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Hidden Transits: TOI-2285 b is a Warmer sub-Neptune Likely with a Super-Earth Companion

T0 review · 1 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash

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Pith's one-line read Hidden odd-numbered transits show that the sub-Neptune TOI-2285 b orbits its star in 13.64 days—half the 27.27-day period originally reported—and the same data hint at a 9.67-day super-Earth companion awaiting confirmation.

desk verdict The 13.64 d period correction is solid and worth publishing; the 9.67 d companion is honestly labeled a candidate, so treat the title's 'likely' as an overstatement, not the main result. read the letter →

arxiv 2505.22009 v1 pith:OX7HRPOZ submitted 2025-05-28 astro-ph.EP astro-ph.IM

Akihiko Fukui This is my paper
classification astro-ph.EPastro-ph.IM
keywords exoplanetssub-NeptuneMdwarfhoststarorbitalperiodharmonictransitsearchsuper-Earthcandidateequilibriumtemperature
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper reanalyzes nine sectors of space-based photometry for the M-dwarf host and concludes that the reported 27.27-day period of the sub-Neptune TOI-2285 b is a harmonic mistake: the true orbital period is 13.64 days, exactly half, with odd- and even-numbered transits of equal depth at the shorter period. That revision raises the planet's equilibrium temperature from 284 K to 358 K and its instellation from 1.54 to 3.91 times Earth's, though it remains among the few low-irradiated sub-Neptunes transiting a bright M dwarf. The same data reveal a second candidate signal at 9.67 days with a radius near 1.37 Earth radii, interpreted as a likely super-Earth companion that needs validation. The case matters because it shows how low signal-to-noise and a short data baseline can make a transit survey lock onto a period double the true one, urging caution for similar candidates.

What carries the argument

The machinery that carries the argument is Transit Least Squares, a period-search algorithm that folds a light curve over trial orbital periods and scores each folded transit signal; applying it to the combined nine sectors yields the 13.64-day peak, and a second run with the main planet masked yields the 9.67-day peak. The decisive check is the harmonic comparison: 13.64 days is exactly half of 27.27 days, and the original pipeline had missed the odd-numbered transits (epochs 1, 3, 17 in the early sectors) while retaining even-numbered ones, so it locked onto twice the true period. Additional machinery is a joint fit of transit and systematic-trend models to the undetrended light curves, producing radii, impact parameters, scaled semi-major axes, and transit ephemerides for both signals.

What would settle it

The next TESS sectors, or a ground-based photometric campaign, should see a transit every 13.64 days, including the odd-numbered epochs that were originally missing; if those odd transits do not recur at equal depth and duration, the period-halving interpretation is wrong.

Watch

Extended reading notes

Core claim

The central claim is that TOI-2285 b's orbital period is 13.635109 days, not the 27.27 days initially reported, so the planet is warmer and more irradiated than previously thought. This is established by a periodogram search on the full nine-sector light curve, which finds its strongest signal at 13.64 days with a detection efficiency of 54.2, far above threshold and much stronger than the signal at 27.27 days; the phase-folded transits at 13.64 days show consistent depth and duration between odd and even epochs, and no signal appears at phase 0.5 that would support a quarter-period solution. After masking that planet's transits, a second signal appears at 9.673341 days with a detection efficiency of 18, corresponding to a candidate planet of radius 1.37 Earth radii; the paper offers this as a super-Earth companion candidate explicitly requiring future validation. Adopting the original stellar parameters, the revised values are radius 1.77 Earth radii, instellation 3.91 times Earth's, and equilibrium temperature 358 K assuming a bond albedo of 0.3.

Load-bearing premise

The load-bearing premise is that the 9.67-day signal is a genuine super-Earth rather than a false positive from systematics or a periodogram alias; the paper itself marks this signal as requiring validation, and its detection efficiency of 18, though above the nominal threshold of 9, is well below the 54.2 of the main planet.

