TOI-1452 b: SPIRou and TESS Reveal a Super-Earth in a Temperate Orbit Transiting an M4 Dwarf

Abstract

Exploring the properties of exoplanets near or inside the radius valley provides insight on the transition from the rocky super-Earths to the larger, hydrogen-rich atmosphere mini-Neptunes. Here, we report the discovery of TOI-1452b, a transiting super-Earth (R p = 1.67 ± 0.07 R ⊕) in an 11.1 day temperate orbit (T eq = 326 ± 7 K) around the primary member (H = 10.0, T eff = 3185 ± 50 K) of a nearby visual-binary M dwarf. The transits were first detected by the Transiting Exoplanet Survey Satellite, then successfully isolated between the two 3.″2 companions with ground-based photometry from the Observatoire du Mont-Mégantic and MuSCAT3. The planetary nature of TOI-1452b was established through high-precision velocimetry with the near-infrared SPIRou spectropolarimeter as part of the ongoing SPIRou Legacy Survey. The measured planetary mass (4.8 ± 1.3 M ⊕) and inferred bulk density ( 5.6 − 1.6 + 1.8 g cm−3) is suggestive of a rocky core surrounded by a volatile-rich envelope. More quantitatively, the mass and radius of TOI-1452b, combined with the stellar abundance of refractory elements (Fe, Mg, and Si) measured by SPIRou, is consistent with a core-mass fraction of 18% ± 6% and a water-mass fraction of 22 − 13 + 21 %. The water world candidate TOI-1452b is a prime target for future atmospheric characterization with JWST, featuring a transmission spectroscopy metric similar to other well-known temperate small planets such as LHS 1140b and K2-18 b. The system is located near Webb’s northern continuous viewing zone, implying that is can be followed at almost any moment of the year.

A New Definition of Exoplanet Habitability: Introducing the Photosynthetic Habitable Zone

“…Additionally, we also plot three recently identified water world candidates, Kepler-138 c and d (Piaulet et al 2023) and TOI-1452 b (Cadieux et al 2022). While these fall outside the HZ, Kepler-138 d and TOI-1452 b fall inside the PZ.…”

Exoplanet science with SPIRou: near-infrared precision velocimetry and spectropolarimetry

“…More details on the properties of these systems, including the magnetic topology of their host stars, can be found in relevant Refs. [10,11]. • Multiple systems around low-mass stars.…”

Rocky Planet or Water World? Observability of Low-density Lava World Atmospheres

“…The radii of such planets follow a bimodal distribution, with peaks at ∼1.3 R ⊕ and ∼2.4 R ⊕ , which can be explained by smaller rocky planets and larger planets with hydrogen-rich envelopes, respectively (Fulton et al 2017;Owen & Wu 2017;Ginzburg et al 2018;Mordasini 2020). Meanwhile, mass measurements have revealed a growing population of planets with intermediate bulk densities (e.g., Zeng et al 2021;Brinkman et al 2023;Cadieux et al 2022;Diamond-Lowe et al 2022;Luque & Pallé 2022;Piaulet et al 2023), which we refer to as low-density super-Earths (shaded blue region in Figure 1). The radii of these planets are too large to be explained by a rocky Earth-like interior composition but they are small enough that they do not necessarily require a hydrogen-rich envelope to explain their low bulk density.…”