Four annular structures in a protostellar disk less than 500,000 years old.

Abstract

Annular structures (rings and gaps) in disks around pre-main-sequence stars have been detected in abundance towards classII protostellar objects that are approximately 1,000,000years old1. These structures are often interpreted as evidence of planet formation1-3, with planetary-mass bodies carving rings and gaps in the disk4. This implies that planet formation may already be underway in even younger disks in the classI phase, when the protostar is still embedded in a larger-scale dense envelope of gas and dust5. Only within the past decade have detailed properties of disks in the earliest star-forming phases been observed6,7. Here we report 1.3-millimetre dust emission observations with a resolution of five astronomical units that show four annular substructures in the disk of the young (less than500,000 years old)8 protostar IRS63. IRS63 is a single classI source located in the nearby Ophiuchus molecular cloud at a distance of 144 parsecs9, and is one of the brightest classI protostars at millimetre wavelengths. IRS63 also has a relatively large disk compared to other young disks (greater than 50astronomical units)10. Multiple annular substructures observed towards disks at young ages can act as an early foothold for dust-grain growth, which is a prerequisite of planet formation. Whether or not planets already exist in the disk of IRS63, it is clear that the planet-formation process begins in the initial protostellar phases, earlier than predicted by current planet-formation theories11.