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A low-mass star that is just 12 parsecs away from Earth is shown to be transited by an Earth-sized planet, GJ 1132b, which probably has a rock/iron composition and might support a substantial atmosphere. GJ1132b — a nearby rocky, Earth-sized planet Zachory Berta-Thompson et al . report observations of GJ 1132b, a 1.2 Earth radius planet transiting a small star only 12 parsecs away. The Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like rock/iron composition. The planet is too hot to be habitable but is cool enough to support a substantial atmosphere. Because the host star is nearby, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere. M-dwarf stars—hydrogen-burning stars that are smaller than 60 per cent of the size of the Sun—are the most common class of star in our Galaxy and outnumber Sun-like stars by a ratio of 12:1. Recent results have shown that M dwarfs host Earth-sized planets in great numbers 1 , 2 : the average number of M-dwarf planets that are between 0.5 to 1.5 times the size of Earth is at least 1.4 per star 3 . The nearest such planets known to transit their star are 39 parsecs away 4 , too distant for detailed follow-up observations to measure the planetary masses or to study their atmospheres. Here we report observations of GJ 1132b, a planet with a size of 1.2 Earth radii that is transiting a small star 12 parsecs away. Our Doppler mass measurement of GJ 1132b yields a density consistent with an Earth-like bulk composition, similar to the compositions of the six known exoplanets with masses less than six times that of the Earth and precisely measured densities 5 , 6 , 7 , 8 , 9 , 10 , 11 . Receiving 19 times more stellar radiation than the Earth, the planet is too hot to be habitable but is cool enough to support a substantial atmosphere, one that has probably been considerably depleted of hydrogen. Because the host star is nearby and only 21 per cent the radius of the Sun, existing and upcoming telescopes will be able to observe the composition and dynamics of the planetary atmosphere.

Mapping the three-dimensional trajectory of a Neptune-mass exoplanet across the disk of its cool star reveals that its orbit is nearly perpendicular to the stellar equator, implying the existence of a yet-undetected outer companion planet. Eccentric planet spinoff GJ 436b is a Neptune-sized planet orbiting a cool M dwarf star. Rather unusually, it has a large exosphere—the outer layer of the atmosphere that merges into space. Vincent Bourrier and colleagues have determined the orbit of the planet to be very eccentric and almost perpendicular to the spin of its parent star, which is unusual for orbits around a cool star. Under normal conditions, the orbit of a planet is fairly closely aligned with the star's spin, as is true in the Solar System. The authors suggest that the planet was dynamically scattered into its present orbit by another—as yet unseen—planet and that its movement closer to the cool star could have caused the atmospheric escape that drives such an enormous exosphere. The angle between the spin of a star and the orbital planes of its planets traces the history of the planetary system. Exoplanets orbiting close to cool stars are expected to be on circular, aligned orbits because of strong tidal interactions with the stellar convective envelope 1 . Spin–orbit alignment can be measured when the planet transits its star, but such ground-based spectroscopic measurements are challenging for cool, slowly rotating stars 2 . Here we report the three-dimensional characterization of the trajectory of an exoplanet around an M dwarf star, derived by mapping the spectrum of the stellar photosphere along the chord transited by the planet 3 . We find that the eccentric orbit of the Neptune-mass exoplanet GJ 436b is nearly perpendicular to the stellar equator. Both eccentricity and misalignment, surprising around a cool star, can result from dynamical interactions (via Kozai migration 4 ) with a yet-undetected outer companion. This inward migration of GJ 436b could have triggered the atmospheric escape that now sustains its giant exosphere 5 .

