FU Orionis outbursts, preferential recondensation of water ice, and the formation of giant planets

TL;DR

This paper explores how FU Orionis outbursts cause preferential recondensation of water ice onto specific grains in protoplanetary discs, facilitating pebble formation and potentially aiding giant planet formation.

Contribution

It quantifies the conditions under which preferential recondensation occurs and links FU Orionis outbursts to pebble creation in regions conducive to giant planet formation.

Findings

FU Orionis outbursts create conditions for rapid pebble formation.

Preferential recondensation occurs in a 4-10 au band outside the frost line.

This process may have contributed to the formation of gas giants in our Solar System.

Abstract

Ices, including water ice, prefer to recondense onto pre-existing nuclei rather than spontaneously forming grains from a cloud of vapor. Interestingly, different potential recondensation nuclei have very different propensities to actually nucleate water ice at the temperatures associated with freeze-out in protoplanetary discs. Therefore, if a region in a disc is warmed and then recooled, water vapor should not be expected to refreeze evenly onto all available grains. Instead it will preferentially recondense onto the most favorable grains. When the recooling is slow enough, only the most favorable grains will nucleate ice, allowing them to recondense thick ice mantles. We quantify the conditions for preferential recondensation to rapidly create pebble-sized grains in protoplanetary discs and show that FU Orionis type outbursts have the appropriate cooling rates to drive pebble creation in a band about 5 astronomical units wide outside of the quiescent frost line from approximately Jupiter's orbit to Saturn's (about 4 to 10 au). Those pebbles could be of the appropriate size to proceed to planetesimal formation via the Streaming Instability, or to contribute to the growth of planetesimals through pebble accretion. We suggest that this phenomenon contributed to the formation of the gas giants in our own Solar System.