The Dust Properties and Origin of Substructures in HL Tau

In 2014, one ALMA image of the dust emission in the HL Tau disk change forever our vision of how planetary systems are formed. The most intriguing characteristic was the presence of multiple bright and dark rings. Only five years ago, ALMA has discovered these structures in a large number of disks. The origin of radial substructures is still under debate, but we are sure that they are related to the formation of planetary systems. They could be the consequence of planets already formed or they could be the places where new planets will be formed. An answer to this question requires of studying the dust properties in bright and dark rings. However, we have also realized that this task is not easy even with ALMA. Bright rings seems to be associated with high density dust and they appear optically thick at ALMA wavelengths, making necessary to add observations with similar quality at longer wavelengths. Here, we present an analysis of the highest quality images available at the moment from the HL Tau disk. These images were obtained with ALMA and the VLA, and they cover a wide range of wavelengths, from 0.9 to 8 mm. The high angular resolution and sensitivity allows to separate emission from the substructures and study their dust properties. With a minimum number of assumptions, we are able to obtain dust temperature, density and maximum particle size with a physical resolution of only 7.5 au. We find that substructures at the external part of the disk (>50 au) are most probably related to the presence of a (porto)planet in an orbit of 80 au, but the internal substructures (<50 au) are more likely related to the presence of ice lines.