Final answer:
Planetary migration explains the presence of close-in exoplanets through tidal forces and gravitational interactions.
Step-by-step explanation:
The concept of planetary migration helps explain the presence of close-in exoplanets through tidal forces and gravitational interactions. When a planet interacts with the remnant material in the circumstellar disk, it can experience a headwind or friction that causes it to lose energy and spiral inward. Some migrating planets can stop their inward motions and escape destruction, resulting in the presence of close-in exoplanets.