Comets are described as

Comets are described as

• A. A planet with rings
• B. An asteroid with a tail
• C. A disk-shaped object of ice and dust
• D. A celestial object consisting of a nucleus of ice and dust and, when near the sun, a tail of gas and dust particles pointing away from the sun

Answer: (D)

Comets are icy bodies that carry dust and small particles, and they reveal tails when heated by the Sun. The defining feature is a solid nucleus made of ice and dust. As the comet travels closer to the Sun, the heat causes the ices to sublimate into gas and pick up dust, creating a surrounding coma and, with solar radiation and the solar wind, tails that extend away from the Sun. This tail always points away because the Sun’s influence pushes gas and dust outward. The description that matches this behavior—an object with a nucleus of ice and dust that, near the Sun, develops a tail of gas and dust pointing away from the Sun—captures both the composition and the Sun-driven tail phenomenon. The other descriptions miss this combination of a solid icy nucleus and Sun-facing activity that produces a tail.

Comets are icy bodies that carry dust and small particles, and they reveal tails when heated by the Sun. The defining feature is a solid nucleus made of ice and dust. As the comet travels closer to the Sun, the heat causes the ices to sublimate into gas and pick up dust, creating a surrounding coma and, with solar radiation and the solar wind, tails that extend away from the Sun. This tail always points away because the Sun’s influence pushes gas and dust outward. The description that matches this behavior—an object with a nucleus of ice and dust that, near the Sun, develops a tail of gas and dust pointing away from the Sun—captures both the composition and the Sun-driven tail phenomenon. The other descriptions miss this combination of a solid icy nucleus and Sun-facing activity that produces a tail.