The planetesimal bow shock model for chondrule formation: A more quantitative assessment of the standard (fixed Jupiter) case

Abstract

Abstract-One transient heating mechanism that can potentially explain the formation of most meteoritic chondrules 1-3 Myr after CAIs is shock waves produced by planetary embryos perturbed into eccentric orbits via resonances with Jupiter following its formation. The mechanism includes both bow shocks upstream of resonant bodies and impact vapor plume shocks produced by high-velocity collisions of the embryos with small nonresonant planetesimals. Here, we investigate the efficiency of both shock processes using an improved planetesimal accretion and orbital evolution code together with previous simulations of vapor plume expansion in the nebula. Only the standard version of the model (with Jupiter assumed to have its present semimajor axis and eccentricity) is considered. After several hundred thousand years of integration time, about 4-5% of remaining embryos have eccentricities greater than about 0.33 and shock velocities at 3 AU exceeding 6 km s )1 , currently considered to be a minimum for melting submillimeter-sized silicate precursors in bow shocks. Most embryos perturbed into highly eccentric orbits are relatively large-half as large as the Moon or larger. Bodies of this size could yield chondrule-cooling rates during bow shock passage compatible with furnace experiment results. The cumulative area of the midplane that would be traversed by highly eccentric embryos and their associated bow shocks over a period of 1-2 Myr is <1% of the total area. However, future simulations that consider a radially migrating Jupiter and alternate initial distributions of the planetesimal swarm may yield higher efficiencies.

On the Origin of Banded Structure in Dusty Protoplanetary Disks: HL Tau and TW Hya

“…Each planetesimal is envisaged to be large enough such that gas drag effects are negligible, at least relative to orbital excitation through interactions with planets. This is qualitatively consistent with results from planetesimal bow shock studies (Morris et al 2012;Hood & Weidenschilling 2012).…”

Shapes of chondrules determined from the petrofabric of the CR2 chondrite NWA 801

“…; Boss and Durisen ; Desch et al. ; Morris and Desch ; Hood and Weidenschilling ; Morris et al. ; Boley et al.…”

“…Possible mechanisms responsible for melting include shockwaves (Wood 1963;Hood and Horanyi 1991;Ciesla and Hood 2002;Ciesla et al 2004;Boss and Durisen 2005;Desch et al 2005; Morris and Desch 2010;Hood and Weidenschilling 2012;Morris et al 2012;Boley et al 2013), lightning discharge (Pilipp et al 1992(Pilipp et al , 1998Desch and Cuzzi 2000), gamma-ray bursts from nearby supernovae (McBreen and Hanlon 1999;Duggan et al 2003;McBreen et al 2005), irradiation from the Sun (Shu et al 1996(Shu et al , 2001, turbulent heating by current sheets (Ryan Joung et al 2004), impact melting or volcanism , and planetesimal collisions (Asphaug et al 2011;Wakita et al 2017).…”

Planetary Embryo Bow Shocks as a Mechanism for Chondrule Formation

“…Suggested models include, e.g., winds [Shu et al, 2001], electrical shorts [McNally et al, 2013], asteroid collisions [Sanders and Scott, 2012], and nebular shocks [Morris and Desch, 2010]. Here, we explore the hypothesis that planetesimals and/or planetoids themselves are responsible for producing at least some and quite possibly the majority of chondrules [e.g., Hood, 1998, Ciesla et al, 2004, Hood and Weidenschilling, 2012. In particular, we focus on the high-temperature processing of solids in planetoidal bow shocks, building on the results of and Boley et al [2013].…”