  ALMA has revolutionized our view of protoplanetary disks, revealing
structures such as gaps, rings and asymmetries that indicate dust trapping as
an important mechanism in the planet formation process. However, the high
resolution images have also shown that the optically thin assumption for
millimeter continuum emission may not be valid and the low values of the
spectral index may be related to optical depth rather than dust growth. Longer
wavelength observations are essential to properly disentangle these effects.
The high sensitivity and spatial resolution of the next-generation Very Large
Array (ngVLA) will open up the possibilities to spatially resolve disk
continuum emission at centimeter wavelengths and beyond, which allows the study
of dust growth in disks in the optically thin regime and further constrain
models of planet formation.
