The scale resolution opened
When a planet-forming disk shines across only a few astronomical units, its face can look smooth from far away. The peer-reviewed observation by Pietro Curone and colleagues, published October 14, changes the scale at which that impression is tested. ALMA resolved 11 small disks in Lupus at a wavelength of 0.9 millimetres and a resolution of roughly two astronomical units. Taking the Earth–Sun separation as one unit, the measurement probes dust in the immediate neighbourhood of young stars.[1]
Clear inner rings or gaps emerged in four disks, with weaker indications in three. Sz 112 contains a central cavity with a radius of 1.6 astronomical units. That scale explains why a structure invisible in earlier maps can now come into view. Two disks also carry faint outer rings beyond their bright cores. A “small disk” therefore need not mean that every trace of dust ends near its central star.[1]
Rings were familiar in large disks, while tiny disks were underrepresented in comparable surveys. Restricting the catalogue to disks whose diameters span at least three resolution elements, the team found substructure in 44% of objects measuring 3–10 astronomical units and 55% in the 10–30 range. Those rates remain below the 94–98% observed in disks wider than 30 astronomical units. Even so, a model that treats compact disks as inherently featureless now has less room: some of the earlier silence plausibly reflected the instrument’s resolving limit.[1]
The step from ring to planet
The physical importance of the rings lies in the motion of solids. Small grains can drift toward their stars through interaction with disk gas; pressure bumps can hold them at particular radii. The measured brightness patterns are compatible with such traps only a few astronomical units out. That interpretation reopens the question of how compact disks retain solids long enough for planets to grow. Assuming a planet opened each gap produces mass estimates extending toward small planets on close orbits, but those masses are model conditions rather than detections.[1]
The measurement has an equally important boundary. One wavelength cannot cleanly separate a change in actual dust density from a change hidden or reshaped by optical thickness. Features narrower than roughly two astronomical units can escape resolution. Faint outer rings also push against the shorter-baseline coverage of this ALMA configuration. Processes other than planets, especially for a central cavity, remain possible. Further maps at other wavelengths and across a wider sample of small disks can test whether this pattern persists.[1]
What has been gained is therefore not a census of planets, but access to a region the search could barely inspect before. Structures a few astronomical units from a star are now measurable; their origin remains less certain. Whether the smallest disks are truly simple is becoming an observational question.[1]