Somewhere in the constellation Taurus, 450 light-years from where you’re sitting, a disc of gas and dust is doing what it has done for millions of years: slowly, grain by grain, building a world. The difference now is that we can finally see it happening.
On 3 April 2026, the European Space Agency released its latest Webb Picture of the Month: a pair of protoplanetary discs captured edge-on by the James Webb Space Telescope. The two targets, Tau 042021 in Taurus and Oph 163131 in Ophiuchus, are among the most detailed views ever taken of the places where planets are born.
What makes these images extraordinary is the angle. Both discs happen to be oriented edge-on to our line of sight, which blocks the blinding glare of the young star at each centre. With that light out of the way, Webb’s instruments can read the disc itself: its structure, its chemistry, even the sizes of the dust grains drifting through it. It is the difference between staring into a spotlight and studying the lampshade.
Two discs, two stories
Tau 042021 (catalogue designation 2MASS J04202144+2813491) orbits a young star roughly 0.4 times the mass of our Sun. Its disc stretches about 1,000 astronomical units in radius, making it one of the largest protoplanetary discs known in any nearby star-forming region. In the image, it appears as a dark horizontal band flanked by broad, colourful cones of scattered light, with a narrow jet punching straight out from the star’s poles.
The reds, oranges, and greens in those cones are not artistic choices. They map to real physical properties: different sizes of dust grains and the signatures of molecules like molecular hydrogen (H2), carbon monoxide (CO), and polycyclic aromatic hydrocarbons (PAHs). Earlier studies using Webb’s MIRI spectrograph even detected water vapour and CO emission extending 90 to 190 AU from the star, far beyond the distances where such hot molecular signatures were expected.
Its companion in the image, Oph 163131 (2MASS J16313124-2426281), sits about 480 light-years away. Where Tau 042021 appears symmetrical and expansive, Oph 163131 is more compact, with purple scattered-light lobes above and below a yellow dusty core. And buried in that core is a clue: data from the Atacama Large Millimeter/submillimeter Array (ALMA) reveals a gap in the inner disc. Something has swept the dust aside. That something, researchers believe, may already be a planet in the making.
Why edge-on matters
Most protoplanetary discs we observe are tilted toward us, which makes them look like flat rings or bright smudges. An edge-on orientation is rarer and far more revealing. It lets astronomers measure how dust grains settle toward the midplane over time, a process called vertical settling, which is one of the earliest steps in planet formation. When grains settle, they collide more often, stick together, and gradually build the pebble-sized bodies called planetesimals.
In Tau 042021, Webb found that 10-micrometre grains remain well mixed from the disc surface all the way down to the midplane in the outer regions. That tells us the outer disc is still turbulent, still stirred up, while the inner regions may already be further along in the settling process. In Oph 163131, the ALMA gap suggests the inner disc has progressed even further: enough material has accumulated for a protoplanet to carve its own corridor through the dust.
These two discs, observed as part of Webb programme #2562 (led by François Ménard and Karl R. Stapelfeldt), sit at different stages of the same process. Together, they offer something like a time-lapse of how a stellar nursery graduates from raw material to a planetary system.
What comes next
The observing campaign behind these images is ongoing. Programmes #2562 and #4290, spanning Webb’s Cycles 1 and 2, are targeting several more of the largest edge-on discs in nearby star-forming regions. Future observations will push deeper into the mid-infrared, where Webb’s MIRI instrument can trace the thermal glow of larger grains and the chemical fingerprints of ices that may one day become the water on a rocky world’s surface.
Researchers including Marion Villenave, Gaspard Duchêne, Christophe Pinte, and their collaborators are already analysing additional wavelength data that may reveal whether the gap in Oph 163131 truly marks a forming planet, or whether some other mechanism (a companion star, a gravitational instability) is responsible. If confirmed, it would be among the youngest protoplanets ever identified, caught in the act of clearing its own orbit.
Four and a half billion years ago, our own world began as a smear of dust inside a disc like these. We are looking, for the first time with this kind of clarity, at the opening chapter of a story we already know the ending to.
