TOI-1695 b: A Water World Orbiting an Early-M Dwarf in the Planet Radius Valley

Cherubim, Collin; Cloutier, Ryan; Charbonneau, David; Stockdale, Chris; Stassun, Keivan G.; Schwarz, Richard P.; Safonov, Boris; Mortier, A.; Lewin, Pablo; Latham, David W.; Horne, K.; Haywood, R. D.; Gonzales, Erica J.; Goliguzova, Maria V.; Collins, Karen A.; Ciardi, David R.; Bieryla, Allyson; Belinski, A. A.; Wohler, Bill; Watson, C. A.; Vanderspek, R.; Udry, S.; Sozzetti, A.; Ségransan, D.; Sasselov, Dimitar; Ricker, G.; Rice, Ken; Poretti, E.; Piotto, G.; Pepe, F.; Molinari, E.; Micela, G.; Mayor, M.; López‐Morales, Mercedes; Jenkins, Jon M.; Essack, Zahra; Dumusque, X.; Doty, J.; Colón, Knicole D.; Cameron, A. Collier; Buchhave, Lars A.

doi:10.3847/1538-3881/acbdfd

Cited by 13 publications

(10 citation statements)

References 102 publications

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“…Conversely, our models suggest that TOI 1695 b, once thought to be a water world based on its mass and radius measurements (Cherubim et al 2023), is less likely to be a water world, due to its relatively high density and short orbital period. However, that does not rule out the possibility of a low bulk content of H 2 O, as we have restricted our definition of water worlds to a lower limit of 30% of WMF.…”

Section: Discussion Of the Water-world Candidatesmentioning

confidence: 62%

Where Are the Water Worlds? Identifying Exo-water-worlds Using Models of Planet Formation and Atmospheric Evolution

Chakrabarty,

Mulders

2024

ApJ

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Planet formation models suggest that the small exoplanets that migrate from beyond the snowline of the protoplanetary disk likely contain water-ice-rich cores (∼50% by mass), also known as water worlds. While the observed radius valley of the Kepler planets is well explained by the atmospheric dichotomy of the rocky planets, precise measurements of the mass and radius of the transiting planets hint at the existence of these water worlds. However, observations cannot confirm the core compositions of those planets, owing to the degeneracy between the density of a bare water-ice-rich planet and the bulk density of a rocky planet with a thin atmosphere. We combine different formation models from the Genesis library with atmospheric escape models, such as photoevaporation and impact stripping, to simulate planetary systems consistent with the observed radius valley. We then explore the possibility of water worlds being present in the currently observed sample by comparing them with simulated planets in the mass–radius–orbital period space. We find that the migration models suggest ≳10% and ≳20% of the bare planets, i.e., planets without primordial H/He atmospheres, to be water-ice-rich around G- and M-type host stars, respectively, consistent with the mass–radius distributions of the observed planets. However, most of the water worlds are predicted to be outside a period of 10 days. A unique identification of water worlds through radial velocity and transmission spectroscopy is likely to be more successful when targeting such planets with longer orbital periods.

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Section: Discussion Of the Water-world Candidatesmentioning

confidence: 62%

Where Are the Water Worlds? Identifying Exo-water-worlds Using Models of Planet Formation and Atmospheric Evolution

Chakrabarty,

Mulders

2024

ApJ

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“…Alternatively, the planet could be purely rocky or with a water-mass fraction (WMF) of 10%-20%, clearly not as high as the water-rich (50% H 2 O) population suggested by Luque & Pallé (2022). Note that this latter scenario would involve a different formation mechanism, as suggested by recent studies (Cloutier & Menou 2020;Luque & Pallé 2022;Cherubim et al 2023;Piaulet et al 2023), where small planets around M dwarfs could directly accrete icy materials outside the water snow line before migrating inward, in which case sub-Neptunes would actually be water worlds rather than H/He-enveloped planets.…”

Section: New Density Measurementsmentioning

confidence: 89%

“…An Earth-like interior (CMF = 33%, WMF ∼ 0) overlaid by a solar mixture of hydrogen-helium contributing ∼0.1% of the mass and ∼10% of the radius could explain the density of LHS 1140 b. Here, we simulate the photoevaporation history of LHS 1140 b for 10 Gyr using the method of Cherubim et al (2023) to verify whether such a hydrogen-rich envelope could survive at the present day. These simulations take into account thermal evolution and photoevaporation (e.g., Owen & Wu 2017) from stellar extreme-ultraviolet (EUV; 10-130 nm) and core-powered atmospheric escape (e.g., Ginzburg et al 2018).…”

