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Why do hot Jupiters found near other stars suggest that giant planets can migrate?

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photo of Jupiter taken by Voyager 1 — Jupiter Photograph of Jupiter taken by Voyager 1 on February 1, 1979, at a range of 32.7 million km (20.3 million miles). Prominent are the planet's pastel-shaded cloud bands and Great Red Spot (lower centre).

"Hot Jupiters" are gas giants found orbiting extremely close to their parent stars, often closer than Mercury is to the Sun. Because the volatile, lighter elements required to form such massive planets can only condense in the cooler, outer regions of a solar nebula, these planets could not have formed in their current, high-temperature locations.21

Their presence near other stars suggests that giant planets are capable of significant orbital migration. Astronomers believe these planets formed in the outer reaches of their systems before migrating inward due to gravitational interactions or drag from the surrounding protoplanetary disk. This phenomenon has led scientists to reconsider the history of our own solar system, with theories like the Grand Tack hypothesis suggesting that Jupiter also underwent inward and outward migration early in its history.21