Dust dynamics modelling on the main-belt comet 324P/La Sagra

Main-belt comets (MBCs) are comet-asteroid transition objects, orbiting in the main asteroid belt. They exhibit cometary mass loss due to the sublimation of volatile ices [1]. During their active phase, MBCs eject both small and large particles. Large particles that are less affected by solar radiation pressure tend to stay closer to the nucleus of the comet and do not disperse as quickly into space as the smaller particles. The size of the large particles can inform us about the strength of the gas drag and the rate of ice sublimation. The study of ice content in MBCs allows us to constrain the distribution of volatiles in the early solar system and the formation and subsequent evolution of planetesimals.   

The presence of smaller particles complicates the measurement of larger particles due to the higher scattering cross-section of the former. One of the key observational techniques to measure the size of large particles involves analyzing the brightness profile of dust trails produced during inactive phase, when MBCs do not produce new dust and gas, allowing clearer observation of previously ejected large particles, if present.   

The MBC 324P/La Sagra has been observed to emit dust during three subsequent perihelion passages in 2010, 2015 and 2021 [2][3]. It is peculiar for developing a gap between the nucleus and the tail after the cease of its activity [4][5]. From the size of the gap, it is possible to constrain the size of the largest particles.   

Utilizing the syndyne-synchrone modeling code, we analyzed a coadded image of 324P/La Sagra that shows a faint trail on 31 December 2011, a period during which the MBC was inactive at true anomaly of 117°. The study revealed large dust particle sizes ranging from 0.2 mm to 0.8 mm over a three-month period. Further, we compared the synchrone ages with the activity profile of 324P/La Sagra to establish a temporal correlation between the particle ejection events and the historical activity phases of the MBC. 

 

References: 

[1] Hsieh, H. H. and D. Jewitt (2006) "A Population of Comets in the Main Asteroid Belt", Sci, 312, 561 

[2] Hsieh, H. H. and S. S. Sheppard (2015) "The reactivation of main-belt Comet 324P/La Sagra (P/2010 R2)", MNRAS, 454, L81 

[3] Mastropietro, M., et al. (2022) "Activity of the Main-Belt Comet 324P/La Sagra", EPSC, EPSC2022-1211 

[4] Hsieh, H. H. (2014) "The nucleus of main-belt Comet P/2010 R2 (La Sagra)", Icar, 243, 16 

[5] Snodgrass, C., et al. (2018) "The Castalia mission to Main Belt Comet 133P/Elst-Pizarro", AdSpR, 62, 1947