A brand-new cosmic process has been added to the collection of special moments witnessed in science: a team of astronomers captured the first specks of planet-forming material, hot minerals just beginning to solidify, around an infant star called HOPS-315. “For the first time, we have identified the earliest moment when planet formation is initiated around a star other than our sun,” said Melissa McClure, team leader and Leiden University researcher.
The findings were published on July 16 in the journal Nature. The momentous event was spotted with the help of two telescopes working together: the Atacama Large Millimeter/ submillimeter Array (ALMA), an arrangement of 66 radio telescopes found in Chile’s Atacama Desert, and NASA’s James Webb Space Telescope (JWST).
The astronomers used JWST to identify hot planet-forming crystalline minerals just starting to condense and solidify around HOPS-315, a ‘proto’ or baby star about 1,300 light-years away from us. To get a closer look at where exactly the signals were coming from, they observed the system with ALMA and beheld a dense disk of matter around a young star, where clumps of gas and dust collapse into larger objects like planets.
“Then that unlocked everything,” said Edwin Bergin, study co-author and a University of Michigan star formation specialist. He noted that it’s the first time that planet-forming solids have ever been detected, which could help researchers better understand how our own Solar System was born.
HOPS-315 is analogous to the nascent Sun, the star of our Solar System, when the Solar System was being formed. Stars are born due to heat from friction when cold high-density molecular clouds of dust and gas collapse under their own gravity as they collide with each other, collect matter, and gain mass. Usually, surrounding baby stars like this, astronomers observe swirling disks of dust and gas (the same material that formed the protostar) called ‘protoplanetary disks,’ the birthplaces of new planets. Although astronomers have already seen massive Jupiter-like planets in such young disks, McClure said, “We’ve always known that the first solid parts of planets, or ‘planetesimals’, must form further back in time, at earlier stages.”
Back in our Solar System, the very first of these solid materials to condense near Earth’s present location, when it was taking shape about 4.6 billion years ago, is observed to be trapped within its ancient meteorites, full of crystalline minerals containing silicon monoxide (SiO), which could condense at extremely high temperatures found in young planetary disks. Then, these newly condensed solids bind together over time, forming planets as they gain size and mass.
Fast forward to their new discovery, astronomers have spotted evidence of these very minerals starting to condense in the disk around HOPS-315. Their results show that SiO is present in its gaseous state around HOPS-315 and in these hot crystalline minerals, implying that it is just beginning to solidify. “This process has never been seen before in a protoplanetary disc — or anywhere outside our Solar System,” said Bergin.
“We’re really seeing these minerals at the same location in this extrasolar system as where we see them in asteroids in the Solar System,” said Logan Francis, team member and Leiden University researcher.
The discovery provides a glimpse into the earliest stages of planet genesis or formation around a star, possibly giving rise to a new planetary system, just like our home planetary system, the Solar System. Additionally, it brings forth an opportunity for researchers to investigate the origin of these extrasolar planets or “exoplanets” and the significance of planet-forming material to planet genesis. It could potentially give clarity on how our own Solar System became what it is today. According to Bergin, the researchers are hoping to use ALMA again to probe other similar young star systems.
“We’re seeing a system that looks like what our Solar System looked like when it was just beginning to form,” said Merel van ‘t Hoff, team member of Purdue University. “This system is one of the best that we know to actually probe some of the processes that happened in our Solar System.”
