Warm terrestrial planet with half the mass of Venus transiting a nearby star

Abstract

In recent years, the advent of a new generation of radial velocity instruments has allowed us to detect planets with increasingly lower mass and to break the one Earth-mass barrier. Here we report a new milestone in this context by announcing the detection of the lowest-mass planet measured so far using radial velocities: L 98-59 b, a rocky planet with half the mass of Venus. It is part of a system composed of three known transiting terrestrial planets (planets b–d). We announce the discovery of a fourth nontransiting planet with a minimum mass of 3.06−0.37+0.33 M⊕ and an orbital period of 12.796−0.019+0.020 days and report indications for the presence of a fifth nontransiting terrestrial planet. With a minimum mass of 2.46−0.82+0.66 M⊕ and an orbital period 23.15−0.17+0.60 days, this planet, if confirmed, would sit in the middle of the habitable zone of the L 98-59 system. L 98-59 is a bright M dwarf located 10.6ṗc away. Positioned at the border of the continuous viewing zone of the James Webb Space Telescope, this system is destined to become a corner stone for comparative exoplanetology of terrestrial planets. The three transiting planets have transmission spectrum metrics ranging from 49 to 255, which undoubtedly makes them prime targets for an atmospheric characterization with the James Webb Space Telescope, the Hubble Space Telescope, Ariel, or ground-based facilities such as NIRPS or ESPRESSO. With an equilibrium temperature ranging from 416 to 627 K, they offer a unique opportunity to study the diversity of warm terrestrial planets without the unknowns associated with different host stars. L 98-59 b and c have densities of 3.6−1.5+1.4 and 4.57−0.85+0.77 g cm−3, respectively, and have very similar bulk compositions with a small iron core that represents only 12 to 14% of the total mass, and a small amount of water. However, with a density of 2.95−0.51+0.79 g cm−3 and despite a similar core mass fraction, up to 30% of the mass of L 98-59 d might be water.

Scaling K2. V. Statistical Validation of 60 New Exoplanets From K2 Campaigns 2–18

“…This would result in a measurable RV semiamplitude (K ∼ 2.4 m s −1 ), but predicts TSM (∼30) and ESM (∼2.4) values that indicate atmospheric follow-up would be challenging, compared to the thresholds recommended by Kempton et al (2018). Given its relatively small size and relatively small host star, the TSM value does make it somewhat comparable to other close-in super-Earth planets, such as LTT 1445 A b (TSM ∼ 40; Winters et al 2019) and L 98-59 c (TSM ∼ 34; Demangeon et al 2021).…”

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

“…Figure 18 also highlights three other systems presenting similarities with TOI-1452b, namely, TOI-1235b (Cloutier et al 2020b), L 98-59 d (Cloutier et al 2019;Demangeon et al 2021), and LHS 1140b(Dittmann et al 2017Lillo-Box et al 2020). All four planets have a similar size, while spanning a large interval in periods.…”

“…All seven host stars in Table10have T eff < 4000 K (or average T eff of 3225 K), confirming the high interest of M dwarfs for planetary atmospheric characterization. Note that the high-value target L 98-59 d (TSM above 200;Cloutier et al 2019;Demangeon et al 2021) was just barely excluded from Table…”

The TESS-Keck Survey. XI. Mass Measurements for Four Transiting Sub-Neptunes Orbiting K Dwarf TOI–1246

“…About 15% of TESS Objects of Interest (TOIs) are predicted to be in systems with multiple transiting planets (Huang et al 2018). While 34 TESS systems host multiple confirmed planets, only four systems host four or more transiting planets: HD 108236 (Bonfanti et al 2021), L98-59 (Demangeon et al 2021), TOI-178 (Leleu et al 2021), and TOI-561 (Lacedelli et al 2021;Weiss et al 2021). In this work, we add to this growing-but currently small-sample.…”