A stellar nursery 1,000 light-years away has produced objects so small that the boundary between stars and planets is becoming increasingly difficult to define.

Deep observations from the James Webb Space Telescope have revealed brown dwarfs in the star-forming region IC 348 with estimated masses of only about twice that of Jupiter. That equals roughly 0.19% of the Sun’s mass and pushes observations into a range where theories struggle to explain how objects can form through the same process that makes stars.

The findings were published in The Astrophysical Journal Letters. They build on earlier Webb observations of IC 348 that uncovered brown dwarfs between three and four Jupiter masses.

The new observations went deeper. Along with the extraordinarily small brown dwarfs, astronomers found evidence for a disk around one of them and an unexplained hydrocarbon signature in the atmospheres of the coolest objects.

IC 348 lies in the constellation Perseus and contains hundreds of young stars surrounded by the remnants of the molecular cloud that created them.

Stars form when cold clouds of molecular hydrogen collapse under gravity. As the material contracts, the center becomes hot and dense enough for nuclear fusion to begin.

Brown dwarfs start in much the same way but never accumulate enough mass to sustain ordinary hydrogen fusion. The smallest true stars contain roughly 8% of the Sun’s mass, leaving brown dwarfs below that boundary.

The unresolved question is how far downward this star-like formation process can continue.

Astronomers do not simply classify every Jupiter-mass object as a planet. Formation matters. Planets are generally expected to assemble within disks surrounding stars or other objects, while brown dwarfs form more directly from collapsing clouds.

Finding free-floating brown dwarfs with only a few Jupiter masses therefore probes the minimum mass that gravitational collapse can produce.

The same research team investigated IC 348 with Webb in 2022 and found three exceptionally low-mass brown dwarfs. The lightest had an estimated mass between three and four Jupiters.

Astronomers returned with Webb’s Near-Infrared Camera, or NIRCam, in 2024 to survey a much larger region and search for still fainter objects.

Brown dwarfs radiate strongly at infrared wavelengths while they are young, making Webb particularly well suited to finding them.

The team selected candidates according to their colors and brightness. In 2025, Webb’s Near-Infrared Spectrograph, or NIRSpec, was used to obtain spectra and determine whether the candidates showed the characteristics expected from young brown dwarfs.

The deepest observations reached objects with estimated masses around two Jupiters. They are now regarded as the least massive brown dwarfs identified with spectral evidence.

The result moves the observational boundary of star formation into a range normally associated with giant planets.

One of the discoveries raises an even more unusual possibility.

A newly identified object with an estimated mass near two Jupiters shows excess infrared emission associated with a surrounding disk. Such disks contain the gas and dust from which planets can potentially assemble.

That means an object roughly comparable in mass to a large planet may itself possess the raw material needed to build smaller companions.

The distinction is important. A planet orbiting this brown dwarf would form through a different process from the brown dwarf itself, even though both could occupy overlapping mass ranges.

The observation demonstrates why mass alone cannot always distinguish planets from brown dwarfs. Their origins and environments also matter.

Whether the disk around this exceptionally small object will actually produce planets remains unknown. Detecting a disk establishes that material is present, not that planet formation is occurring or will succeed.

The spectra contained another surprise.

Researchers detected an absorption feature near 3.4 micrometers that they attribute to an unidentified aliphatic hydrocarbon, a molecule containing hydrogen and carbon.

This chemical signature had appeared in earlier Webb observations of the lowest-mass members of IC 348. The newer observations showed that the feature continues among extremely cool newborn brown dwarfs.

It does not behave as expected from standard brown-dwarf atmosphere models. Methane would normally become increasingly important as brown dwarfs cool, yet these objects instead display a different hydrocarbon signature.

The pattern has become distinctive enough that the researchers proposed a new spectral class called “H,” with the letter referring to hydrocarbon.

Astronomers traditionally classify very cool objects into L, T and Y spectral classes according to changes in their atmospheric chemistry and spectra. An H class would identify a population of young brown dwarfs whose spectra are dominated by this previously unexplained 3.4-micrometer feature.

More examples will be needed before astronomers can establish detailed subclasses or determine exactly what molecule is responsible.

IC 348 is becoming an unusually powerful laboratory for testing where star formation ends.

The new brown dwarfs suggest that collapsing molecular clouds can produce objects with masses comparable to giant planets. Yet exactly how such tiny fragments avoid gathering more material remains difficult to explain.

The growing census also gives astronomers a better way to measure the lower end of the initial mass function, which describes how frequently stars and brown dwarfs of different masses form.

Even smaller candidates may be waiting in the Webb data. Some objects without spectroscopic confirmation appear faint enough to approach Jupiter’s mass, although spectroscopy will be necessary before astronomers can determine whether they truly belong to IC 348.

For now, the confirmed objects have already shifted the question. Astronomers are no longer asking whether star formation can reach planetary masses. They are trying to determine just how far into that territory it can go.

These studies explore IC 348, free-floating planetary-mass objects and competing ideas for how extremely small brown dwarfs can form.