Fates of hydrous materials during planetesimal collisions

Abstract

Hydrous minerals are found on the surfaces of asteroids, but their origin is not clear. If their origin is endogenic, the hydrous minerals that were formed in the inner part of a planetesimal (or parent body) should come out on to the surface without dehydration. If their origin is exogenic, the source of hydrous minerals accreting onto asteroids is needed. Collisions in the asteroid belt would be related to both origins because collisions excavate the surface and eject the materials. However, the fate of hydrous minerals in large planetesimals during the collisional process has not been well investigated. Here, we explore planetesimal collisions by using the iSALE-2D code, and investigate the effect of an impact for the target planetesimal containing hydrous minerals. Our numerical results for the fiducial case (5 km/s of the impact velocity) show that hydrous minerals are slightly heated during the collisions. This moderate heating indicates that they can avoid the dehydration reaction and keep their original composition. Some hydrous minerals have larger velocity than the escape velocity of the collision system. This means that hydrous minerals can escape from the planetesimal and support the theory of exogenic origin for the hydrous minerals on asteroids. Meanwhile, the velocity of other hydrous minerals is smaller than the escape velocity of the system. This also indicates the possibility of an endogenic origin for the hydrous minerals on asteroids. Our results suggest that hydrous minerals on asteroids can be provided by planetesimal collisions.

Enhancement of Impact Heating in Pressure‐Strengthened Rocks in Oblique Impacts

“…Figure 4 shows the distribution of T peak and P peak . The peak temperature are systematically higher than the temperatures on the Hugoniot curve (dash-dotted lines) as discussed in previous works Wakita & Genda, 2019). The relationship between T peak and P peak differs in both impact cases.…”

“…Melosh and Ivanov (2018) emphasized that the role of material strength in rocky materials have been overlooked for a long time. This additional heating could cause dehydration in chondrite parent bodies (Wakita & Genda, 2019). The shock stages of meteorites typically grouped by their thermal properties (e.g., Stöffler et al, 1991) may need to be reevaluated.…”

“…The shock stages of meteorites typically grouped by their thermal properties (e.g., Stöffler et al, 1991) may need to be reevaluated. This additional heating could cause dehydration in chondrite parent bodies (Wakita & Genda, 2019). However, these pioneering studies only performed numerical calculations of head-on impacts with a two-dimensional shock physics code.…”

Distant Formation and Differentiation of Outer Main Belt Asteroids and Carbonaceous Chondrite Parent Bodies

“…Moreover, non‐disruptive impacts through the Solar System history influenced asteroid surface compositions by removing and excavating endogenous materials and replenishing impactor materials. Decomposition of hydrous minerals due to impacts is expected to be limited (Wakita & Genda, 2019). Cumulative impacts have affected Ceres surface composition, though endogenous NH 4 ‐bearing phyllosilicates still remain (Marchi et al., 2019; Stein et al., 2019).…”

Distant formation and differentiation of outer main belt asteroids and carbonaceous chondrite parent bodies

“…Moreover, non-disruptive impacts through the Solar System history influenced asteroid surface compositions by removing and excavating endogenous materials and replenishing impactor materials. Decomposition of hydrous minerals due to impacts is expected to be limited (Wakita & Genda, 2019). Cumulative impacts have affected Ceres surface composition, though endogenous NH 4 -bearing phyllosilicates still remain (Stein et al, 2019;Marchi et al, 2019).…”