TOI-6662 b is an Earth-sized planet with a seven-hour orbit

TOI-6662 b is an Earth-sized planet orbiting a red dwarf every 7.05 hours. A search pipeline combining transit detection with follow-up checks identified the planet among 435 unresolved candidates from TESS. The results also show why light-curve classifiers alone struggle: many false alarms come from eclipses around nearby stars that mimic planetary transits.

Star system: LP 33-191 | Distance from the Sun: 69 light years

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TOI-6662 b is an Earth-sized planet with a seven-hour orbit

Star system: LP 33-191 | Distance from the Sun: 69 light years

TOI-6662 b is an Earth-sized planet that circles a red dwarf every 7.05 hours. Its measured radius is 0.94 times Earth’s, with an uncertainty of 0.03 Earth radii. The planet emerged from a search of unresolved candidates detected by TESS, a space telescope that records changes in stars’ brightness.

A computer model was trained to recognize the small, repeated dips in brightness caused by a planet passing in front of its star. A common test gave the model a high score, but that score fell to the level of random guessing when the model was tested against real false alarms rejected during TESS follow-up. The area under the receiver operating characteristic curve measures how well a classifier separates two groups; 0.5 is random performance, while 1 is perfect separation.

Many false alarms are eclipses around nearby stars. When their light mixes with the target star’s light, they can look like shallow planetary transits. A review of 145 false alarms found that 42% were such blends, placing a limit on what a classifier can achieve using brightness data from one colour band alone. A broader pipeline, CASCADE-USP, adds checks using the apparent location of the signal, high-resolution images and data from the Gaia mission. It ranks candidates and identifies what further evidence each one needs. Of 435 unresolved candidates, it selected 20; 19 were false alarms. TOI-6662 b was the remaining candidate, and its planetary classification and measured properties agreed with an independent validation.

Key findings
TOI-6662 b has a radius of 0.94 ± 0.03 Earth radii and orbits its red dwarf every 7.05 hours.
A common test gave the neural network a score of 0.97, but testing it against real rejected false alarms gave a score of 0.50.
Of 145 examined false alarms, 42% came from eclipses around neighbouring stars blended into the target’s light.
Realistic false alarms set an estimated classifier limit of 0.79; retraining reached 0.80 ± 0.06.
CASCADE-USP selected 20 candidates from 435 unresolved TESS candidates; 19 were false alarms, and TOI-6662 b was independently validated.

Scientific study

An end-to-end CNN search for ultra-short-period planets in TESS: from the blend ceiling to the independent validation of TOI-6662 b (external link)