Comet C/2021 S3 (PANSTARRS) is a long-period comet that was discovered by the Pan-STARRS survey on September 27, 2021. The comet's highly elliptical orbit takes it from the distant reaches of the solar system into the inner solar system, where it becomes visible from Earth. As it approaches the Sun, the comet's icy nucleus heats up, causing it to shed gas and dust and form a glowing coma and often a tail that points away from the Sun.

One of the notable features of C/2021 S3 (PANSTARRS) is its brightness, which has allowed for detailed observations and photography by both professional and amateur astronomers. The comet's composition provides insights into the early solar system, as it is made up of primordial materials that have remained largely unchanged since the solar system's formation. Observations of the comet's behavior and its interactions with solar radiation help scientists understand the physical and chemical processes that occur in these distant celestial visitors.