Gilese 436 b is a planet that is about 30 light years away, in the constellation Leo. This planet is a hot Neptune; this means it’s a gas giant with a similar mass to Neptune. Gilese 436 b closely orbits its parent star, Gilese 436 (which is a red dwarf) in 2 days. It was discovered on 31st August 2004, by Paul Butler and Geoffrey Marcy. This was the first hot Neptune discovered with certainty.
In 2010 models of planetary atmosphere came into question, after learning more about this planet. It indicated that a hot world with a mixture of hydrogen, carbon and oxygen should have a large amount of methane and a small amount of carbon monoxide. The Spitzer Space telescope found that Gilese 436 b lack methane and had a surprising amount of carbon monoxide.
This planet is actually most well-known, for two things. One is the massive comet like tail, that follows behind the planet and is 50 times bigger than the red dwarf it orbits. We also know what it's made of, and why it’s happening. The parent star’s radiation is stripping away at the planet’s atmosphere, which creates a boiling hydrogen tail trail.
The second one is the planet, is mostly made up of ice but it’s on fire. This hot Neptune’s surface temperature is estimated to 439 °c (822 °f). Why hasn’t it melted? The planet’s gravity is so strong that all the melted liquid is frozen by pressure.
Source
https://www.nasa.gov/feature/goddard/hubble-sees-a-behemoth-bleeding-atmosphere-around-a-warm-exoplanet
https://futurism.com/the-strangest-exoplanet-ever/