ABSTRACT
We present the discovery of TOI-2136 b, a sub-Neptune planet transiting a nearby M4.5V-type star every 7.85 d, identified through photometric measurements from the Transiting Exoplanet ...Survey Satellite (TESS) mission. The host star is located 33 pc away with a radius of R* = 0.34 ± 0.02 R⊙, a mass of $0.34\pm 0.02 \, \mathrm{M}_{\odot }$, and an effective temperature of 3342 ± 100 K. We estimate its stellar rotation period to be 75 ± 5 d based on archival long-term photometry. We confirm and characterize the planet based on a series of ground-based multiwavelength photometry, high-angular-resolution imaging observations, and precise radial velocities from Canada–France–Hawaii Telescope (CFHT)/SpectroPolarimètre InfraROUge (SPIRou). Our joint analysis reveals that the planet has a radius of 2.20 ± 0.17 R⊕ and a mass of 6.4 ± 2.4 M⊕. The mass and radius of TOI-2136 b are consistent with a broad range of compositions, from water-ice to gas-dominated worlds. TOI-2136 b falls close to the radius valley for M dwarfs predicted by thermally driven atmospheric mass-loss models, making it an interesting target for future studies of its interior structure and atmospheric properties.
Context: TOI-2076 is a transiting three-planet system of sub-Neptunes orbiting a bright (G = 8.9 mag), young (\(340\pm80\) Myr) K-type star. Although a validated planetary system, the orbits of the ...two outer planets were unconstrained as only two non-consecutive transits were seen in TESS photometry. This left 11 and 7 possible period aliases for each. Aims: To reveal the true orbits of these two long-period planets, precise photometry targeted on the highest-probability period aliases is required. Long-term monitoring of transits in multi-planet systems can also help constrain planetary masses through TTV measurements. Methods: We used the MonoTools package to determine which aliases to follow, and then performed space-based and ground-based photometric follow-up of TOI-2076 c and d with CHEOPS, SAINT-EX, and LCO telescopes. Results: CHEOPS observations revealed a clear detection for TOI-2076 c at \(P=21.01538^{+0.00084}_{-0.00074}\) d, and allowed us to rule out three of the most likely period aliases for TOI-2076 d. Ground-based photometry further enabled us to rule out remaining aliases and confirm the \(P=35.12537\pm0.00067\) d alias. These observations also improved the radius precision of all three sub-Neptunes to \(2.518\pm0.036\), \(3.497\pm0.043\), and \(3.232\pm0.063\) \(R_\oplus\). Our observations also revealed a clear anti-correlated TTV signal between planets b and c likely caused by their proximity to the 2:1 resonance, while planets c and d appear close to a 5:3 period commensurability, although model degeneracy meant we were unable to retrieve robust TTV masses. Their inflated radii, likely due to extended H-He atmospheres, combined with low insolation makes all three planets excellent candidates for future comparative transmission spectroscopy with JWST.
We present the discovery of two exoplanets transiting TOI-836 (TIC 440887364) using data from TESS Sector 11 and Sector 38. TOI-836 is a bright (\(T = 8.5\) mag), high proper motion (\(\sim\,200\) ...mas yr\(^{-1}\)), low metallicity (Fe/H\(\approx\,-0.28\)) K-dwarf with a mass of \(0.68\pm0.05\) M\(_{\odot}\) and a radius of \(0.67\pm0.01\) R\(_{\odot}\). We obtain photometric follow-up observations with a variety of facilities, and we use these data-sets to determine that the inner planet, TOI-836 b, is a \(1.70\pm0.07\) R\(_{\oplus}\) super-Earth in a 3.82 day orbit, placing it directly within the so-called 'radius valley'. The outer planet, TOI-836 c, is a \(2.59\pm0.09\) R\(_{\oplus}\) mini-Neptune in an 8.60 day orbit. Radial velocity measurements reveal that TOI-836 b has a mass of \(4.5\pm0.9\) M\(_{\oplus}\) , while TOI-836 c has a mass of \(9.6\pm2.6\) M\(_{\oplus}\). Photometric observations show Transit Timing Variations (TTVs) on the order of 20 minutes for TOI-836 c, although there are no detectable TTVs for TOI-836 b. The TTVs of planet TOI-836 c may be caused by an undetected exterior planet.
