Astrophysics Colloquium Observing Planet Formation with the VLA in the Era of ALMA Presented by Carlos Carrasco-Gonzalez Universidad Nacional Autónoma de México, Centro de Radioastronomia y Astrofisica Thursday, January 18, 2018 11:00 A.M. in 169-336 and on Webex Abstract The first long-baseline ALMA campaign resolved the disk around the young star HL Tau into a number of axisymmetric bright and dark rings. Despite the very young age of HL Tau, these structures have been interpreted as signatures for the presence of (proto)planets. The ALMA images triggered numerous theoretical studies based on disk-planet interactions, magnetically driven disk structures, and grain evolution. Of special interest are the inner parts of disks, where terrestrial planets are expected to form. However, the emission from these regions in HL Tau turned out to be optically thick at all ALMA wavelengths, preventing the derivation of surface density profiles and grain-size distributions. Here, we present the most sensitive images of HL Tau obtained to date with the VLA at 7.0 mm wavelength with a spatial resolution comparable to the ALMA images. At this long wavelength, the dust emission from HL Tau is optically thin, allowing a comprehensive study of the inner disk. Our optically thin data also suggest high density, fast grain growth, fragmentation, and formation of dense clumps in the inner densest parts of the disk. Our results suggest that the HL Tau disk may be actually in a very early stage of planetary formation, with planets not already formed in the gaps but in the process of future formation in the bright dense rings. JPL Contact: Mario Flock (4-7361)   Site Manager: Webmaster: CL 08-3220