Q0957+561 A,B is a quasar, one component of which (A) was seen to undergo a change in brightness possibly as a result of microlensing by a planet-sized body located in a foreground galaxy.¹ If the lensing object, estimated to have a mass about 0.01 times that of Jupiter, exists, then it may be a rogue planet since no lensing effect was observed that could be attributed to a host star. However, this interpretation would imply that there are about one million rogue planets per star, a number far greater than that predicted by our present understanding of planet formation. On the other hand, it has been suggested that the light curve variations could have been caused by a drop in the quasar's energy flux.²

 

References

1. Schild, R. E. "Microlensing Variability of the Gravitationally Lensed Quasar Q0957+561 A,B," Astrophysical Journal, 464, 125 (1996).
2. Kundic, T., et al. "An Event in the Light Curve of 0957 +561A and Prediction of the 1996 Image B Light Curve," Astrophysical Journal Letters, 455, L5 (1996)