A Second Terrestrial Planet Orbiting the Nearby M Dwarf LHS 1140

Abstract

LHS 1140 is a nearby mid-M dwarf known to host a temperate rocky super-Earth (LHS 1140 b) on a 24.737-day orbit. Based on photometric observations by MEarth and Spitzer as well as Doppler spectroscopy from HARPS, we report the discovery of 2 Ment et al.an additional transiting rocky companion (LHS 1140 c) with a mass of 1.81 ± 0.39 M ⊕ and a radius of 1.282 ± 0.024 R ⊕ on a tighter, 3.77795-day orbit. We also obtain more precise estimates of the mass and radius of LHS 1140 b to be 6.98 ± 0.89 M ⊕ and 1.727 ± 0.032 R ⊕ . The mean densities of planets b and c are 7.5 ± 1.0 g/cm 3 and 4.7 ± 1.1 g/cm 3 , respectively, both consistent with the Earth's ratio of iron to magnesium silicate. The orbital eccentricities of LHS 1140 b and c are consistent with circular orbits and constrained to be below 0.06 and 0.31, respectively, with 90% confidence. Because the orbits of the two planets are co-planar and because we know from previous analyses of Kepler data that compact systems of small planets orbiting M dwarfs are commonplace, a search for more transiting planets in the LHS 1140 system could be fruitful. LHS 1140 c is one of the few known nearby terrestrial planets whose atmosphere could be studied with the upcoming James Webb Space Telescope.

Tidal evolution of exoplanetary systems hosting potentially habitable exoplanets. The cases of LHS-1140 b-c and K2-18 b-c

“…We analysed the spin and orbit evolution of the system by considering that the two planets have a small value of the relaxation factor (which is consistent with the discussions presented in Dittmann et al (2017) and Ment et al (2019) regarding the planets compositions and internal structure models). The results of the numerical experiments have shown that the eccentricity decay of both planets is ruled by the eccentricity decay of the inner planet.…”

“…The results of Fig. 1 show that, if the eccentricities of LHS-1140 b and c are close to the upper boundary values estimated by Ment et al (2019), the rotation of the planets is most likely not synchronous if we suppose that the planets had a past fast rotation rate with Ω n.…”

“…Parameter value Dittmann et al (2017)., while the hypothesis of a rocky LHS-1140 c with a magnesium and silicate core was discussed by Ment et al (2019). Table 1 shows the values of some physical and orbital parameters taken from Ment et al (2019), which were used in this work to study the spin-orbit evolution of the system.…”

“…Tidal interactions slow down the body's rotation until an equilibrium configuration of the rotation is reached, where Ω = 0, i.e the secular variation of the rotation is zero (the same mathematical condition holds for the secular torque, since it is proportional to Ω). We now explore the possible spin-orbit resonances for LHS-1140 c and b by supposing that their current eccentricities are near the upper boundary values estimated by Ment et al (2019), namely e b = 0.06 and e c = 0.31 (cf. Table 1).…”

The L 98-59 System: Three Transiting, Terrestrial-size Planets Orbiting a Nearby M Dwarf

“…The SPOC simple aperture photometry (SAP) and presearch data conditioned (PDCSAP) light curves (Smith et al 2012;Stumpe et al 2014) of L 98-59 are shown in Figure 1. We use the methods appropriate for M dwarfs previously used by Berta-Thompson et al (2015), Dittmann et al (2017), and Ment et al (2019) to determine the stellar parameters of the host star, and adopt these parameters throughout our analysis. We estimate the mass of the star using the mass-luminosity relation in the K band from Benedict et al (2016) to be 0.313±0.014 M e .…”