Soot Planets Instead of Water Worlds

Abstract Some low-density exoplanets are thought to be water-rich worlds that formed beyond the snow line of their protoplanetary disk, possibly accreting coequal portions of rock and water. However, the compositions of bodies within the solar system and the stability of volatile-rich solids in accretionary disks suggest that a planet rich in water should also acquire as much as 40% refractory organic carbon (“soot”). This would reduce the water mass fraction well below 50%, making the composition of these planets similar to those of solar system comets. Here we show that soot-rich planets, with or without water, can account for the low average densities of exoplanets that were previously attributed to a…

• NA
  National Aeronautics and Space Administration

  Awards: 80NSSC19K0959, 80NSSC24K0149, 80NSSC20K0259
• AP
  Alfred P. Sloan Foundation

  Award: G202114194