An Earth-sized planet is observed orbiting a nearby star within the liquid-water, habitable zone, the atmospheric composition of which could be determined from future observations. Super-Earth rocks around cool star Planets cause a dip in the light received when they pass in front of their parent stars. M stars have masses less than 60 per cent that of the Sun, and account for three-quarters of our Galaxy's stellar population. Seven Earth-sized planets are known to transit such a star, TRAPPIST-1, at 12 parsecs from Earth, but their masses and therefore their densities are rather poorly constrained. Jason Dittman et al . report observations of LHS 1140b, a planet with a radius 1.4 times that of Earth that is transiting an M dwarf star 12 parsecs from Earth and receiving sufficient insolation to place it in the liquid-water, 'habitable zone'. They measure the mass to be 6.6 times that of Earth, which suggests a rocky bulk composition. M dwarf stars, which have masses less than 60 per cent that of the Sun, make up 75 per cent of the population of the stars in the Galaxy 1 . The atmospheres of orbiting Earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars 2 , 3 . Statistical results suggest that the nearest transiting Earth-sized planet in the liquid-water, habitable zone of an M dwarf star is probably around 10.5 parsecs away 4 . A temperate planet has been discovered orbiting Proxima Centauri, the closest M dwarf 5 , but it probably does not transit and its true mass is unknown. Seven Earth-sized planets transit the very low-mass star TRAPPIST-1, which is 12 parsecs away 6 , 7 , but their masses and, particularly, their densities are poorly constrained. Here we report observations of LHS 1140b, a planet with a radius of 1.4 Earth radii transiting a small, cool star (LHS 1140) 12 parsecs away. We measure the mass of the planet to be 6.6 times that of Earth, consistent with a rocky bulk composition. LHS 1140b receives an insolation of 0.46 times that of Earth, placing it within the liquid-water, habitable zone 8 . With 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. The circular orbit is unlikely to be the result of tides and therefore was probably present at formation. Given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth 9 , 10 . Because LHS 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future 2 , 3 .

We present an intensive effort to refine the mass and orbit of the enveloped terrestrial planet GJ 1214 b using 165 radial velocity (RV) measurements taken with the HARPS spectrograph over a period of ten years. We conduct a joint analysis of the RVs with archival Spitzer/IRAC transits and measure a planetary mass and radius of \\(8.17\\pm 0.43 M_{\\oplus}\\) and \\(2.742^{+0.050}_{-0.053} R_{\\oplus}\\). Assuming GJ 1214 b is an Earth-like core surrounded by a H/He envelope, we measure an envelope mass fraction of \\(X_{\\rm env}= 5.24^{+0.30}_{-0.29}\\)%. GJ 1214 b remains a prime target for secondary eclipse observations of an enveloped terrestrial, the scheduling of which benefits from our tight constraint on the orbital eccentricity of \\(<0.063\\) at 95% confidence, which narrows the secondary eclipse window to 2.8 hours. By combining GJ 1214 with other mid-M dwarf transiting systems with intensive RV follow-up, we calculate the frequency of mid-M dwarf planetary systems with multiple small planets and find that \\(90^{+5}_{-21}\\)% of mid-M dwarfs with a known planet with mass \\(\\in [1,10] M_{\\oplus}\\) and orbital period \\(\\in [0.5,50]\\) days, will host at least one additional planet. We rule out additional planets around GJ 1214 down to \\(3 M_{\\oplus}\\) within 10 days such that GJ 1214 is a single-planet system within these limits, a result that has a \\(44^{+9}_{-5}\\)% probability given the prevalence of multi-planet systems around mid-M dwarfs. We also investigate mid-M dwarf RV systems and show that the probability that all reported RV planet candidates are real planets is \\(<12\\)% at 99% confidence, although this statistical argument is unable to identify the probable false positives.

Context: LHS 3844 b (TOI-136 b) is a ultra short-period, Earth-size exoplanet detected by TESS. It is one of the most favourable object for atmospheric characterisation and the study of its surface with the James Webb Space Telescope. However, the dynamical mass of this planet has not been measured yet. Aims: We aim to determine the mass of LHS 3844 b using high-precision radial velocity (RV) measurements and assess the robustness of the inferred signal across different noise and orbital modelling assumptions. Methods: We analyse 25 ESPRESSO RV observations within a fully Bayesian framework. We explore 15 competing RV models that differ in their treatment of correlated stellar variability (through different Gaussian Process kernels) and long-term drifts. Marginal likelihoods are computed for all models and used for Bayesian model comparison and evidence-weighted parameter estimation. Results: The RV planetary signal is robustly detected across all models, and the inferred semi-amplitude remains stable under all tested noise and drift prescriptions. From the evidence-weighted posterior samples we derive a planetary mass of \\(2.27 \\pm 0.23\\) M\\(_\\oplus\\) and a bulk density of \\(5.67 \\pm 0.65\\) gcm\\(^{-3}\\), consistent with a predominantly rocky composition. Model comparison favours GP kernels including periodic or quasi-periodic components associated with stellar rotation and disfavors models with additional long-term drifts. Using interior-structure inference, we find that the core mass fraction is comparable to (or slightly smaller than) Earth's and only trace amounts of water are permitted, supporting a dry, terrestrial interior. We also investigate a tentative additional signal near \\(\\sim 6.9\\) days, but Bayesian model comparison does not provide conclusive support for its planetary interpretation.

