CAIs as the oldest solid materials formed around the sun, indicating they may have been the initial seeds from which planets eventually sprouted. These CAIs set the chronological baseline for our solar system’s timeline, marking their formation as “time zero.”

The prevailing theory suggests that CAIs were produced from mineral grains that condensed from the cooling disk of gas encircling our newborn sun. But the specific details of how, where, and when this happened remain elusive. Without a way to travel back in time, the next best option is to study similar processes around other young stars like HOPS-315, which until now have been poorly observed.

“Previously, we’ve mostly seen older, colder protoplanetary disks,” explains Melissa McClure, the study’s lead author and an astronomer at Leiden University in the Netherlands. “The window for forming mineral grains and CAIs is incredibly brief, about 100,000 years. If you blink, you might miss it. And young protostars are often hidden within dense molecular clouds, making them difficult to observe.”

However, HOPS-315 is not only very young but also oriented in such a way relative to our solar system that allows astronomers to observe it more deeply and closely. “This system is unique,” comments Fred Ciesla, a planetary scientist at the University of Chicago, who reviewed the Nature paper and wrote an accompanying commentary. “It possesses a hot inner disk still in its formative phase and is angled in a way that we can actually see inside. This makes it quite special, and there’s likely much more to learn from it.”

A major factor in these new insights was the JWST; earlier observations by other instruments like NASA’s Spitzer Space Telescope identified the system as a promising target but lacked the capabilities for detailed follow-up. “The significant enhancements in sensitivity and spectral resolution provided by Webb made this possible,” McClure notes.

With the cosmic alignment in their favor, McClure and her colleagues conducted observations of HOPS-315 with JWST in March and September of 2023. A meticulous analysis of the data revealed molecular signatures of gaseous silicon monoxide and a variety of crystalline silicates—clear indicators of solid mineral grains forming as the hot gas in the protoplanetary disk cools. While HOPS-315 is also emitting a jet of material as it feeds, further observations with ALMA in November 2023 confirmed that the mineral grains were not in the jet, but rather in a part of the protostar’s disk twice the distance from Earth to the sun—a region analogous to the main asteroid belt in our solar system. The dynamics of the disk or intense stellar winds from the developing protostar might be aiding the aggregation of these grains.

Although the JWST and ALMA data did not directly reveal CAIs, the ratios and locations of the detected minerals around HOPS-315 align with many models predicting the conditions conducive to CAI formation at “time zero” in the early solar system.

“This new research strongly suggests that, for HOPS-315, conditions favorable for CAI formation are present within about one Earth-sun distance at an early stage—a few hundred thousand years after the protostar’s formation,” states Phil Armitage, a planet formation theorist at Stony Brook University and the Flatiron Institute in New York City, who was not involved in the study. While not entirely unexpected, he remarks, “it’s conceivable that CAIs could form significantly earlier or later in a protostar’s lifecycle.”

Ilaria Pascucci, an astronomer at the University of Arizona and also not a part of the new study, underscores that the findings are so fundamentally significant that they warrant thorough investigation and follow-up. “Detecting CAIs in protoplanetary disks would be crucial, as it would bridge the development of these disks with that of the solar system,” she explains. “However, the authors have not yet detected CAIs; they’ve found crystalline grains that could have formed in an environment conducive to CAI formation. It’s a compelling connection.”

Studying protostars like HOPS-315 can be highly challenging due to their complexity, including the presence of the star, disk, wind, jet, and envelope. “The authors have skillfully extracted all the available information from their observations of HOPS-315, but given the complexities, it’s essential to continue exploring more systems,” Pascucci adds. One such protostar, HOPS-68, observed by Spitzer in 2011, exhibited similar traits in the data available then, which were interpreted as part of the protostar’s obscuring envelope rather than its inner protoplanetary disk. She suggests that it might be time to reexamine that object with JWST for a more in-depth analysis.

As for HOPS-315, McClure speculates that the system may yet reveal further surprises. Her team’s JWST data indicate that the outflow jet, which initially complicated their analysis, is notably deficient in silicon—the key element for forming the silicates that are essential for planetary formation. Perhaps, she muses, rather than contributing to the jet, the silicon has been sequestered in deeper parts of the disk, possibly in dust reservoirs or larger rocky bodies.

“Our findings imply that about 98 percent of the expected silicon relative to the carbon we observe in the jet is absent,” she notes. “This could hint at the already ongoing formation of planetesimals in a manner similar to what must have occurred in our own solar system.”