TOI-2431 b is an ultra-hot mini-Neptune discovered in 2019 by NASA’s TESS mission and confirmed in 2025. It’s about 3.5–4.0 times Earth’s size with a thick, puffy atmosphere, orbiting a K-type star every 5.4 hours—its “year” is shorter than a single day on Earth!
Dayside temperatures soar to ~2,063 K (~3,350°F), turning it into a scorching roaster with no chance for liquid water or life. The star is relatively young and quiet, but the extreme proximity means the planet is likely losing atmosphere fast.
This hot mini-Neptune shows how planets can puff up from intense heat, making it a prime target for studying atmospheric escape.