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REVIEW 2 major objections 2 minor 51 references

In Search of Decay: An Analysis of Transit Times of Hot Jupiters in Main Sequence and Post-Main Sequence Systems

T0 review · 2 major / 2 minor · reviewed 2026-08-05 · deepseek-v4-flash

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Pith's one-line read Eight hot Jupiters show orbital period decay at 3σ, and the inferred tidal quality factor is orders of magnitude below theory.

desk verdict Useful transit-timing survey idea, but the eight 3σ decay claims are not credible from the abstract alone, and the supplied full text is a different paper. read the letter →

arxiv 2508.18355 v1 pith:RZRJGAVG submitted 2025-08-25 astro-ph.EP astro-ph.SR

Noah Sodickson , Samuel Grunblatt This is my paper
classification astro-ph.EPastro-ph.SR
keywords hotJupitersorbitaldecaytransittimingvariationtidalqualityfactorTESSBayesianInformationCriterionstellarevolutionpost-main-sequencestars
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 makes a new transit-timing search for orbital decay in 54 hot Jupiter systems whose host stars span main-sequence and post-main-sequence evolution. It adds fresh TESS mid-transit times and compares each system's ephemeris to a linear one using the Bayesian Information Criterion, identifying 25 systems with period decreases and 8 whose decreases are 3σ inconsistent with zero. It then uses the period changes to set lower limits on the modified stellar tidal quality factor Q*′, a measure of how efficiently the star dissipates tidal energy. The paper's central result is that these limits are orders of magnitude below theoretical expectations for both the full sample and evolved stars, meaning stars appear to dissipate tidal energy far more quickly than current models permit.

What carries the argument

The central tool is a comparison of linear versus quadratic ephemerides for each system's TESS mid-transit times, scored by the Bayesian Information Criterion. A BIC preference for the quadratic ephemeris with a negative coefficient is taken as evidence of orbital period decay. The period change is then converted into the modified stellar tidal quality factor Q*′ through standard tidal relations, so the observed timing drifts constrain how efficiently each host star dissipates tidal energy.

What would settle it

Recompute each of the eight candidates' transit times with an explicit spot-crossing and stellar-activity model, then reject any system whose 3σ decrease disappears; WASP-4 serves as the calibration case because its earlier claimed decay was later attributed to activity. Also check whether the decreasing-period detections cluster in particular TESS sectors—if they do, a sector-level timing systematic is the more likely explanation.

Watch

Extended reading notes

Core claim

The paper analyzes mid-transit times from TESS for 54 hot Jupiter systems spanning main-sequence and evolved (post-main-sequence) hosts. It fits each system to a linear ephemeris and a quadratic ephemeris, using the Bayesian Information Criterion to decide which is preferred. It reports that 25 systems show evidence of a period decrease and that 8 (CoRoT-2, TrES-5, WASP-4, WASP-12, WASP-19, WASP-45, WASP-99, XO-3) show decreases inconsistent with 0 at ≥3σ. Converting the period changes to the modified stellar tidal quality factor Q*′, the paper finds lower limits on Q*′ that are orders of magnitude below standard theoretical expectations, both for the full sample and for evolved stars, with

Load-bearing premise

The measured transit times and quoted uncertainties faithfully represent each planet's orbital clock, so a BIC-preferred period decrease is genuine decay rather than a product of spot crossings, stellar activity, or instrument systematics.

Editorial extensions

If this is right

  • These eight systems become high-priority targets for continued timing, because confirmation would firmly establish orbital decay as an observable population rather than a one-off event.
  • The empirical Q*′ constraints imply that stars dissipate tidal energy much more efficiently than current tidal models assume.
  • Evolved stars do not show weaker dissipation; if anything their lower limit on Q*′ is slightly lower, meaning post-main-sequence engulfment timescales may be shorter than predicted.
  • The BIC-based screening method provides a template for searching large transit-timing datasets for decay candidates.
  • A multi-system decay sample would allow tests of how tidal dissipation depends on stellar mass, radius, and evolutionary state rather than treating Q*′ as a single universal number.

