Effect of Dust Rotational Disruption by Radiative Torques and Implications for the F-corona Decrease Revealed by the Parker Solar Probe

The first-year results from the Parker Solar Probe (PSP) reveal a gradual decrease of F-coronal dust from distances of D = 0.166–0.336 au (or the inner elongations of ∼9.22–18.69 R ⊙ ) to the Sun. Such an F-corona decrease cannot be explained by the dust sublimation scenario of the popular silicate composition that implies a dust-free boundary zone at heliocentric radius R ≲ 4–5 R ⊙ , but it may be explained by appealing to various dust compositions with different sublimation fronts. In this paper, we present an additional explanation for the F-corona decrease using our newly introduced mechanism of dust destruction, the so-called Radiative Torque Disruption (RATD) mechanism. We demonstrate that the RATD rapidly breaks large grains into nanoparticles so that they can be efficiently destroyed by nonthermal sputtering induced by the bombardment of energetic protons from slow solar winds, which extends the dust-free zone established by thermal sublimation to R dfz ∼ 8 R ⊙ . Beyond this extended dust-free zone, we find that the dust mass decreases gradually from R ∼ 42 R ⊙ toward the Sun due to partial removal of nanodust by nonthermal sputtering. The joint effect of the RATD and nonthermal sputtering can successfully reproduce the gradual decrease of the F-corona between 19 and 9 R ⊙ observed by the PSP. Finally, the RATD mechanism can efficiently produce nanoparticles usually observed in the inner solar system.