The nearby LHS 1678 (TOI-696) system contains two confirmed planets and a wide-orbit, likely-brown-dwarf companion, which orbit an M2 dwarf with a unique evolutionary history. The host star occupies a narrow \"gap\" in the HR diagram lower main sequence, associated with the M dwarf fully convective boundary and long-term luminosity fluctuations. This system is one of only about a dozen M dwarf multi-planet systems to date that hosts an ultra-short period planet (USP). Here we validate and characterize a third planet in the LHS 1678 system using TESS Cycle 1 and 3 data and a new ensemble of ground-based light curves. LHS 1678 d is a 0.98 +/-0.07 Earth radii planet in a 4.97-day orbit, with an insolation flux of 9.1 +0.9/-0.8 Earth insolations. These properties place it near 4:3 mean motion resonance with LHS 1678 c and in company with LHS 1678 c in the Venus zone. LHS 1678 c and d are also twins in size and predicted mass, making them a powerful duo for comparative exoplanet studies. LHS 1678 d joins its siblings as another compelling candidate for atmospheric measurements with the JWST and mass measurements using high-precision radial velocity techniques. Additionally, USP LHS 1678 b breaks the \"peas-in-a-pod\" trend in this system, although additional planets could fill in the \"pod\" beyond its orbit. LHS 1678's unique combination of system properties and their relative rarity among the ubiquity of compact multi-planet systems around M dwarfs makes the system a valuable benchmark for testing theories of planet formation and evolution.

We present a new algorithm for precision radial velocity (pRV) measurements, a line-by-line (LBL) approach designed to handle outlying spectral information in a simple but efficient manner. The effectiveness of the LBL method is demonstrated on two datasets, one obtained with SPIRou on Barnard's star, and the other with HARPS on Proxima Centauri. In the near-infrared, the LBL provides a framework for m/s-level accuracy in pRV measurements despite the challenges associated with telluric absorption and sky emission lines. We confirm with SPIRou measurements spanning 2.7 years that the candidate super-Earth on a 233-day orbit around Barnard's star is an artifact due to a combination of time-sampling and activity. The LBL analysis of the Proxima Centauri HARPS post-upgrade data alone easily recovers the Proxima b signal and also provides a 2-sigma detection of the recently confirmed 5-day Proxima d planet, but argues against the presence of the candidate Proxima c with a period of 1900 days. We provide evidence that the Proxima c signal is associated with small, unaccounted systematic effects affecting the HARPS-TERRA template matching RV extraction method for long-period signals. Finally, the LBL framework provides a very effective activity indicator, akin to the full width at half maximum derived from the cross-correlation function, from which we infer a rotation period of \\(92.1^+4.2_-3.5\\) days for Proxima.

