Birth of Planets: JWST Spots Hot Mineral Condensation in a Proto-Stellar System

In a recent episode of SETI Live, SETI Institute Deputy Director Dr. Simon Steel spoke with astronomer Dr. Melissa McClure of Leiden University about a groundbreaking discovery: the earliest stages of planet formation caught in action.

Using data from the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA), Dr. McClure’s team identified silicon monoxide (SiO), a key indicator of vaporized rock, in the young stellar object HOPS-315, located roughly 1,300 light-years away in the Orion Molecular Cloud. This finding, published in Nature, marks the first direct evidence of hot mineral condensation in a protoplanetary system at such an early stage.

A Protostar in Orion

HOPS-315 belongs to a cluster of young stars in Orion, an active nursery of stellar birth. Most protostars in this region remain shrouded by dense clouds of gas and dust, but this particular system is positioned at an angle that allows an unobstructed view toward its center.

ALMA’s high-resolution radio wavelength imaging revealed an hourglass-shaped outflow of gas, carved by twin jets launched from the star’s poles. These jets are powerful streams of hot gas, around 3,000 Kelvin, expelled as material accretes onto the protostar. The system’s geometry offers a rare opportunity to peer into the zone where planets begin to form.

JWST Detects Vaporized Rock

While ALMA mapped the large-scale structure of HOPS-315, JWST zoomed in on the region surrounding the star itself. In its infrared spectra, the telescope detected both crystalline silicates–minerals such as forsterite (a magnesium silicate similar to the gemstone peridot)–and a distinct band of silicon monoxide (SiO) gas.

Silicon monoxide forms when solid silicate minerals are heated until they sublime (transition directly from the solid to the gas phase). In this case, Dr. McClure’s team inferred that interstellar dust grains are migrating inward toward the star, reaching temperatures around 1,200 Kelvin. At this threshold, they vaporize into SiO gas, which then cools and recondenses into crystalline minerals – the building blocks of rocky planets.

The Pebble Stage: Seeds of a Planetary System

This process represents what researchers often call t = 0 in solar system formation, the first appearance of solid material that can eventually accrete into larger bodies. As the silicon monoxide gas cools, it produces millimeter- to centimeter-sized mineral pebbles. These solids may collect in dense regions of the disk, known as pebble traps, and collapse into planetesimals—the precursors to asteroids and terrestrial planets.

Dr. McClure explained that similar inclusions found in meteorites on Earth have been dated to define the very beginning of our own Solar System’s formation timeline. The same mechanisms appear to be at work around HOPS-315, offering a direct glimpse of how planetary systems like ours begin.

Clues to Earth’s Origins

Beyond observing a single system, McClure’s team aims to identify more objects like HOPS-315 to compare how mineral compositions vary over time. Variations in the isotopic makeup of these early solids could help explain some of the unresolved questions in planetary science – such as the missing isotopic components needed to match Earth’s precise elemental ratios.

The team hypothesizes that systems like HOPS-315 may produce these “missing” minerals, providing the final ingredients that formed Earth’s crust and mantle.

Technical Frontiers: JWST and ALMA in Tandem

This study pushes the capabilities of both JWST and ALMA to their limits. ALMA’s millimeter-wave data revealed the cold, large-scale environment of the disk, while JWST’s infrared spectroscopy traced the hotter inner regions near the protostar. Coordinating such observations required global collaboration and meticulous scheduling across multiple time zones and telescope proposal cycles. 

With a central star of about 0.6 solar masses, expected to grow to one solar mass within a million years, HOPS-315 resembles the Sun in its infancy. The discovery demonstrates how JWST and ALMA, together, can reveal not just the chemistry but also the physical mechanisms behind the birth of planets.

Upgrades to ALMA in the next decade may improve its sensitivity to find faint gas lines in its spectra, enabling even sharper views of these dynamic systems. Until then, HOPS-315 stands as one of the most detailed examples of the moment when dust becomes rock, and rock becomes the seed of a planet.

Dr. Steel concludes that observing such systems gives scientists “a snapshot in time” of the processes that shaped our own Solar System. By capturing this formative moment, researchers can trace the steps from vaporized dust to habitable worlds.

Watch the whole SETI Live conversation with Dr. Simon Steel and Dr. Melissa McClure here, and read the paper here.