Editorial extensions

If this is right

  • TOI-2285 b should be removed from the short list of very-low-temperature sub-Neptunes at 284 K and instead be characterized at 358 K, changing any atmospheric or mass-loss inferences built on the old temperature.
  • The planet's true instellation of 3.91 S⊕ places it in the moderately irradiated regime, where atmospheric retention models make different predictions; the revised period also changes transit-depth ratios and any future atmospheric observation planning.
  • If the 9.67-day candidate is confirmed, TOI-2285 becomes a compact two-planet system around a bright M dwarf with a super-Earth and a sub-Neptune, inviting dynamical and formation studies.
  • The correction implies that other candidates with long periods, few transits, and low individual transit signal-to-noise may have similar period-doubling aliases; re-running searches at harmonic periods is a low-cost screen.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • A direct test the paper does not discuss is radial-velocity monitoring: the 13.64-day period should produce a Keplerian signal with an amplitude consistent with a ~1.8 Earth-radius planet around a 0.3 solar-mass star, and no independent Doppler period at 27.27 days.
  • The near 7:5 ratio between the proposed companion (9.67 d) and the refined planet (13.64 d) is not claimed by the paper; if the companion is confirmed, checking for a dynamical resonance would be a natural next step.
  • Other single-planet candidates whose periods were derived from only two or three TESS sectors could be re-examined at half-period harmonics; the paper's example suggests this should be routine before publishing long-period transiting planets.
  • The candidate's detection efficiency (18) is close to the nominal threshold (9), so future TESS sectors or ground-based photometry should recover the 9.67-day transit with independent data; if it does not, the companion claim will be dropped without undermining the period revision.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

1 major / 5 minor

Summary. This paper analyzes nine sectors of TESS photometry for TOI-2285 and finds that the originally reported 27.27 d orbital period of the sub-Neptune TOI-2285 b is an alias of the true 13.64 d period. The evidence is a TLS detection at 13.64 d with SDE=54.2, consistent odd/even transit depths, no transit at phase 0.5, and an independent SPOC TCE recovery. The revised period implies an equilibrium temperature of 358±8 K and instellation of 3.91 S⊕, moving the planet from the temperate to the warm category. The same data reveal a candidate 9.67 d, 1.37 R⊕ super-Earth (TOI-2285.02) that the paper itself states requires validation.

Significance. The period correction is significant because TOI-2285 b is a rare sub-Neptune transiting a bright M dwarf, and its revised irradiation changes its interpretation. The paper highlights a real risk of harmonic misidentification in TESS, which could affect other planets. The main result is well supported by public data and an independent pipeline, and the paper is concise and transparent. The companion candidate, by contrast, rests on a lower-significance signal and is explicitly advertised as needing validation; as such, its presence in the title is a concern that should be addressed before publication.

major comments (1)
  1. [Section 2 (TOI-2285.02 detection) and title/abstract] The 9.67 d signal is elevated to the title as a 'likely ... companion' and is assigned physical parameters (Rp=1.37 R⊕, Teq=402 K), but its only evidence is an SDE=18 TLS peak in the same TESS data and a SPOC TCE from the same data, both of which may share systematics. No odd/even consistency test, centroid shift test, false-positive probability, or independent data split is reported. The paper explicitly says the candidate 'requires validation' (Section 3), so the treatment is honest, but the prominence in the title overstates the confidence. Please either add at least one validation check (e.g., odd/even transit comparison or a window-function alias test) and a false-positive probability, or reframe the title and abstract to present TOI-2285.02 as an unconfirmed candidate without deriving headline physical parameters.
minor comments (5)
  1. [Abstract] The abstract states a companion radius of 1.5 R⊕, while Section 2 reports 1.37 (+0.16/−0.12) R⊕; please use the fitted value or round consistently.
  2. [Section 2 (fitting procedure)] The phrase 'undetrended PDCSAP light curves' is confusing because PDCSAP is by definition already detrended by the SPOC pipeline; please clarify whether additional detrending was applied or removed.
  3. [Figure 1(b)] The blue dashed lines are labeled as harmonics of the highest peaks, but the text does not explain how the harmonics were identified; add a sentence in the text or a note in the caption.
  4. [Section 3 (discussion of original misidentification)] The discussion would benefit from a brief quantitative check of the TESS window function to confirm that the 27.27 d alias arises naturally from the observing cadence and not from another periodic signal.
  5. [Section 2 (ephemerides)] The ephemeris for TOI-2285.02 is derived from the same data as the detection; the period uncertainty may be underestimated if the SDE=18 signal is not fully coherent across all sectors, so consider noting this caveat.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the period correction is derived directly from TESS light curves, and the companion candidate is explicitly flagged as requiring validation.

full rationale

The paper's central claim, that TOI-2285 b's orbital period is 13.64 d rather than 27.27 d, is obtained by applying the TLS periodogram to the full TESS PDCSAP light curves (Section 2, 'The strongest signal appeared at 13.64 d with SDE 54.2'). This is a direct search over the data, not a fit defined to reproduce the conclusion. The paper also reports consistency of odd/even transits, absence of signal at phase 0.5, and independent recovery by SPOC's TCE pipeline. The derived radii, instellations, and equilibrium temperatures use stellar parameters adopted from AF22 and the newly measured period; these are external inputs rather than circular outputs, and the new period actually corrects the author's earlier AF22 value. The companion candidate TOI-2285.02 is a separate TLS detection (SDE 18) with an explicit caveat that it 'requires validation' in future studies; it is not presented as a confirmed prediction, and its tentative status does not make the derivation circular. Self-citations (AF22 for stellar parameters, Fukui et al. 2021 for the fitting procedure) are methodological or reference inputs, not load-bearing uniqueness arguments or fitted quantities renamed as predictions. No equation defines one claimed result in terms of another claimed result, and no fitted parameter is later reported as an independent prediction. Therefore no significant circularity is found.

