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The Surprising Roles of Planetary Spiral Wakes

Presentation #615.15 in the session Planet Formation Theory.

Published onApr 03, 2024
The Surprising Roles of Planetary Spiral Wakes

Forming planets launch spiral wakes in the circumstellar disk they were born at. With the very first grid-based, 3D, radiative, dust-gas hydrodynamic simulations we found that they significantly contribute to the (1) vertical mixing of dust and gas in the disk, (2) help deliver dust and gas onto the planet region to be accreted, (3) contribute with ~1e-3 viscous alpha-equivalent to the angular momentum loss of the circumstellar disk, making it one of the most important angular momentum loss mechanism to date. Surprisingly, we found that even the mm-sized dust is no longer settled into the midplane, when the planet is forming and creating spiral arms in the gaseous disk. The larger the planet’s mass, the stronger is the mixing due to the vertical motions in the spiral arms. This means that the optically thin to thick transition happens above the midplane, obscuring larger dust mass from the observations. We derived the dust disk mass from ALMA mock images we created from the simulations, and compared them with the real dust mass in the simulated disk. We found 2-10x underestimation of dust mass calculated from ALMA images, meaning the real disks are significantly more massive than dust-based observations predict. This means, we have enough mass in these disks to form the observed exoplanet population, contrary to previous beliefs. The mixed up mm dust is then easily delivered to the circumplanetary region through the meridional circulation (Szulagyi+ 2014, 2022), bridging over the planetary gap and accreted from the vertical direction, flowing together with the gas. Planets do accrete vertically, as recent observations proved, and for the first time we showed via our simulations that even mm-sized pebbles are accreted from the polar direction. This vertical mixing (meridional circulation) of the spiral wakes was not considered before as an angular momentum loss mechanism. The equivalent viscous alpha that the planetary spiral wakes create is 1e-3 for a Jupiter-mass planet, making it perhaps the strongest angular momentum mechanism in the disk, after planets begin forming. Thus 3D simulations of planet formation with dust+gas are therefore vital to understand the birth of planets and the disk processes.

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