AI Summary

Ultra‑short‑period (USP) exoplanets orbit their stars in less than 24 hours, making them the fastest known planets. They are found by missions such as Kepler and TESS. Because they lie so close to their host stars, USPs receive intense stellar radiation that can strip away any atmospheres they once had. Ancient astronomers named Mercury after the swift messenger god, but even Mercury’s 88‑day orbit is slow compared to these rapidly rotating worlds. The loss of atmospheres is a key consequence of the extreme conditions these planets endure.

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