We present the discovery of TOI-2136b, a sub-Neptune planet transiting every 7.85 days a nearby M4.5V-type star, identified through photometric measurements from the TESS mission. The host star is ...located \(33\) pc away with a radius of \(R_{\ast} = 0.34\pm0.02\ R_{\odot}\), a mass of \(0.34\pm0.02\ M_{\odot}\) and an effective temperature of \(\rm 3342\pm100\ K\). We estimate its stellar rotation period to be \(75\pm5\) days based on archival long-term photometry. We confirm and characterize the planet based on a series of ground-based multi-wavelength photometry, high-angular-resolution imaging observations, and precise radial velocities from CFHT/SPIRou. Our joint analysis reveals that the planet has a radius of \(2.19\pm0.17\ R_{\oplus}\), and a mass measurement of \(6.4\pm2.4\ M_{\oplus}\). The mass and radius of TOI2136b is consistent with a broad range of compositions, from water-ice to gas-dominated worlds. TOI-2136b falls close to the radius valley for low-mass stars predicted by the thermally driven atmospheric mass loss models, making it an interesting target for future studies of its interior structure and atmospheric properties.
Stars and planets both form by accreting material from a surrounding disk. Because they grow from the same material, theory predicts that there should be a relationship between their compositions. In ...this study, we search for a compositional link between rocky exoplanets and their host stars. We estimate the iron-mass fraction of rocky exoplanets from their masses and radii and compare it with the compositions of their host stars, which we assume reflect the compositions of the protoplanetary disks. We find a correlation (but not a 1:1 relationship) between these two quantities, with a slope of >4, which we interpret as being attributable to planet formation processes. Super-Earths and super-Mercuries appear to be distinct populations with differing compositions, implying differences in their formation processes.
\(Kepler\) revealed that roughly one-third of Sun-like stars host planets orbiting within 100 days and between the size of Earth and Neptune. How do these planets form, what are they made of, and do ...they represent a continuous population or multiple populations? To help address these questions, we began the Magellan-TESS Survey (MTS), which uses Magellan II/PFS to obtain radial velocity (RV) masses of 30 TESS-detected exoplanets and develops an analysis framework that connects observed planet distributions to underlying populations. In the past, small planet RV measurements have been challenging to obtain due to host star faintness and low RV semi-amplitudes, and challenging to interpret due to the potential biases in target selection and observation planning decisions. The MTS attempts to minimize these biases by focusing on bright TESS targets and employing a quantitative selection function and observing strategy. In this paper, we (1) describe our motivation and survey strategy, (2) present our first catalog of planet density constraints for 27 TESS Objects of Interest (TOIs; 22 in our population analysis sample, 12 that are members of the same systems), and (3) employ a hierarchical Bayesian model to produce preliminary constraints on the mass-radius (M-R) relation. We find that the biases causing previous M-R relations to predict fairly high masses at \(1~R_\oplus\) have been reduced. This work can inform more detailed studies of individual systems and offer a framework that can be applied to future RV surveys with the goal of population inferences.
The advent of a new generation of radial velocity instruments has allowed us to break the one Earth-mass barrier. We report a new milestone in this context with 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 to d). We announce the discovery of a fourth nontransiting planet with a minimum mass of 3.06_{-0.37}^{+0.33} MEarth 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} MEarth 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 10.6 pc 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 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. 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.
