You're likely thinking of Gliese 581g, a planet that was discovered in 2010 orbiting the red dwarf star Gliese 581. While it was initially considered a strong candidate for a potentially habitable exoplanet, its existence has been debated.

Here's what we know about it:

* Location: It orbits Gliese 581, a red dwarf star located about 20 light-years from Earth in the constellation Libra.

* Size: Gliese 581g is thought to be about twice the size of Earth and has a mass around 3-4 times that of our planet.

* Orbit: It orbits its star in a tight circle, completing a revolution in just 37 Earth days.

* Potential Habitability: Gliese 581g is located within the habitable zone, the region around a star where liquid water could potentially exist on the surface of a planet. This made it a very exciting discovery.

* Challenges: However, the planet's close proximity to its star means it is likely tidally locked, with one side always facing the star. This could result in extreme temperature differences between the two sides, making it difficult for life to thrive.

* Controversy: The original discovery paper, published in 2010, was later challenged by other researchers. The lack of confirmation from other telescopes and the uncertainty of the planet's signal led to much debate about its actual existence.

* Current Status: As of today, Gliese 581g is not widely considered to be a confirmed exoplanet. Further observations and research are needed to determine if it truly exists.

While the existence of Gliese 581g remains uncertain, it's still an important discovery. It sparked an intense debate about the criteria for considering a planet habitable, and it fueled the search for other potentially habitable worlds beyond our solar system.