Tracking water ice from small dust to the first planetesimals

The water snowline is thought to play a key role in the formation of the first planetesimals. Planetesimal formation requires efficient local concentration of large pebbles, a condition that is difficult to achieve throughout protoplanetary disks. Near the snowline, icy grains are expected to stick more efficiently than silicate grains as they approach their sublimation temperature. In addition, water vapor from the hotter inner disk can diffuse outward, recondense onto solids in colder regions, and thereby enhance the local solid-to-gas ratio. Together, these processes make the snowline a particularly favorable site for planetesimal formation. Whether iron meteorites, which likely formed within the first Myr of the solar system formation, originated near the snowline remains an open question [1-3].

While planetesimal formation at the water snowline has been extensively studied, most previous models assume a single dust size and composition at each radial location and neglect the vertical structure of the disk. In reality, dust particles grow and fragment into a distribution of sizes that evolve differently in both the radial and vertical directions, an aspect that has been shown to impact late-stage planetesimal formation beyond the water snowline, in regions linked to the formation of chondritic meteorites [4]. Small grains are also known to acquire proportionally more water ice than larger grains, potentially affecting the water enrichment near the snowline [5].

In this talk, we present a new Monte Carlo model to investigate the coupled evolution of dust composed of ice and silicate in young two-dimensional disks [6]. Our model includes dust coagulation and fragmentation, ice evaporation and condensation on grains of different sizes, and the radial and vertical transport of both solids and water vapor. This approach enables us to constrain the ice-to-rock ratios of planetesimals forming at the water snowline and to trace the evolutionary history of water ice before its incorporation into planetesimals. The predicted composition and formation timescales of these planetesimals will be compared to those observed among meteorites, and thus could eventually constrain whether some iron meteorite parent bodies formed near the water snowline.

 

References:

[1] J. Drazkowska and Y. Alibert, 2017, Astronomy & Astrophysics, 608, A92
[2] T. Lichtenberg, J. Drazkowska, M. Schönbächler, et al., 2021, Science, 371, 6527
[3] A. Morbidelli, K. Baillié, K. Batygin, et al., 2022, Nature Astronomy, 6, pages 72–79
[4] N. Gurrutxaga, J. Drazkowska, V. Vaikundaraman, T. Kleine, 2026, The Astrophysical Journal, in press
[5] S. Krijt, F. Ciesla, A. Bergin, 2016, The Astrophysical Journal, 833, 2
[6] N. Gurrutxaga, V. Vaikundaraman, J. Drazkowska, 2026, Astronomy & Astrophysics, 709, A164