Blast into 2026: Conquer the Astronomy Challenge – Your Cosmic Adventure Awaits!

The nucleus of a comet is correctly identified as the frozen center of the comet. This nucleus is primarily composed of ice, dust, and rocky material. When a comet approaches the sun, the heat causes the frozen components to sublimate, thus creating a glowing coma—a luminous cloud of gas and dust that surrounds the nucleus—and a tail that streams away from the sun due to solar wind and radiation pressure.

The nucleus is critical to understanding a comet's structure and behavior. It serves as the source for the comet's coma and tail, which are visible to observers on Earth. The composition of the nucleus is what distinguishes comets from asteroids, as they typically contain significant amounts of volatile ices like water, carbon dioxide, and ammonia.

Other choices describe aspects related to comets or other celestial bodies but do not define the nucleus itself. The luminous cloud refers to the coma, the streak of gas and dust describes the comet's tail, and the dense atmosphere of a planet does not relate to a comet's nucleus. Understanding these distinctions is essential for grasping the behavior and characteristics of comets in our solar system.