The Gaia space telescope measures star positions with an accuracy of a microarcsecond, like spotting a coin on the Moon from Earth. In 2022, it noticed that the bright star HD 12800 was wobbling slightly, as if tugged by an invisible companion. Astronomers hypothesized that a planet orbits the star.
But a wobble can be deceiving. Stars themselves tremble from internal processes, and instruments sometimes err. To test the idea, a team of scientists pointed the TRES spectrograph at the star. This instrument catches shifts in starlight: if a planet exists, the star alternately approaches and recedes, and its spectral lines wander back and forth. Observations spanned two years, and no trace of a planet was found.
This case is not a failure but a lesson. Gaia will soon release a new catalog with thousands of planet candidates. Many stars will be too faint for precise checks, but for moderately bright stars (like HD 12800), ordinary spectrographs such as TRES will serve as a reliable filter. That way, false alarms get weeded out, and real planets get confirmed.
The Gaia telescope is so sensitive that it could notice a person on the Moon waving their hand — if a person were there.
In Stanisław Lem's novel Solaris, scientists also struggled for a long time to determine whether the planet had moons, until they encountered a living ocean.