The radius valley carries implications for how the atmospheres of small planets form and evolve, but this feature is visible only with highly precise characterizations of many small planets. We present the characterization of nine planets and one planet candidate with both NASA TESS and ESA CHEOPS observations, which adds to the overall population of planets bordering the radius valley. While four of our planets - TOI 118 b, TOI 455 b, TOI 560 b, and TOI 562 b - have already been published, we vet and validate transit signals as planetary using follow-up observations for five new TESS planets, including TOI 198 b, TOI 244 b, TOI 262 b, TOI 444 b, and TOI 470 b. While a three times increase in primary mirror size should mean that one CHEOPS transit yields an equivalent model uncertainty in transit depth as about nine TESS transits in the case that the star is equally as bright in both bands, we find that our CHEOPS transits typically yield uncertainties equivalent to between two and 12 TESS transits, averaging 5.9 equivalent transits. Therefore, we find that while our fits to CHEOPS transits provide overall lower uncertainties on transit depth and better precision relative to fits to TESS transits, our uncertainties for these fits do not always match expected predictions given photon-limited noise. We find no correlations between number of equivalent transits and any physical parameters, indicating that this behavior is not strictly systematic, but rather might be due to other factors such as in-transit gaps during CHEOPS visits or nonhomogeneous detrending of CHEOPS light curves.

GJ 367 is a bright (V \\(\\approx\\) 10.2) M1 V star that has been recently found to host a transiting ultra-short period sub-Earth on a 7.7 hr orbit. With the aim of improving the planetary mass and radius and unveiling the inner architecture of the system, we performed an intensive radial velocity follow-up campaign with the HARPS spectrograph -- collecting 371 high-precision measurements over a baseline of nearly 3 years -- and combined our Doppler measurements with new TESS observations from sectors 35 and 36. We found that GJ 367 b has a mass of \\(M_\\mathrm{b}\\) = 0.633 \\(\\pm\\) 0.050 M\\(_{\\oplus}\\) and a radius of \\(R_\\mathrm{b}\\) = 0.699 \\(\\pm\\) 0.024 R\\(_{\\oplus}\\), corresponding to precisions of 8% and 3.4%, respectively. This implies a planetary bulk density of \\(\\rho_\\mathrm{b}\\) = 10.2 \\(\\pm\\) 1.3 g cm\\(^{-3}\\), i.e., 85% higher than Earth's density. We revealed the presence of two additional non transiting low-mass companions with orbital periods of \\(\\sim\\)11.5 and 34 days and minimum masses of \\(M_\\mathrm{c}\\sin{i_\\mathrm{c}}\\) = 4.13 \\(\\pm\\) 0.36 M\\(_{\\oplus}\\) and \\(M_\\mathrm{d}\\sin{i_\\mathrm{d}}\\) = 6.03 \\(\\pm\\) 0.49 M\\(_{\\oplus}\\), respectively, which lie close to the 3:1 mean motion commensurability. GJ 367 b joins the small class of high-density planets, namely the class of super-Mercuries, being the densest ultra-short period small planet known to date. Thanks to our precise mass and radius estimates, we explored the potential internal composition and structure of GJ 367 b, and found that it is expected to have an iron core with a mass fraction of 0.91\\(^{+0.07}_{-0.23}\\). How this iron core is formed and how such a high density is reached is still not clear, and we discuss the possible pathways of formation of such a small ultra-dense planet.

K2-18 b is a transiting mini-Neptune that orbits a nearby (38 pc) cool M3 dwarf and is located inside its region of temperate irradiation. We report on the search for hydrogen escape from the atmosphere K2-18 b using Lyman-\\(\\) transit spectroscopy with the Space Telescope Imaging Spectrograph (STIS) instrument installed on the Hubble Space Telescope (HST). We analyzed the time-series of the fluxes of the stellar Lyman-\\(\\) emission of K2-18 in both its blue- and redshifted wings. We found that the average blueshifted emission of K2-18 decreases by \\(67\\% 18\\%\\) during the transit of the planet compared to the pre-transit emission, tentatively indicating the presence of H atoms escaping vigorously and being blown away by radiation pressure. This interpretation is not definitive because it relies on one partial transit. Based on the reconstructed Lyman-\\(\\) emission of K2-18, we estimate an EUV irradiation between \\(10^1-10^2\\) erg s\\(^-1\\) cm\\(^-2\\) and a total escape rate in the order of \\(10^8\\) g s\\(^-1\\). The inferred escape rate suggests that the planet will lose only a small fraction (< 1%) of its mass and retain its volatile-rich atmosphere during its lifetime. More observations are needed to rule out stellar variability effects, confirm the in-transit absorption and better assess the atmospheric escape and high-energy environment of K2-18 b.