A faint outer ring enlarges Sz 76’s planet-forming disk
New observations of the young star Sz 76 reveal a faint dust ring beyond its bright compact disk. An observational preprint places the ring at roughly 45 Earth–Sun distances. Including that extended emission substantially enlarges the inferred dust radius and changes the gas-to-dust size ratio, weakening a previous interpretation based on strong inward drift.
Science··Morning
The outer ring lies about 45 Earth–Sun distances away
A faint ring surrounds the compact, brightly emitting disk around Sz 76, a young star in the Lupus star-forming region. Giulia Ricciardi and colleagues describe new observations with the ALMA radio telescope array in an observational preprint submitted on 7 October. The ring lies at roughly 45 astronomical units; one such unit is the average Earth–Sun distance. A model containing both a central component and a ring fits the measurements better than a central component alone.[1]
Including the ring changes the gas-to-dust size ratio
With the ring included, 68 per cent of dust emission falls within a radius of about 41 astronomical units; the previous estimate was roughly 7 astronomical units. Gas traced through carbon-monoxide emission extends to roughly 77 astronomical units. The inferred gas-to-dust size ratio becomes about 2 rather than 11. This revised spatial distribution weakens the basis for an interpretation involving strong, unimpeded inward drift of dust. Grain speeds were not directly tracked.[1]
Earlier observations resolved an inner depletion but lacked sufficiently short antenna separations to recover some faint extended emission. Lower-resolution measurements had also hinted at outer light. The new analysis separates this component as a ring. The authors discuss dust trapped in a pressure maximum and explore a planet–disk interaction model. A proposed companion remains an interpretation of the structure, with the result confined to this one young-star system.[1]
