Evrim Yazgin
Cosmos science journalist
For the first time, astronomers have identified the earliest moment when planets started forming around a star.
The discovery, detailed in a paper published in Nature, was made possible by observations from the European Space Observatory’s (ESO) Atacama Large Millimeter Array (ALMA) telescope in Chile and the James Webb Space Telescope (JWST).
The star, HOPS-315, is a “proto” or “baby” star about 1,300 light-years from Earth. Discs of gas and dust, known as “protoplanetary discs”, orbit around such young stars and are believed to be the swirling sources of matter which eventually clumps together to form planets.
Astronomers have previously seen newborn exoplanets – hot, massive, Jupiter-like gas giants – but lead author and professor at Leiden University in the Netherlands, Melissa McClure, says: “We’ve always known that the first solid parts of planets, or ‘planetesimals’, must form further back in time, at earlier stages.”
Co-author Merel van ‘t Hoff, a professor at Purdue University, USA, says the find is like “seeing a system that looks like what our solar system looked like when it was just beginning to form”.
Material from the beginning of our own solar system is trapped within ancient meteorites. These meteorites have been dated to more than 4.6 billion years ago, and they contain high levels of crystalline minerals with silicon monoxide (SiO).
The first planetesimals would have been on the scale of kilometres and would have formed after these SiO-rich minerals condensed out of the gas disc.
Condensation of these crystalline minerals is exactly what the astronomers looking at HOPS-315 found, pointing to the formation of the first planetesimals in the system.
“This process has never been seen before in a protoplanetary disc – or anywhere outside our solar system,” says co-author Edwin Bergin, a professor at the University of Michigan, USA.
HOPS-315 is a prime candidate for further study to see in real-time the processes which led to the formation of our own solar system.
“I was really impressed by this study, which reveals a very early stage of planet formation,” says ESO astronomer and European ALMA programme manager Elizabeth Humphreys, who did not take part in the study. “It suggests that HOPS-315 can be used to understand how our own Solar System formed. This result highlights the combined strength of JWST and ALMA for exploring protoplanetary discs.”