We report the discovery of HD 110113 b (TOI-755.01), a transiting mini-Neptune exoplanet on a 2.5-day orbit around the solar-analogue HD 110113 (Teff = 5730K). Using TESS photometry and HARPS radial ...velocities gathered by the NCORES program, we find HD 110113 b has a radius of \(2.05\pm0.12\) \(R_\oplus\) and a mass of \(4.55\pm0.62\) \(M_\oplus\). The resulting density of \(2.90^{+0.75}_{-0.59}\) g cm^{-3} is significantly lower than would be expected from a pure-rock world; therefore, HD 110113 b must be a mini-Neptune with a significant volatile atmosphere. The high incident flux places it within the so-called radius valley; however, HD 110113 b was able to hold onto a substantial (0.1-1\%) H-He atmosphere over its \(\sim4\) Gyr lifetime. Through a novel simultaneous gaussian process fit to multiple activity indicators, we were also able to fit for the strong stellar rotation signal with period \(20.8\pm1.2\) d from the RVs and confirm an additional non-transiting planet with a mass of \(10.5\pm1.2\) \(M_\oplus\) and a period of \(6.744^{+0.008}_{-0.009}\) d.
We present the bright (V\(_{mag} = 9.12\)), multi-planet system TOI-431, characterised with photometry and radial velocities. We estimate the stellar rotation period to be \(30.5 \pm 0.7\) days using ...archival photometry and radial velocities. TOI-431b is a super-Earth with a period of 0.49 days, a radius of 1.28 \(\pm\) 0.04 R\(_{\oplus}\), a mass of \(3.07 \pm 0.35\) M\(_{\oplus}\), and a density of \(8.0 \pm 1.0\) g cm\(^{-3}\); TOI-431d is a sub-Neptune with a period of 12.46 days, a radius of \(3.29 \pm 0.09\) R\(_{\oplus}\), a mass of \(9.90^{+1.53}_{-1.49}\) M\(_{\oplus}\), and a density of \(1.36 \pm 0.25\) g cm\(^{-3}\). We find a third planet, TOI-431c, in the HARPS radial velocity data, but it is not seen to transit in the TESS light curves. It has an \(M \sin i\) of \(2.83^{+0.41}_{-0.34}\) M\(_{\oplus}\), and a period of 4.85 days. TOI-431d likely has an extended atmosphere and is one of the most well-suited TESS discoveries for atmospheric characterisation, while the super-Earth TOI-431b may be a stripped core. These planets straddle the radius gap, presenting an interesting case-study for atmospheric evolution, and TOI-431b is a prime TESS discovery for the study of rocky planet phase curves.
The interiors of giant planets remain poorly understood. Even for the planets in the Solar System, difficulties in observation lead to large uncertainties in the properties of planetary cores. ...Exoplanets that have undergone rare evolutionary processes provide a route to understanding planetary interiors. Planets found in and near the typically barren hot-Neptune 'desert' (a region in mass-radius space that contains few planets) have proved to be particularly valuable in this regard. These planets include HD149026b, which is thought to have an unusually massive core, and recent discoveries such as LTT9779b and NGTS-4b, on which photoevaporation has removed a substantial part of their outer atmospheres. Here we report observations of the planet TOI-849b, which has a radius smaller than Neptune's but an anomalously large mass of \(39.1^{+2.7}_{-2.6}\) Earth masses and a density of \(5.2^{+0.7}_{-0.8}\) grams per cubic centimetre, similar to Earth's. Interior structure models suggest that any gaseous envelope of pure hydrogen and helium consists of no more than \(3.9^{+0.8}_{-0.9}\) per cent of the total planetary mass. The planet could have been a gas giant before undergoing extreme mass loss via thermal self-disruption or giant planet collisions, or it could have avoided substantial gas accretion, perhaps through gap opening or late formation. Although photoevaporation rates cannot account for the mass loss required to reduce a Jupiter-like gas giant, they can remove a small (a few Earth masses) hydrogen and helium envelope on timescales of several billion years, implying that any remaining atmosphere on TOI-849b is likely to be enriched by water or other volatiles from the planetary interior. We conclude that TOI-849b is the remnant core of a giant planet.
