ELI5, Why do some extrasolar planets revolve much faster than planets here in the Solar Sytem?

Question

For example:

55 Cancri b: 0.7 days
Kepler-1649c: 19.5 days
Gliese 581g: 32 days

Compare it to Earth, which is 365 days and Mercury which is 88 days. What are the factors that cause these exoplanets revolve much faster?

In: 5

Answer 1

Simply distance from their parent star. The closer they are then the faster that they will orbit. This is why the Earth orbits the Sun at 30kps but Neptune orbits at only about 5kps.

If they were orbiting slower then they would fall into a closer orbit if not into the Sun itself.

It’s unlikely that most of the exoplanets that we’ve discovered so close to their parent formed there since most of them are most likely gas giants which form further out. So what has most likely happened is that some sort of event has caused them to migrate closer to their parent star and therefore a faster orbit.

Now, there is a bit of some sort of selection bias here because we’re much more likely to discover an exoplanet that orbits closer to its parent star because their closer orbits makes them easier to detect.