For the first time, astronomers have caught a glimpse of a solar system just as it begins to form, spotting the first tiny seeds that will one day grow into planets taking shape around a distant baby star.
It’s the earliest stage of planet formation ever observed, offering a glimpse of what our own Solar System might have looked like shortly after the Sun first flickered into life.
“While we have seen signs of planet formation – the growth of tiny dust grains into slightly larger dust grains – in several systems, in this system we are seeing an earlier step: the formation of some of the solids that will become tiny grains,” Prof Merel van ‘t Hoff, a co-author of the new study detailing the findings, told BBC Science Focus.
“You could compare it to a researcher studying human evolution who, so far, had only seen toddlers, and now, for the first time, sees a baby.”
The baby planetary system is bursting into life around a young star known as HOPS-315, located 1,300 light-years away from Earth.
The star is thought to resemble our own Sun in its earliest stages, making it an ideal candidate for uncovering clues about how the Solar System – and ultimately Earth – began.
Young stars like HOPS-315 are surrounded by hot discs of gas and dust known as ‘protoplanetary discs’. Initially, these discs are so hot that elements like silicon and iron – the building blocks of planets – are a gas. But as the disc cools, they begin to solidify.
Evidence from ancient meteorites in our own Solar System suggests that the first solid material to cool and condense from these discs is crystalline minerals containing silicon monoxide (SiO).
Using the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA), the international team detected SiO in both its gaseous form and as part of newly formed crystalline minerals around HOPS-315. This strongly suggests that solidification has only just begun.
“These first little bits of minerals we’re seeing will stick together to form ‘pebbles’ – rocky chunks about the size of a thumbnail,” Prof Melissa McClure, who led the study, told BBC Science Focus. “Once you get enough of them clustered close together, they can spontaneously collapse under their own gravity to form kilometre-sized asteroid-like bodies.
“Those eventually collide and go on to form the embryos of planets, then full-size rocky planets and even the cores of planets like Jupiter.”
The team plans to continue observing HOPS-315 while also searching for other systems caught at this earliest stage of planetary evolution.
But don’t expect to watch a planet form in real time. As van ‘t Hoff noted, “the timescale at which the disc evolves will be hundreds of thousands of years.”
Read more:
- Groundbreaking study could reveal secrets of how planets are born
- Astronomers spot first direct evidence of planet forming
- The Solar System: How do we know how it formed?
About our experts
Merel van ’t Hoff is an assistant professor at Purdue University, US. Her research aims to understand how planets form and how prevalent planets like Earth might be in the Milky Way and other galaxies. Before joining Purdue, Prof. van ‘t Hoff was a postdoctoral researcher in the Michigan Society of Fellows at the University of Michigan.
Melissa McClure is an assistant professor and Veni Laureate at Leiden Observatory in the Netherlands. Her research uses observations and models to trace how the solid building blocks of life (icy and rocky “dust” grains) evolve from their origins in dense molecular clouds to their incorporation into planetesimals and young protoplanets embedded within protoplanetary discs.