Post-Impact Thermal Evolution of Porous Planetesimals

TL;DR

This study models impact scenarios on planetesimals to quantify localized thermal effects, revealing that impacts can cause significant heating and melting, influencing the thermal evolution of early Solar System bodies.

Contribution

It provides the first detailed simulations of impact heating effects on porous planetesimals, highlighting their potential to cause localized melting and extended heat retention.

Findings

Impact heating can reach petrologic type 6.

Impact melting occurs at velocities > 4 km/s in porous material.

Buried impactor material insulates and prolongs heat retention.

Abstract

Impacts between planetesimals have largely been ruled out as a heat source in the early Solar System, by calculations that show them to be an inefficient heat source and unlikely to cause global heating. However, the long-term, localized thermal effects of impacts on planetesimals have never been fully quantified. Here, we simulate a range of impact scenarios between planetesimals to determine the post-impact thermal histories of the parent bodies, and hence the importance of impact heating in the thermal evolution of planetesimals. We find on a local scale that heating material to petrologic type 6 is achievable for a range of impact velocities and initial porosities, and impact melting is possible in porous material at a velocity of > 4 km/s. Burial of heated impactor material beneath the impact crater is common, insulating that material and allowing the parent body to retain the heat for extended periods (~ millions of years). Cooling rates at 773 K are typically 1 - 1000 K/Ma, matching a wide range of measurements of metallographic cooling rates from chondritic materials. While the heating presented here is localized to the impact site, multiple impacts over the lifetime of a parent body are likely to have occurred. Moreover, as most meteorite samples are on the centimeter to meter scale, the localized effects of impact heating cannot be ignored.