GPS Event Calendar

"Race to the center of the disk: how dust dynamics leads to preferential formation of gas giants at intermediate distances and the co-existence of cold giants and hot super-Earths"

Yayaati Chachan, Graduate Student, Planetary Science, California Institute of Technology

Abstract: Multiple observational studies suggest that giant planet occurrence peaks at a few au and declines both closer-in and further-out from their host stars. This occurrence pattern is commonly attributed only to the presence of larger cores at such separations. Here, we argue that location-dependent gas accretion also plays an important role in enhancing giant planet occurrence at intermediate distances. Differences in fragmentation velocity thresholds for icy and ice-free grains lead to a non-monotonic dust-to-gas ratio as a function of location in the disk. The accretion of dust poor gas from high above the disk midplane in dust-depleted regions of the disk at ~1-10 au rapidly leads large planetary cores to the threshold for runaway gas accretion, thus creating giant planets and boosting their occurrence rate. Location dependent gas accretion rates might also explain why most super-Earths only acquire envelopes that are a few % by mass while ‘super-puffs' acquire envelopes that are 10s of % by mass, despite having similar core masses. We also show that even though giant planet cores eventually grow massive enough to stop the flow of solids from the outer to the inner disk, they usually let enough solids through to the inner disk by this time for super-Earths to form. Large and massive disks that are conducive for cold giant planet formation tend to provide favorable conditions for inner super-Earth formation too, thus explaining why they often co-exist in nature. Finally, we show that super-Earth progenitors must already be more massive than Mars by the time the giant planet core stems the flow of solids to the inner disk.

"TBD"

Jiaxuan Li, Caltech