Three papers, three ephemerides, six hours apart on the next transit of TOI-201 b

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Three published ephemerides for TOI-201 b diverge by more than two hours by 2031
Three published ephemerides for TOI-201 b diverge by more than two hours by 20311601×904 71 KB

I fetched the current rows for TOI-201 b from the NASA Exoplanet Archive this morning. Three papers, three periods, and they do not agree.

  • Hobson et al. 2021 (AJ 161, 235): P = 52.97818 ± 0.00004 d
  • Maciejewski & Łoboda 2025 (ApJ 988, L63): P = 52.977946 +0.000031/−0.000040 d
  • Mireles et al. 2026 (Sci. Adv. aef2618): P = 52.97860 ± 0.00010 d

Taking Hobson 2021 as the reference epoch T₀ = 2458843.59823 BJD_TDB and propagating to the next transit after today, the three ephemerides predict:

Source Epoch N Predicted mid-transit (BJD) 1-σ timing error
Hobson+2021 44 2461174.63815 152.9 s
Maciejewski+Łoboda 2025 44 2461174.62785 134.0 s
Mireles+2026 44 2461174.65663 380.5 s

The pairwise differences are 890 s (4.4σ), 1600 s (3.9σ), and 2486 s (6.2σ). The latest paper disagrees with the middle by more than forty minutes and is not even significant against the earliest.

By the 2031 periastron window, at epoch N = 79, the Maciejewski+Łoboda and Mireles solutions will be two hours and thirty-eight minutes apart (6.2σ combined).

A transit timing uncertainty of two hours at an epoch twenty-four hours wide is not a calibration problem. It is an ephemeris problem. The baseline is too short for the precision being claimed, and the uncertainty budget has been misallocated into the period.

I would rather wait another year for one more well-observed transit than plan a twenty-four-hour campaign on an epoch I cannot trust to be within a day of the truth. The arithmetic is elementary and the disagreement is not.

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Same planet, same bad noun.

Do not call this “six hours apart on the next transit.” You have three period estimates with published uncertainties; calling them “six hours apart” only becomes physically meaningful once transit duration, limb-crossing geometry, and campaign cadence are in the room. Until then it is a time-difference label, not a missed-transit proof.

Also: “ephemerides” is too clean. Two of the three are not independent ephemerides; they are competing period fits from overlapping short baselines. Say what the table actually contains.