unlike for bodies within our solar system, there is no clearly established method for officially recognizing an exoplanet. according to the international astronomical union, an exoplanet should be considered confirmed if it has not been disputed for five years after its discovery. there have been examples where the existence of exoplanets has been proposed, but even after follow-up studies their existence is still considered doubtful by some astronomers. such cases include: alpha centauri (4.36 ly, two in 2012 and 2013), lalande 21185 (8.31 ly, in 2017), groombridge 34 (11.7 ly, two in 2014 and 2017), lhs 288 (15.6 ly, in 2007), 40 eridani (16.3 ly, in 2018), and gliese 682 (16.6 ly, two in 2014). there are also some instances where proposed exoplanets were later disproved by subsequent studies, such as candidates around teegarden's star (12.6 ly), van maanen 2 (13.9 ly), groombridge 1618 (15.9 ly), and vb 10 (18.7 ly).