A green and gold cloud stretches across the image, dotted with stars, while two bluish jets shoot out in the top right-hand corner. This spectacular view of IC 348, published on 15 September 2026, comes from the James Webb Space Telescope. It shows a region where stars are being born, about 1,000 light-years away in the constellation of Perseus.
But the image tells a less visible story than its colours: researchers have identified brown dwarfs with masses as low as about twice that of Jupiter. These objects are too light to become ordinary stars, and challenge astrophysicists to pin down the lower limit of star formation.
IC 348: a stellar nursery on a cosmic scale
IC 348 is a young star cluster in a region rich in gas and dust. NASA estimates its age at about five million years—a very short time compared with the billions of years that many stars live.
Stars are born in cold clouds of gas, mainly molecular hydrogen. Under gravity, some regions become dense enough to collapse. They can form a protostar, surrounded by matter that continues to fall towards it and sometimes by a disc of gas and dust.
If the central object accumulates enough mass, its core reaches the temperatures and pressures needed to sustain the fusion of hydrogen into helium. It then becomes a star. If its mass remains too low, this sustained process does not get going.
In this region, Webb is studying not only forming stars but also the smallest objects arising from the same clouds, which are difficult to distinguish at great distances.
A brown dwarf: neither an ordinary star nor simply a planet
Brown dwarfs occupy a fascinating space between small stars and giant planets. Their mass is not enough to sustain the fusion of ordinary hydrogen, as happens in a main-sequence star. Some can, however, briefly undergo reactions involving deuterium, a heavier form of hydrogen.
Studying them raises a question of terminology. A giant planet can have several times Jupiter’s mass; a very low-mass brown dwarf can too. Mass alone does not tell us how an object formed.
A star or brown dwarf can form from the collapse of a gas cloud. A planet generally forms in a disc around a star. Some planets can later be ejected from their systems and drift alone through space.
Distinguishing between these pathways therefore means looking at the context, the properties of the star cluster, the estimated age, any discs and formation models. The new objects in IC 348 are being studied as very low-mass brown dwarfs; their existence is prompting scientists to test just how low the mass of an object formed through a stellar process can be.
Why do two Jupiter masses surprise researchers?
Models of star formation describe the collapse of part of a cloud under its own gravity. Yet the smaller the mass involved, the weaker the available gravity.
For a very low-mass region of gas, it becomes harder to explain how it could contract to form an independent object rather than disperse. This is the difficulty highlighted by research on IC 348.
In December 2023, an initial study using Webb identified free-floating objects with masses of three to four Jupiters in the same cluster. The deeper observations presented in 2026 reach down to about two Jupiter masses, or 0.19% of the Sun’s mass, according to NASA and ESA.
One qualification is important: these masses come from the interpretation of observations and astrophysical models, not from weighing the objects on a set of scales. The result opens up a new range of masses to explore, without demonstrating that all models of star formation are wrong.
Why can James Webb detect these very faint objects?
Young brown dwarfs are still relatively hot after forming. As they cool, they become dim in visible light, but can be studied through their infrared radiation.
James Webb has instruments specifically sensitive to this part of the spectrum. In 2024, the science team used its NIRCam camera to identify candidates based on their brightness and infrared colours.
The second step took place in 2025, using the NIRSpec spectrograph. Breaking down the light makes it possible to look for signatures associated with the objects’ temperature, chemical composition and properties.
This sequence is essential to understanding the announcement: a bright spot in an image is not enough to identify a brown dwarf. Images identify candidates, then spectral analysis helps researchers distinguish what they are and estimate their properties.
The measurements were taken in 2024 and 2025. 15 September 2026 marks the public release of the wide panorama and its scientific interpretation, not the date the image was taken.
The colours in the image are not what the eye would see
The image released by NASA shows large green and yellow areas, filaments and bluish jets. These hues are the result of scientific and visual processing.
NIRCam records light through several near-infrared filters. In the 2026 panorama information sheet, data from the F162M and F182M filters are assigned to blue, F360M to green, and F444W to red. These visible colours bring together observations taken in different radiation bands.
It is therefore not a colour photograph of the kind an ordinary camera would take. The processing helps to reveal the structures, but does not provide a direct reproduction of human vision.
The long spikes around some stars also have a technical explanation: they are diffraction spikes, caused by the telescope’s optics. They do not represent physical rays coming out of each star.
For further details, NASA has published the original view of IC 348, with its filters and acquisition date.
In the top right, newborn stars are shooting out jets
The most spectacular objects in the top right-hand corner are not necessarily the brown dwarfs being sought. They are young protostars whose jets of matter strike the surrounding gas and dust.
These impacts create bright regions called Herbig–Haro objects. NASA identifies HH 797 in particular, which appears as a long, almost horizontal structure. Analysis reveals that it is actually produced by two protostars generating almost parallel jets.
A little further away, HH 211 has a shape reminiscent of a propeller, associated with narrow jets and broader outflows. These structures make it possible to study the exchange of matter and energy during the earliest stages of a star’s birth.
Thus, a single image contains several stages and several types of object: cold clouds, young stars, forming protostars and brown dwarfs too light to sustain the ordinary fusion of hydrogen.
A disc around a tiny brown dwarf
One of the smallest brown dwarfs in the new study shows evidence consistent with the presence of a disc of matter around it.
This is an intriguing observation: discs can play a role in the birth of smaller bodies. Researchers are therefore asking whether an object with a mass itself close to that of a giant planet could form very small planets.
This is not a discovery of confirmed planets around this brown dwarf. The presence of a disc remains a clue that needs further investigation. Other measurements and analyses would be needed to demonstrate the existence of a planetary companion.
A chemical signature that remains mysterious
Spectroscopic observations also reveal a signature attributed to a hydrocarbon—a molecule made of carbon and hydrogen—that has not yet been precisely identified.
This feature had already been noted in earlier studies of very small brown dwarfs. Atmospheric models do not yet perfectly reproduce all the measured signatures.
The new campaign provides additional objects for comparison. However, finding a chemical clue is not enough to announce that a new molecule has been identified, or that a new astrophysical class has been officially recognised.
What astronomers want to learn next
The observations are part of Webb programme GO 4866, dedicated to exploring the lowest masses produced by the processes of star formation.
Researchers want to compare populations of objects in several star-forming regions. A cluster such as IC 348 has its own age, environment and mass distribution. Other regions will need to be studied to understand what is due to a general process and what depends on local conditions.
The central question is easy to put into words, but difficult to answer: what is the smallest object that can be born as a star? The panorama released on 15 September 2026 does not yet offer a definitive answer. It provides new observations, very low-mass candidates and avenues for future research.
Sources and scientific images
- NASA, 15 September 2026: panorama of IC 348 and brown dwarfs with two Jupiter masses.
- ESA/Webb, presentation of the discovery and spectroscopic results.
- NASA, information sheet for the new 2026 image: date, filters and credits.
- NASA, December 2023: first search for the smallest brown dwarfs in IC 348.
- NASA, Webb feature: the birth of stars and planetary systems.
- NASA, annotated panel of structures in the IC 348 region.
