MCQ Detailed View

Comets are small celestial objects made mostly of frozen water, frozen gases, rock, and dust. They orbit the Sun in long, elliptical paths, spending most of their time far away in the cold outer regions of the solar system. When a comet moves closer to the Sun, the rising temperature causes significant changes in its structure.

As the Sun’s heat reaches the comet’s nucleus (its solid core), the ices begin to sublimate—changing directly from solid ice into gas without becoming liquid. This process releases gas and dust particles into space, forming a glowing cloud called the coma around the nucleus. Solar radiation and the solar wind then push this material away from the comet, creating the well-known tail, which can stretch for millions of kilometers and always points away from the Sun.

The gases released typically include water vapor, carbon dioxide, methane, and ammonia, along with fine dust grains made of silicates and organic compounds. This combination is what gives comets their visible coma and tail, making them bright and spectacular objects in the night sky.

It is incorrect to say comets release “steam,” because in space there is no atmospheric pressure for liquid water or steam to form; the ice sublimates directly into gas. The term gas and dust is scientifically accurate because these are the real components escaping from the comet.

Comets are often referred to as dirty snowballs due to their mixed composition of rock, dust, and frozen volatile materials. Studying the gases and dust emitted by comets helps astronomers learn about the early solar system, as comets are thought to contain primordial material that has remained unchanged for billions of years.

The correct answer is Gas and dust, because this is what a comet releases when it comes close to the Sun, producing its characteristic glowing tail.