The TESS telescope, like a patient sentinel, stares at the same stars for months, waiting for a planet to momentarily block its star's light. But the sentinel has blind spots: some dim red dwarfs only came into its field of view for a short time, so their planets could have gone unnoticed. Now astronomers have selected 121 such stars that have only recently accumulated enough observations and given them their first thorough check.

Each star is like a lamp that sometimes has something passing in front of the bulb, slightly dimming the light. The scientists looked for such flickers with periods from half a day to a hundred days. To do this, they ran the data through several filters: first an automated signal search, then a check for interference from neighboring stars, and finally a comparison with data from the Gaia space telescope, which knows the exact position of every star. Out of hundreds of thousands of red dwarfs, they selected 121, and among them they found 20 suspicious flickers in 16 systems.

The remaining signals are weaker for now: they could be noise, but they could also be confirmed if TESS looks at these stars a few more times. One star showed a single flicker — possibly a planet with a very long year passed in front of it just once during the entire observation period.

Now astronomers have a list of addresses where to point more powerful telescopes. Every confirmed planet around such a dim star is a chance to find a world like Earth: red dwarfs live for hundreds of billions of years, and their planets have had plenty of time to become habitable.