Overcoming the Meter Barrier and The Formation of Systems with   Tightly-packed Inner Planets (STIPs)
  We present a solution to the long outstanding meter barrier problem in planet formation theory. As solids spiral inward due to aerodynamic drag, they will enter disk regions that are characterized by high temperatures, densities, and pressures. High partial pressures of rock vapor can suppress solid evaporation, and promote collisions between partially molten solids, allowing rapid growth. This process should be ubiquitous in planet-forming disks, which may be evidenced by the abundant class of Systems with Tightly-packed Inner Planets (STIPs) discovered by the NASA Kepler mission. 
Aaron C. Boley, Melissa A. Morris, and Eric B. Ford
astro-ph.EP