Planet Formation at Cosmic Dawn: Planetesimals in H$_2$O-Rich Disks Around Low-Mass Stars
Primordial, or Pop III, supernovae (SNe) were the first, great nucleosynthetic engines in the Universe, forging the heavy elements required for the later formation of planets, and life. Past studies suggest that the rise of planet formation was gradual, and did not peak until about half of the present age of the Universe after cosmic mean metallicities exceeded a critical value. However, Pop III pair-instability (PI) SNe, which can eject over 100 M$_{\odot}$ of metals, locally enriched gas to metallicities of up to 1 Z$_{\odot}$ at Cosmic Dawn, just 100 Myr after the Big Bang. Here we show that planetesimals, the precursors of terrestrial planets, can form around low-mass, long-lived stars in the debris of such explosions, before the first galaxies and far earlier than previously thought. We modeled the collapse of a dense core with a Jeans mass of just 1 - 2 M$_{\odot}$ from a PI SN remnant and found that a protoplanetary disk formed with several Earth masses of planetesimals 0.5 - 1.0 AU from their parent star, within its water snow line. The disk has H$_2$O mass fractions that are only a factor of a few less than in the Solar System today, raising the possibility of enrichment of the first planets in the Universe with water in direct analogy to Earth in the Solar system.