EVSN - On Background - Comets, the Basics

Comets aren't just icy visitors from the outer solar system—they're time capsules of the early solar system's formation, carrying frozen volatiles and primordial dust. Dr. Pamela Gay explains that comets originate from two major reservoirs: the Kuiper Belt beyond Neptune and the distant Oort Cloud, both shaped by gravitational interactions over billions of years. What makes comets so visually dramatic is not their small solid nuclei—typically just a few kilometers across—but the vast, dynamic atmospheres they develop when heated by the Sun. As ice sublimates directly into gas, it creates a glowing coma and two distinct tails: an ion tail pushed straight away from the Sun by solar radiation, and a dust tail that curves due to orbital momentum. These tails can ripple and even be severed by solar storms, as seen in Comet C2025A6 Lemon during solar maximum. The episode also reveals that interstellar comets like 3i Atlas pass through our system regularly—possibly 6 to 12 per year—undetected, reminding us that our solar system is constantly exchanging material with the galaxy. This foundational episode sets the stage for future deep dives into comet discovery, citizen science, and the profound impact comets have had on Earth’s history, from ancient meteor storms to modern astrophysical insights.