Final answer:
The correct description for a comet is that it is a leftover planetesimal from the outer region of the frost line. It's primarily composed of ice and dust and forms a head and tail of gas when near the Sun. B) It is a leftover planetesimal formed in the outer region of the frost line.
Step-by-step explanation:
The statement that best describes a comet is B) It is a leftover planetesimal formed in the outer region of the frost line. A comet consists mostly of icy components such as water, carbon dioxide, and carbon monoxide. As comets orbit the Sun, particularly those from the distant Oort cloud or the closer Kuiper belt, they form a tenuous gas head and often display a spectacular tail when near the Sun due to sublimation of their icy parts.
Comets are renowned for their impressive appearance as they approach the Sun, which causes them to develop an atmosphere, and occasionally two visible tails: the dust tail and the ion tail. The nucleus of a comet is a solid chunk of ice and dust. Comets are fundamentally different from asteroids, which are mainly rocky or metallic and reside in regions like the asteroid belt between Mars and Jupiter. Asteroids exhibit little of the volatile behavior seen in comets. Comets are typically described as small, icy bodies that originate from the outer regions of the solar system. They are believed to be leftover planetesimals, which are small, primitive bodies that never coalesced into planets during the early formation of the solar system. The outer region where comets are thought to form is beyond the frost line, where volatile compounds like water ice can condense. As comets approach the Sun, they develop a glowing coma and tail due to the sublimation of ices and the interaction with solar radiation. Option B accurately captures the nature and origin of comets.