A 36.34-day Sub-Neptune Candidate Transiting the Nearby K Dwarf TIC 402710280

We report a transiting sub-Neptune candidate with a period of 36.34 days around TIC 402710280, a K dwarf of TESS magnitude 9.24 at 66.8 pc that the Transiting Exoplanet Survey Satellite has observed only in full-frame images. The new analysis still awaits peer review, but it already lays out the central claim clearly.

The significance lies in exoplanet science has moved beyond the era of simple discovery into a period of comparative characterization. With more than five thousand confirmed planets known, the scientifically productive questions now concern atmospheric composition, internal structure, orbital history and the statistical properties of populations rather than the existence of individual worlds. A new detection or spectral measurement is most valuable when it adds a well-constrained data point to those comparative frameworks, not when it stands alone as an anecdote. We report a transiting sub-Neptune candidate with a period of 36.34 days around TIC 402710280 (TYC 9041-03677-1), a K dwarf of TESS magnitude 9.24 at 66. Four transits, recorded between 2021 and 2026 in Sectors 39, 93, 100 and 102 and reduced by three independent pipelines, share a depth of $2092 \pm 47$ ppm and a duration of $5.

Two of them fall on consecutive cycles, and every shorter period predicts transits in covered data that are absent at $\geq 18.6σ$. A transit model gives $R_p/R_\star = 0.0421^{+0.0007}_{-0.0005}$ and a stellar density consistent with the host's.

Difference-image centroids place the signal $1.5'' \pm 1.3''$ from the target. The only catalogued star close enough to contribute, a background star $3.5''$ away, would have to host an eclipsing binary whose eclipse shape is disfavoured for any.

No secondary eclipse is detected, and TRICERATOPS gives a false-positive probability of $0.003 \pm 0.004$. No high-resolution imaging exists, so companions within about $1''$ are constrained only by Gaia astrometry.

The broader interest lies in making the target less anecdotal and more comparable with the rest of the known planetary population. Population-level questions, such as the frequency of atmospheres around small rocky planets or the prevalence of water-rich worlds in the habitable zone, require well-characterized individual data points before statistical patterns become meaningful. Each new planet with a measured radius, mass and, ideally, atmospheric constraint is a brick in that larger structure, and the accumulation of bricks eventually allows theorists to test formation models against real distributions rather than projections.

Quick-Look Pipeline light curves reproduce the 29-min excess in the interval between the two 2026 transits, so it does not arise in our photometry. The light curve also contains a $407 \pm 26$ ppm signal with a period of 3.78 days whose source, the target or the background star, the present data cannot identify.

Because this is still a preprint, the result should be read with genuine interest and proportionate caution. Peer review is not a guarantee of correctness, but it is a process that forces authors to respond to technical criticism from specialists who have no stake in a particular outcome. Preprints that survive that process, often with substantive revisions, emerge with a stronger evidential base than the version that first appeared. Until that stage is complete, the responsible reading keeps uncertainty explicitly visible rather than treating the claims as established findings.

The next step is to improve independent constraints on the mass, radius, atmospheric composition and orbital dynamics of the target. Transmission spectroscopy with JWST, radial velocity campaigns with high-resolution ground-based spectrographs and phase-curve measurements from space photometry represent the observational toolkit that can move characterization from plausible to robust. That convergence of techniques is the standard the community now expects before a planetary atmosphere result is treated as confirmed. Until peer review and independent follow-up address those open questions, skepticism is not a failure of appreciation for the work; it is part of how science decides what to keep.

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