HD 209458 b (Osiris), discovered in 1999, is a puffy Hot Jupiter ~1.4 times Jupiter’s size orbiting a Sun-like star every 3.5 days. First with detected atmosphere—boiling off hydrogen into a comet tail.
Inflated and evaporating, dayside ~2,000°F (1,100°C)—no life, just cosmic leak.
The “evaporating planet” that proved we can study alien air from Earth.