Three TESS dips in TIC 218977148 fit a 31.94008-day period if one stable source gives one dip per cycle and P >= 20 days

TIC 218977148 was reported as a planet candidate with two TESS dips. We search later public data and measure a third dip in sector 96. Its center is BTJD 3910.67359, its fitted depth is 5.58 parts per thousand, and its total duration is 6.94 hours. We fit all three event times and test integer cycle counts for periods of at least 20 days. The best cycle counts are 0, 23, and 80. They give a period of 31.9400823 days and chi-square 1.920 for one degree of freedom. The formal period error is 0.0000729 days under the stated noise model. This result assumes one stable source and one dip per cycle. The nearest other prediction from the first two times misses the third event by 31.44 hours. Raw aperture flux also contains the third dip. The source image and lost-light image peak on the same pixel. A nearby star on the same detector has no matching dip. A distant comparison star has a narrower dip near the same time, so a common instrument effect remains possible. The physical cause is open, and this study does not confirm a planet. We preserve the source data, pixel subset, provenance, fit draws, figures, timing grid, and code. The time model gives specific dates for new tests.

TESS · TIC 218977148 · transit timing · duotransit candidates · public astronomical data · period aliases · reproducible research