GJ 15 A b is a super-Earth whose existence has been argued over. It orbits GJ 15 A, a red dwarf about 11.6 light-years away that has its own companion red dwarf, GJ 15 B. Together with its outer sibling GJ 15 A c, it makes GJ 15 A one of the closest known stars with more than one planet.
A team led by Andrew Howard announced it in 2014 from Keck Observatory's HIRES spectrograph, using the radial velocity method: a planet's gravity makes its star move slightly toward and away from us, shifting the star's light. They found a planet on an 11.44-day orbit with a minimum mass of about 5.35 Earth masses, and checked the star's brightness to rule out starspots at that period. They also found a second signal at 44 days, which they traced to the star's rotation rather than a planet.
Then the planet seemed to vanish. In 2018 a team led by T. Trifonov, using the CARMENES spectrograph and newer HIRES data, found no signal at 11.4 days and could not confirm it. Later that year a team led by M. Pinamonti combined five years of HARPS-N measurements with 15 years of Keck data, modelled the star's activity, and recovered the planet. Their signal was weaker, so they lowered its minimum mass to about 3 Earth masses. NASA has described its history as discovered, refuted, then reinstated with more data.
At that close an orbit it is hot; NASA's summary puts its surface temperature at about 530 degrees Fahrenheit, far too hot for liquid water. It has never been seen passing in front of its star, so its size and true mass are unknown. Its story is a good example of how hard it is to separate small planets from a star's own activity, and of why astronomers keep measuring.