  Planetesimals are born fragile and are subject to destruction by wind erosion
as they move through the gas of a protoplanetary disk. In microgravity
experiments, we determined the shear stress necessary for erosion of a surface
consisting of 1 mm dust pebbles down to 1 Pa ambient pressure. This is directly
applicable to protoplanetary disks. Even pebble pile planetesimals with low
eccentricities of 0.1 cannot survive inside of 1 au in a minimum-mass solar
nebula, and safe zones for planetesimals with higher eccentricities are located
even farther out.
