Rings in a Young Embedded Disk: Footholds of Planet Formation at Early Times

<p>Ringed protoplanetary disks, in the Class II phase of low-mass star formation when the envelope has mostly dispersed, have been found in abundance in recent years with high-resolution ALMA observations. These ringed disks have been often interpreted as evidence of ongoing planet formation. In the younger Class 0 and I phases there are few examples of high resolution dust disk observations due to the challenge of the dense envelope surrounding the disk, and more often than not reveal spiral-like structures. However, these embedded stages may be when the first steps of planet formation occur, and studying ringed structures in these phases will constrain the initial conditions of planet formation. We have used ALMA 1.3 mm long-baseline dust continuum observations to study the Class I protostar IRS 63 with 7 au resolution and expose the detailed physical structure of a Class I disk. The ALMA data indicate that concentric dust rings are present in the disk, revealing IRS 63 is the youngest-known protostellar disk with multiple ringed dust substructures and demonstrating that these features are already present in the Class I phase. The dust ring structures could arise via several mechanisms including rapid pebble growth near snowlines, magnetorotational instabilities, asymmetric accretion from the envelope to disk, or planet-disk interactions carving gaps in the disk. Even if planets have not yet formed, dust rings in disks at such an early evolutionary stage could provide a stable environment for long enough time scales to grow planets.</p>