Narrator: Listen to part of a lecture in an astronomy class.
Professor: Now, let's talk about the discovery of exoplanets. For decades, astronomers assumed that other star systems would resemble our own, with rocky planets close to the star and gas giants farther out. But the first exoplanet found around a Sun-like star, 51 Pegasi b, in 1995, was a massive gas giant orbiting extremely close to its star—closer than Mercury is to our Sun. This was so unexpected that it challenged existing theories of planetary formation. How could such a planet form so close to its star? One idea is that these hot Jupiters actually form farther out, beyond the frost line, where ice and gas can condense, and then migrate inward over time due to gravitational interactions with the protoplanetary disk or other planets. This migration would explain why we see so many of these close-in giants. However, not all exoplanets fit this pattern. Some are on highly eccentric orbits, suggesting they were scattered by gravitational encounters. So, the diversity of exoplanets has forced us to rethink our models, and we now see that planetary systems are incredibly varied.
❓ 题目 What is the main point the professor makes about the discovery of exoplanets?
A. A. It confirmed that most star systems resemble our own solar system.
B. B. It showed that hot Jupiters are the most common type of exoplanet.
C. C. It challenged existing theories and led to a new understanding of planetary formation.
D. D. It proved that gas giants cannot form close to their stars.
✅ 正确答案
C. It challenged existing theories and led to a new understanding of planetary formation.