ASTRONOMY FUNDAMENTALS - Chapter 6, Exercise 3 Solution
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Distinguishing a Comet from an Asteroid by Behavior

PROBLEM
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Two small solar-system bodies pass close to the Sun. Object A develops
a visible tail; Object B does not. Explain which is more likely a comet
and which is more likely an asteroid, and why.

SOLUTION
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Object A (develops a visible tail) is more likely a COMET.
Object B (does not develop a tail) is more likely an ASTEROID.

The chapter's own real, key distinguishing feature between the two is
compositional: comets contain volatile material - ices such as water,
carbon dioxide, and others - mixed into their nucleus. As a comet
approaches the Sun, solar heating causes those volatiles to sublimate
(turn directly from solid to gas), releasing gas and dust that forms
the real, characteristic tail streaming away from the nucleus.

Asteroids, by contrast, are rockier bodies that formed inside Jupiter's
own orbit, closer to the Sun, where it was too warm for large amounts
of volatile ice to have accumulated in the first place. Without that
volatile material to sublimate, an asteroid passing near the Sun simply
heats up without producing the gas-and-dust tail a comet's own icy
composition makes possible.

ANSWER: Object A, with its visible tail, is more likely a comet, since
tail formation is driven by sublimating volatile ices unique to comets.
Object B, lacking a tail despite passing close to the Sun, is more
likely an asteroid, since asteroids are rockier and lack the volatile
material needed to produce a tail.

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WHY THIS WORKS AS AN ANSWER

The presence or absence of a tail is a genuinely reliable, observable
real behavioral clue precisely because it traces back to a real,
underlying compositional difference established when these two kinds
of bodies actually formed - comets farther out in the volatile-rich
outer Solar System (the Kuiper Belt and Oort Cloud), asteroids closer
in, within the warmer region inside Jupiter's own orbit. This is
exactly the kind of real physical reasoning - inferring composition
and origin from directly observable behavior - that underlies much of
how astronomers classify small solar-system bodies in actual practice.