![SpeX SXD spectrum of TOI-6981. The target spectrum (red) is shown alongside that of the M3.5V standard Luyten’s Star (grey), offset vertically for clarity. Regions of strong telluric absorption are shaded, and strong M-dwarf spectral features are indicated. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/10/TOI-6981.png?fit=1200%2C676&ssl=1)
[astro-ph.EP] We present TOI-6981 b, a cold (Teq= 170.0 +/-4.5 K, assuming an Earth-like albedo) sub-Neptune (Rb=2.40+/-0.10 R⊕) on a 60.8 day orbit around around its M4-type host star (R*=0.304 +/- 0.012 R⊙, M*=0.296 +/- 0.026 M⊙, Teff = 3215+/-58K), part of the SPECULOOS TEMPOS program.
We validate the planetary nature of TOI-6981 b using ground-based follow-up photometry, statistical validation and high-resolution spectroscopy. At such cold temperatures, TOI-6981 b sits roughly at the location of the water ice line (approx 170 K).
Given its orbital period and high transmission spectroscopy metric (TSM=51 +/- 9), it is one of the only planets in the sparsely populated cold planet regime amenable for atmospheric studies with JWST.
Therefore, TOI-6981 b could. possibly become a crucial benchmark in cold chemistry studies, tests of Hycean world hypotheses, and drawling parallels to the Solar System’s ice giants. Additionally, given its current orbit, it may provide insight into planetary formation and migration at or beyond the water ice line.
Planet radius vs orbital period for transiting approximately Neptunes or smaller (≤ 6 R⊕, same as Fig 7) but only for planets colder than Earth (≤255 K, Earth’s temperature assuming an albedo of 0.3). The colour bar shows the transmission spectroscopy metric (Kempton et al. 2018), recalculated for all planets. Planets are approximately split into their planet-types: ∼Earths, ∼super-Earths, ∼sub-Neptunes, ∼Neptunes (bottom to top). TOI6981 b is depicted by a diamond with a purple outline. Two other key planets, TOI-6478 b and LHS-1140 b are labelled for reference. — [astro-ph.EP]
Madison G. Scott, Amaury H.M.J Triaud, Emily K. Pass, Aleyna Adamson, Karen A. Collins, Khalid Barkaoui, Allyson Bieryla, Adam J. Burgasser, Mark E. Everett, Steve B. Howell, David W. Latham, Benjamin V. Rackham, Boris S. Safonov, Miquel Serra-Ricart, Abderahmane Soubkiou, Georgina Dransfield, Katharine Hesse, Pipa Fernandez de Diego, Emma Softich, Gregor Srdoc, Mathilde Timmermans, Jeroen Audenaert, Roi Alonso, Artem Y. Burdanov, Yasmin T. Davis, Fatemeh Davoudi, Julien de Wit, Shishir Dholakia, Elsa Ducrot, Michaël Gillon, Yilen Gomez Maqueo Chew, Matthew J. Hooton, Clàudia Janó-Muñoz, Emmanuel Jehin, Akanksha Khandelwal, Thomas R. Marriott, Peter P. Pedersen, Manuel Pichardo Marcano, Francisco J. Pozuelos, Rafael Rebolo-López, Manu Stalport, Alexander Venner, Selçuk Yalçinkaya, Francis Zong Lang, Sebastián Zúñiga-Fernández
Comments: second review received (MNRAS), minor comments
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2609.37597 [astro-ph.EP] (or arXiv:2609.37597v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.37597
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Submission history
From: Madison Scott
[v1] Tue, 29 Sep 2026 13:49:48 UTC (3,700 KB)
https://arxiv.org/abs/2609.37597
Astrobiology, Astrochemistry,