Assumptions & free parameters 7 free parameters · 5 assumptions · 0 invented entities

The paper introduces no new physical entities. It fits a standard transit model to public data, with the main inputs being the TESS light curves and the adopted stellar parameters from AF22. The free parameters are the usual transit fitted quantities, none of which are used in a way that forces the period conclusion.

free parameters (7)
  • Impact parameter b (TOI-2285 b) = 0.44 +0.32/-0.31
    Fitted in the transit model; affects derived transit geometry but not the period detection.
  • Scaled semi-major axis a/Rs (TOI-2285 b) = 43.1 +5.9/-11.8
    Fitted in the transit model; used with stellar parameters to derive instellation and temperature.
  • Planet-to-star radius ratio Rp/Rs (TOI-2285 b) = 0.0348 +0.0021/-0.0016
    Fitted in the transit model; used to compute planetary radius.
  • Impact parameter b (TOI-2285.02) = 0.55 +0.32/-0.38
    Fitted in the transit model for the companion candidate.
  • Scaled semi-major axis a/Rs (TOI-2285.02) = 42 +12/-17
    Fitted in the transit model for the companion candidate.
  • Planet-to-star radius ratio Rp/Rs (TOI-2285.02) = 0.0271 +0.0030/-0.0022
    Fitted in the transit model; used to compute the candidate's radius.
  • Quadratic limb-darkening coefficients u1, u2 = not reported
    Fitted with Gaussian priors; their values are not given in the paper, but they are part of the transit model.
assumptions (5)
  • domain assumption The TESS PDCSAP light curves are accurately calibrated and the detrending with Savitzky-Golay does not remove or distort transit signals.
    The entire analysis relies on these public light curves; no independent check of the detrending is provided.
  • domain assumption The transit model, including quadratic limb darkening and the systematic trend model from Fukui et al. 2021, adequately describes the data.
    The paper states it follows Fukui et al. 2021 but does not specify the systematic model in detail.
  • domain assumption Stellar parameters (radius, mass, effective temperature) from AF22 are accurate.
    These are adopted from the prior paper to convert transit depth to radius and to compute instellation and equilibrium temperature.
  • domain assumption A bond albedo of 0.3 is assumed when computing equilibrium temperature.
    The paper explicitly states this assumption; different albedos would change the temperature estimate.
  • standard math The TLS algorithm and SDE statistic correctly rank the true period against aliases.
    The period search relies on the TLS implementation and its detection threshold.

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Cite this review

Pith. "Pith review of Hidden Transits: TOI-2285 b is a Warmer sub-Neptune Likely with a Super-Earth Companion." pith.science (2026). https://pith.science/paper/OX7HRPOZ

@misc{pith2026250522009,
  author       = {Pith},
  title        = {Pith review of: Hidden Transits: TOI-2285 b is a Warmer sub-Neptune Likely with a Super-Earth Companion},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/OX7HRPOZ}},
  note         = {Machine review of arXiv:2505.22009}
}
abstract

TOI-2285 b is a sub-Neptune-sized planet orbiting a nearby M dwarf, discovered through the TESS photometric survey and ground-based follow-up observations. The planet was initially reported to have an orbital period of 27.27 d, making it one of the lowest temperature sub-Neptunes transiting a bright M dwarf. However, additional TESS data reveal that its true orbital period is 13.64 d, half the original value, resulting in a warmer equilibrium temperature (358 K) than previously estimated (284 K). The misidentification likely resulted from the low signal-to-noise ratio of individual transit signals and the limited number of transits observed by TESS at that time. This case highlights the importance of carefully considering harmonic solutions for similar cases. The additional TESS data also reveal another planetary candidate with an orbital period of 9.67 d and a radius of 1.5 $R_\oplus$, requiring validation in future studies.

Figures

Figures reproduced from arXiv: 2505.22009 by the authors.

Figure 1
Figure 1. (a) The sector-to-sector undetrended PDCSAP light curves of TOI-2285 binned by 30 minutes. The sector number is indicated on the left. The locations of even- and odd-number transits of TOI-2285 b are marked by orange and green, respectively, with transit epochs labeled. The locations of the transits of TOI-2285.02 are marked by blue. (b) The power spectra obtained from the first (top) and second (bottom) TLS analyse… view at source ↗

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