Section: Hydrogen-poor Mini-neptunementioning

confidence: 99%

New Mass and Radius Constraints on the LHS 1140 Planets: LHS 1140 b Is either a Temperate Mini-Neptune or a Water World

Cadieux,

Plotnykov,

Doyon

et al. 2024

ApJL

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The two-planet transiting system LHS 1140 has been extensively observed since its discovery in 2017, notably with Spitzer, HST, TESS, and ESPRESSO, placing strong constraints on the parameters of the M4.5 host star and its small temperate exoplanets, LHS 1140 b and c. Here, we reanalyze the ESPRESSO observations of LHS 1140 with the novel line-by-line framework designed to fully exploit the radial velocity content of a stellar spectrum while being resilient to outlier measurements. The improved radial velocities, combined with updated stellar parameters, consolidate our knowledge of the mass of LHS 1140 b (5.60 ± 0.19 M ⊕) and LHS 1140 c (1.91 ± 0.06 M ⊕) with an unprecedented precision of 3%. Transits from Spitzer, HST, and TESS are jointly analyzed for the first time, allowing us to refine the planetary radii of b (1.730 ± 0.025 R ⊕) and c (1.272 ± 0.026 R ⊕). Stellar abundance measurements of refractory elements (Fe, Mg, and Si) obtained with NIRPS are used to constrain the internal structure of LHS 1140 b. This planet is unlikely to be a rocky super-Earth, as previously reported, but rather a mini-Neptune with a ∼0.1% H/He envelope by mass or a water world with a water-mass fraction between 9% and 19%, depending on the atmospheric composition and relative abundance of Fe and Mg. While the mini-Neptune case would not be habitable, a water-abundant LHS 1140 b potentially has habitable surface conditions according to 3D global climate models, suggesting liquid water at the substellar point for atmospheres with relatively low CO2 concentration, from Earth-like to a few bars.

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“…Today, observational constraints on the bulk composition of sub-Neptunes are still inconclusive 47 – 49 , but with the help of the James Webb Space Telescope and the future ARIEL mission, we expect to find more evidence for either the water-rich or the H/He-dominated composition and advocate the investigation of sub-Neptune atmospheres to resolve the mysteries of the radius valley.…”

Section: Discussionmentioning

confidence: 99%

A radius valley between migrated steam worlds and evaporated rocky cores

Burn,

Mordasini,

Mishra

et al. 2024

Nat Astron

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The radius valley (or gap) in the observed distribution of exoplanet radii, which separates smaller super-Earths from larger sub-Neptunes, is a key feature that theoretical models must explain. Conventionally, it is interpreted as the result of the loss of primordial hydrogen and helium (H/He) envelopes atop rocky cores. However, planet formation models predict that water-rich planets migrate from cold regions outside the snowline towards the star. Assuming water to be in the form of solid ice in their interior, many of these planets would be located in the radius gap contradicting observations. Here we use an advanced coupled formation and evolution model that describes the planets’ growth and evolution starting from solid, moon-sized bodies in the protoplanetary disk to mature Gyr-old planetary systems. Employing new equations of state and interior structure models to treat water as vapour mixed with H/He, we naturally reproduce the valley at the observed location. The model results demonstrate that the observed radius valley can be interpreted as the separation of less massive, rocky super-Earths formed in situ from more massive, ex situ, water-rich sub-Neptunes. Furthermore, the occurrence drop at larger radii, the so-called radius cliff, is matched by planets with water-dominated envelopes. Our statistical approach shows that the synthetic distribution of radii quantitatively agrees with observations for close-in planets, but only if low-mass planets initially containing H/He lose their atmosphere due to photoevaporation, which populates the super-Earth peak with evaporated rocky cores. Therefore, we provide a hybrid theoretical explanation of the radius gap and cliff caused by both planet formation (orbital migration) as well as evolution (atmospheric escape).

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TOI-1695 b: A Water World Orbiting an Early-M Dwarf in the Planet Radius Valley

Cited by 13 publications

References 102 publications

Where Are the Water Worlds? Identifying Exo-water-worlds Using Models of Planet Formation and Atmospheric Evolution

Where Are the Water Worlds? Identifying Exo-water-worlds Using Models of Planet Formation and Atmospheric Evolution

New Mass and Radius Constraints on the LHS 1140 Planets: LHS 1140 b Is either a Temperate Mini-Neptune or a Water World

A radius valley between migrated steam worlds and evaporated rocky cores

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