The youngest planet ever found is less than a million years old

A protoplanetary disk around a star 450 light-years away holds a planet that should not exist yet. Elias 2-24 b is less than a million years old — the youngest confirmed planet known, beating the previous record by at least four million years. It orbits at 55 AU from its host star, more than ten times Jupiter’s orbital distance from the Sun, in a region where current models give planets far more time than this one has had.

The system sits inside the ρ Ophiuchi cloud complex, one of the most active star-forming regions visible from Earth. Its youngest stellar populations are under a million years old, setting the upper bound on Elias 2-24 b’s age. The planet is still actively accreting gas and dust from its surrounding disk — astronomers caught it mid-formation, at the moment it was still growing into what it will eventually become.

How they found a planet hidden in archival data

The discovery came from reanalyzing Keck Observatory images that had never been fully processed. Andrea Bernardi, a doctoral candidate at Universidad Diego Portales in Chile, applied new imaging techniques to archival data from Keck’s NIRC2 coronagraph and found a faint signal consistent with a planet-mass companion sitting inside a gap in the disk. Additional Keck observations, combined with independent data from the ALMA millimeter-wave telescope and the European Southern Observatory’s Very Large Telescope, confirmed the object was gravitationally bound to the star and moving with it.

The planet sits precisely inside a gap in Elias 2-24’s protoplanetary disk — the concentric ring-and-gap structure familiar from radio images of young stellar systems. The standard interpretation of such gaps is that a forming planet sweeps material clear along its orbit. Elias 2-24 b is now the youngest direct confirmation that this mechanism works as theorists proposed. “We’re able to observe a stage of planet formation that is rarely seen directly,” Bernardi said.

The distance problem

At 55 AU from its host star — roughly where the outer Kuiper Belt sits in our Solar System — Elias 2-24 b runs into direct conflict with the dominant theory of giant planet formation. Core accretion builds planets from solid cores that slowly accumulate rock and ice before growing massive enough to capture gas from the disk. At Jupiter’s orbital distance of roughly 5 AU, this process takes several million years under standard models. At 55 AU, disk material is far sparser and orbital periods far longer; core accretion predicts formation timescales extending to tens of millions of years at these distances.

Elias 2-24 b, at under a million years, does not fit that picture. The alternative — disk instability, where a gravitationally unstable region of the disk collapses directly into a planet on a timescale of thousands of years — could in principle produce a planet this young. But disk instability typically forms more massive objects, and the boundary between a Jupiter-mass planet and a brown dwarf is precisely where predictions are least reliable. Co-author Alice Zurlo noted that theoretical models “still struggle to reliably predict its mass, entropy, and expected luminosity” for an object at this evolutionary stage. Lucas Cieza, who co-supervised the project, was direct: “Elias 2-24 b shows us that even our best planet-formation models are still missing some important processes.”

What remains unsettled

The planet’s classification as a giant planet rather than a brown dwarf or disk clump rests on its orbital motion: the team tracked Elias 2-24 b across multiple epochs over several years, confirming it is gravitationally bound to the star and not a background object. Its mass has not been directly measured. Current estimates derive from luminosity and evolutionary models — the same models Zurlo cautions are uncertain for objects this young.

Which formation mechanism produced it remains an open question. Disk instability, unusually favorable conditions that accelerated core accretion, or some process the models have not yet incorporated — Elias 2-24 b does not currently distinguish between them. One independent uncertainty is the star’s own age. The under-one-million-year estimate is anchored to membership in the ρ Ophiuchi cloud; if the star sits at the older end of that population’s age range, the planet’s confirmed age increases proportionally. Constraining the star’s age is as important to this result as any further imaging of the planet itself.

Common questions about Elias 2-24 b

What was the previous record for the youngest confirmed planet? PDS 70 b, confirmed through direct imaging and published in 2018, held the benchmark at approximately 5 million years old. Elias 2-24 b beats that by at least 4 million years under current age estimates.

Can a planet form in under a million years? Under disk instability — where a region of the disk collapses gravitationally rather than building from a small core — formation timescales of thousands to tens of thousands of years are theoretically possible. Whether that is what happened at Elias 2-24 is the central question the discovery opens.

What is a protoplanetary disk gap and why does it matter? Disk gaps are ring-shaped clearings in the gas and dust around young stars, visible in radio images from ALMA. The standard interpretation is that a forming planet sweeps material along its orbit as it grows. Elias 2-24 b sitting inside a gap at under a million years old is direct evidence of that gap-carving process — something previously inferred from the gaps themselves but never directly observed this early in a planet’s life.

Will Webb observe this system? The James Webb Space Telescope’s mid-infrared instruments are suited to measuring the thermal emission of a young planet still embedded in disk material. The ρ Ophiuchi cloud complex is already a high-priority target for planet formation science; dedicated JWST follow-up observations of Elias 2-24 b are a natural next step.

Bernardi’s team at Universidad Diego Portales is planning multi-wavelength follow-up observations to constrain the planet’s spectral energy distribution. That will place tighter limits on its mass and allow a direct comparison against formation models — testing whether disk instability, core accretion, or something else is consistent with a giant world at 55 AU in under a million years. The initial Keck data was gathered in 2018 and confirmed with VLT and ALMA over the following years; the paper appeared in The Astrophysical Journal Letters in September 2026. The result, whatever it ultimately shows, will either close the gap in our understanding of how planets form — or widen it.

Reference: Bernardi et al., “Direct Imaging Confirmation of a Protoplanet Candidate in the Elias 2-24 Disk,” The Astrophysical Journal Letters, 2026. DOI: 10.3847/2041-8213/ae9bb6

Tags: astronomy, planet formation, protoplanetary disk, Andrea Bernardi, Elias 2-24 b, Keck Observatory