One of the most perplexing issues raised by the discovery of thousands of exoplanets is the existence of "hot Jupiters" - planets with the masses and compositions of Jupiter, but orbiting closer to their stars than Mercury does in our solar system. What is our best idea currently about how such "hot Jupiters" came to be?
A) each hot Jupiter came directly out of the star it now orbits and must be made of the exact same material at only slightly lower temperatures
B) hot Jupiters formed by the collision and merger of many terrestrial planets - these collisions heated them up
C) hot Jupiters formed in an asteroid belt and are made of countless asteroids that are hot
D) hot Jupiters formed further out in their star system, and then migrated inward somehow
E) hot Jupiters are artificial; they were made by super-advanced alien beings to make the universe more interesting
Section 14.5: Planetary Evolution

Question

Quizplus · Accepted Answer

The most widely accepted theory for the formation of hot Jupiters is that they formed further out in their star system, beyond the "snow line" where it was cool enough for water and other volatile substances to freeze into solid particles. This allowed the planets to grow larger and more massive, until their gravity was strong enough to pull in surrounding gas and form a gas giant. However, something caused these planets to migrate inward towards their star, perhaps due to interactions with other planets in the system, or through gravitational interaction with their star's disk of gas and dust. This migration could have caused the planets to reach their current, much closer orbits.

One of the Most Perplexing Issues Raised by the Discovery