Reading between the lines

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

  • Because 3σ across 54 systems implies roughly one expected false positive from Gaussian noise alone, the true count of decaying systems may be smaller than eight; the paper's own caveat about unreliable timings points in the same direction.
  • If the inferred Q*′ lower limits hold, tidal dissipation prescriptions in population-synthesis and planet-engulfment models would need recalibration toward much lower Q*′.
  • A direct follow-up: fold earlier ground- and space-based transit epochs for the eight candidates into the same BIC analysis; the quadratic trends that survive are the ones worth calling genuine decay.
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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

2 major / 2 minor

Summary. The manuscript as submitted is arXiv:2508.18355, titled 'In Search of Decay: An Analysis of Transit Times of Hot Jupiters in Main Sequence and Post-Main Sequence Systems.' The abstract describes a transit-timing analysis of 54 hot Jupiter systems, reporting 25 systems with evidence of orbital period decrease and 8 with a decrease inconsistent with zero at 3σ (CoRoT-2, TrES-5, WASP-4, WASP-12, WASP-19, WASP-45, WASP-99, and XO-3). It also derives lower limits on the modified stellar tidal quality factor Q*' for evolved and full samples. However, the full text provided is a completely different paper, 'Constraints on Long-Range Forces in De Sitter Space' by Baumann et al., with no mention of transits, hot Jupiters, or tidal decay. The body of the manuscript therefore does not support the abstract's claims, and no methods, data, or analysis are present to evaluate.

Significance. If the claimed analysis existed and were correct, it would be a valuable contribution to the study of tidal orbital decay of hot Jupiters and the empirical calibration of Q*'. The list of eight 3σ decay candidates and the order-of-magnitude constraints on Q*' would be of significant interest to the exoplanet community. However, the manuscript as submitted is internally inconsistent: the abstract and the body are about entirely different subjects. Consequently, the significance cannot be assessed from the submitted text, and the paper in its current form has no scientific content matching the abstract.

major comments (2)
  1. [Full text] The full text of the manuscript is not the paper described in the abstract. It is 'Constraints on Long-Range Forces in De Sitter Space' by Baumann et al., a hep-th paper on partially massless fields. None of the transit-time analysis, the 54 systems, the BIC fits, the Q*' relations, or the candidate list appear in the body. This is a load-bearing mismatch: the abstract's conclusions have no supporting data, methodology, or derivations in the manuscript. The submission is thus internally inconsistent and cannot be reviewed as a scientific paper.
  2. [Abstract] Even taken alone, the abstract's central claim—'8 showed evidence of a decrease that was inconsistent with 0 by three standard deviations'—is immediately qualified by the sentence 'the significance of some of these detections may be influenced by unreliable transit time measurements.' The abstract does not describe any procedure for distinguishing true orbital decay from stellar activity (e.g., spot crossing), apsidal precession, or systematics. The reader's concern about WASP-4, a system previously retracted as a decay candidate due to activity, is well-founded; WASP-4 is on the list. Without a demonstrated control for these effects, the detection count and the derived Q*' lower limits inherit substantial uncertainty. The manuscript provides no method to assess this.
minor comments (2)
  1. [Abstract] The symbol Q*' is used without definition in the abstract; while standard in the field, a brief definition would improve accessibility.
  2. [Title/Abstract] The title and abstract promise an analysis of main-sequence and post-main-sequence systems, but no such distinction is defined in the abstract; the full text does not clarify.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity; derivation reduces to direct fits and external Q* relations.

full rationale

The abstract's derivation chain is observational and external-benchmark-based: mid-transit times are measured data; linear and quadratic ephemerides are fit to those times; the period-decrease detections are the fitted coefficients of the quadratic models; and Q*' values are derived afterward from 'widely tested theoretical relations,' which are external to the paper rather than quantities defined by the fit. No prediction is a refitted constant, no self-citation is invoked as a load-bearing premise, and no internal uniqueness theorem is used. The abstract's caveat about unreliable transit time measurements is a correctness or robustness concern, not a circularity concern. The supplied 'FULL TEXT' is in fact a separate paper on de Sitter space with different authors, and it has no bearing on the transit-timing derivation; it cannot be used to establish circularity here. Therefore no circular step can be identified from the provided material.

