Detailed Architecture of the L 98-59 System and Confirmation of a Fifth Planet in the Habitable Zone
Bibliographic record
Abstract
Abstract The L 98-59 system, identified by TESS in 2019, features three transiting exoplanets in compact orbits of 2.253, 3.691, and 7.451 days around an M3V star, with an outer 12.83 day nontransiting planet confirmed in 2021 using ESPRESSO. The planets exhibit a diverse range of sizes (0.8–1.6 R ⊕ ), masses (0.5–3 M ⊕ ), and likely compositions (Earth-like to possibly water-rich), prompting atmospheric characterization studies with Hubble Space Telescope and JWST. Here, we analyze 16 new TESS sectors and improve radial velocity (RV) precision of archival ESPRESSO and HARPS data using a line-by-line framework, enabling stellar activity detrending via a novel differential temperature indicator. We refine the radii of L 98-59 b, c, and d to 0.837 ± 0.019 R ⊕ , 1.329 ± 0.029 R ⊕ , and 1.627 ± 0.041 R ⊕ , respectively. Combining RVs with transit timing variations (TTVs) of L 98-59 c and d from TESS and JWST provides unprecedented constraints on the masses and eccentricities of the planets. We report updated masses of 0.46 ± 0.11 M ⊕ for b, 2.00 ± 0.13 M ⊕ for c, and 1.64 ± 0.07 M ⊕ for d, and a minimum mass of 2.82 ± 0.19 M ⊕ for e. We additionally confirm L 98-59 f, a nontransiting super-Earth with a minimal mass of 2.80 ± 0.30 M ⊕ on a 23.06 day orbit inside the Habitable Zone. The TTVs of L 98-59 c and d (<3 minutes, P TTV = 396 days) constrain the eccentricities of all planets to near-circular orbits ( e ≲ 0.04). An internal structure analysis of the transiting planets reveals increasing water-mass fractions ( f H 2 O ) with orbital distance, reaching f H 2 O ≈ 0.16 for L 98-59 d. We predict eccentricity-induced tidal heating in L 98-59 b with heat fluxes comparable to those of Io, potentially driving volcanic activity.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".