Astronomers caught a star system at the moment when solid grains began to form planets. This snapshot reveals how planets first start to form, just as Earth once did.

The infant star HOPS-315 sits about 1,300 light-years, roughly 7.6 quadrillion miles, away in the constellation Orion. Around it whirls a disc of gas and dust where heat is high enough to bake rock yet cool enough for those rocks to re-form.

Melissa McClure of Leiden University led the international team that pieced together these first moments of planetary assembly. Their finding gives researchers a live laboratory that mirrors the opening chapter of the Solar System’s own story.

How planets form from early solids

In primitive meteorites, tiny calcium-aluminum-rich inclusions tell us that the Solar System’s clock started ticking 4.567 billion years ago. Those inclusions condensed from a searing vapor and seeded every terrestrial planet we know.

Because the clock starts with condensation, catching that step beyond the Sun has been an astronomer’s white whale.

The new observation marks the first time any telescope has seen gas-phase silicon monoxide (SiO) alongside freshly crystallizing silicates in the same patch of a protoplanetary disc.

McClure’s team spotted the minerals within an orbit comparable to our asteroid belt. That match matters, for it pins early chemistry to a region that later fed Earth with water and metals.

Crystals forming around HOPS-315

The James Webb Space Telescope (JWST) collects infrared light that pierces the dust cocoon shrouding HOPS-315, revealing the distinct fingerprint of hot SiO molecules. Those molecules glow at about 2,200°F, a temperature that vaporizes most common rocks.

ALMA, the Atacama Large Millimeter/submillimeter Array, then measured the same region at millimeter wavelengths and mapped where the glow comes from.

By combining the two views, scientists confirmed that both gas and solid forms of silicon occupy a ring no farther than 2 astronomical units from the star.

Handling these observations is tricky because HOPS-315 also drives a jet rich in SiO. The team disentangled the jet’s signal from the disc’s by checking velocities, the jet gas races outward, whereas disc material orbits sedately.

A final check involved comparing the brightness of different SiO lines. The ratio matched laboratory predictions for vapor that is actively condensing, adding yet another layer of confidence to the result.

Planets forming from gas and crystals

Crystalline silicates appear where cooling vapor meets a sharp fall in temperature. The presence of both phases at one location means condensation is happening right now, not long ago nor far away in another part of the disc.

“This process has never been seen before in a protoplanetary disc, or anywhere outside our Solar System,” said Edwin Bergin of the University of Michigan, a co-author on the study.

He adds that the minerals are the same kind locked inside 4.5-billion-year-old meteorites on Earth’s shelves.

This is HOPS-315, a baby star where astronomers have observed evidence for the earliest stages of planet formation. Together with data from the James Webb Space Telescope (JWST), these observations show that hot minerals are beginning to solidify. In orange we see the distribution of carbon monoxide, blowing away from the star in a butterfly-shaped wind. In blue we see a narrow jet of silicon monoxide, also beaming away from the star. These gaseous winds and jets are common around baby stars like HOPS-315. Click image to enlarge. Credit: ALMA(ESO/NAOJ/NRAO)/M. McClure et al.

“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 co-author, Logan Francis from the Advanced Functional Fabrics of America (AFFOA).

He notes that the condensation zone sits at almost the same orbital radius as our asteroid belt.

The mineral grains measure less than a micrometer across, yet they mark the first step toward kilometer-scale planetesimals. Electrostatic forces will make them clump for thousands of years until gravity takes over.

HOPS-315 mirrors Earth’s origins

Laboratory studies show that minerals rich in silicon and oxygen condense first, followed quickly by iron-nickel alloys and then more volatile compounds.

Seeing hot SiO vapor around HOPS-315 hints that a similar chemical parade is marching there.

By estimating the star’s luminosity and the disc’s temperature gradient, McClure’s group concludes that crystalline silicates could mass about a tenth of the Moon. That is plenty to seed multiple rocky planets if subsequent growth is efficient, as models suggest.

Isotopic work on chondrules indicates that the earliest building blocks in our own Solar System formed within the first million years, a timescale now testable in real time with HOPS-315.

Matching astronomical data to isotope chronometers promises a much sharper picture of planet formation than meteoritic studies alone.

The discovery may also shed light on why Earth contains less carbon than nebular models predict. If early minerals trap oxygen and silicon immediately, carbon may remain gaseous longer and get pushed outward before it can join newborn worlds.

What’s next in watching planets form

Over the next year, ALMA will return to HOPS-315 to look for water ice farther out in the disc.

If water lines up beyond the silicate ring, astronomers can test whether rocky seeds migrate inward before they acquire ice mantles, a step that may explain why Earth ended up with oceans.

JWST will track how the SiO signature evolves. A steady decline would show vapor freezing out, whereas a surge could hint at heating bursts from magnetic flares or spiral shocks.

Witnessing the dawn of a new solar system. Credit: ESO

Beyond the specifics of HOPS-315, the result boosts confidence that rocky planets are common. If condensation begins so early, many stars may launch planet formation well before their gas discs disperse, leaving time for worlds to migrate, collide, and settle into stable orbits.

Astronomer Elizabeth Humphreys at ESO, who was not involved in the study, said she was “really impressed” that the team could pinpoint the first solids.

She argues that the synergy of Webb and ALMA is revealing a Universe “in which the steps toward life-bearing planets start earlier than we dared hope.”

The study is published in Nature.

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