Assumptions & free parameters 0 free parameters · 3 assumptions · 0 invented entities

From the abstract alone, no hand-tuned or ad hoc fitted theory parameters are visible. The per-system ephemeris coefficients (period, epoch, period derivative) are fitted to data, but those are the measurements themselves rather than free parameters of the central claim. Q*' values come from external theoretical relations imported from the prior literature, and no new physical entities are proposed. The three axioms listed are the load-bearing domain assumptions on which the detection list and the Q*' constraints rest.

assumptions (3)
  • domain assumption A quadratic ephemeris (constant period derivative) describes genuine tidal orbital decay, and BIC-preferred departures from a linear ephemeris are not caused by stellar activity, apsidal precession, or light-travel-time effects.
    The abstract interprets decreasing periods as decay candidates from BIC model selection. Historical cases in this subfield (apparent WASP-4 decay later attributed to stellar activity) show this assumption is frequently violated; per-system vetting would be required.
  • domain assumption The 'widely tested theoretical relations' linking observed period change to Q*' remain valid for post-main-sequence host stars.
    The abstract computes Q*' via these relations and then compares limits for evolved versus all systems. Evolved star structures (convective envelopes, different tidal dissipation channels) may alter the relation, which would invalidate the comparative constraint.
  • domain assumption TESS-derived mid-transit times and their reported uncertainties are accurate across all 54 systems.
    The abstract's own caveat, 'the significance of some of these detections may be influenced by unreliable transit time measurements', admits this premise is at least partially violated, and the three-sigma detections are only as strong as these uncertainties.

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Cite this review

Pith. "Pith review of In Search of Decay: An Analysis of Transit Times of Hot Jupiters in Main Sequence and Post-Main Sequence Systems." pith.science (2026). https://pith.science/paper/RZRJGAVG

@misc{pith2026250818355,
  author       = {Pith},
  title        = {Pith review of: In Search of Decay: An Analysis of Transit Times of Hot Jupiters in Main Sequence and Post-Main Sequence Systems},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/RZRJGAVG}},
  note         = {Machine review of arXiv:2508.18355}
}
abstract

Tidal interactions are one of the primary drivers of orbital evolution for massive planets with short orbital periods. Tidal dissipation within host stars can cause the orbits of such planets to decay. However, the mechanisms of tidal dissipation are difficult to probe. Generally, tidal dissipation is parameterized by the modified stellar tidal quality factor, or $Q_{*}^{'}$, but the lack of observational evidence of orbital decay to confirm dissipation theories has resulted in orders of magnitude of uncertainty in $Q_{*}^{'}$. We present a new transit timing analysis of 54 systems with varying stellar evolutionary states in an attempt to search for orbital decay across multiple stages of stellar evolution. For each system, we obtained mid-transit times from new TESS data and evaluated potential departures from a linear ephemeris using the Bayesian Information Criterion. We then determined tidal quality factors using widely tested theoretical relations. Of the systems studied, 25 showed evidence of a decrease in orbital period over time and 8 showed evidence of a decrease that was inconsistent with 0 by three standard deviations: CoRoT-2, TrES-5, WASP-4, WASP-12, WASP-19, WASP-45, WASP-99, and XO-3. However, the significance of some of these detections may be influenced by unreliable transit time measurements. Similarly, we see that the lower limit on $Q_{*}^{'}$ for evolved systems is marginally lower than it is for the sample of all systems, though both limits are orders of magnitude below the expected theoretical values for both samples. These new constraints on transit times and $Q_{*}^{'}$ values will help to narrow the search for orbital decay in the future and place important constraints on current theories of star-planet interactions.

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