  Transiting super-Earths orbiting bright stars in short orbital periods are
interesting targets for the study of planetary atmospheres. While selecting
super-Earths suitable for further characterization from the ground among a list
of confirmed and validated exoplanets detected by K2, we found some suspicious
cases that led to us re-assessing the nature of the detected transiting signal.
We did a photometric analysis of the K2 light curves and centroid motions of
the photometric barycenters. Our study shows that the validated planets K2-78b,
K2-82b, and K2-92b are actually not planets but background eclipsing binaries.
The eclipsing binaries are inside the Kepler photometric aperture, but outside
the ground-based high resolution images used for validation. We advise extreme
care on the validation of candidate planets discovered by space missions. It is
important that all the assumptions in the validation process are carefully
checked. An independent confirmation is mandatory in order to avoid wasting
valuable resources on further characterization of non-existent targets.
