Which description best fits the Helix Nebula?

The Helix Nebula is best described as a planetary nebula. This classification is based on its formation; it originated from the outer layers of a star that has reached the end of its life cycle, typically a star similar to our Sun. As the star exhausts its nuclear fuel, it expels its outer layers into space, creating a glowing shell of ionized gas.

Planetary nebulae, including the Helix Nebula, are characterized by their doughnut or ring-like appearance, the result of the way the ejected material moves away from the dying star and the different velocities at which layers of gas are expanding. Additionally, the central star left behind after the ejection of these layers is usually a hot white dwarf, which illuminates the surrounding gas, contributing to the nebula's brightness.

In contrast, emission nebulae are regions where gas is ionized by nearby hot stars, dark nebulae are dense clouds of gas and dust that block light from objects behind them, and supernova remnants are the remains of massive stars that have exploded in supernova events. The specific characteristics of the Helix Nebula align closely with those of planetary nebulae, making this classification the most accurate.