托福听力

🎧 听力原文

Narrator: Listen to part of a lecture in an astronomy class. Professor: Now, when we talk about the search for exoplanets, one of the most exciting discoveries is the 'hot Jupiter'—a gas giant that orbits very close to its star. You might think these planets are rare, but they've taught us a lot about planetary migration. Initially, astronomers assumed that gas giants form far from their star, where ice and gas are abundant. But hot Jupiters are found extremely close in, sometimes with orbital periods of just a few days. So how did they get there? The leading theory is that they migrated inward due to gravitational interactions with the protoplanetary disk—the swirling gas and dust around a young star. This disk can exert drag, causing the planet to spiral inward. However, this migration must happen early, before the disk dissipates, which typically occurs within a few million years. Some models also suggest that gravitational tugs from companion planets or even another star can fling a hot Jupiter into a closer orbit later. But the disk migration theory is favored because it explains why many hot Jupiters have nearly circular orbits. So, in essence, these planets provide a window into the dynamic processes of early solar system formation.