We report on precise Doppler measurements of L231-32 (TOI-270), a nearby M dwarf (d = 22 pc, M⋆ = 0.39 M⊙, R⋆ = 0.38 R⊙), which hosts three transiting planets that were recently discovered using data from the Transiting Exoplanet Survey Satellite (TESS). The three planets are 1.2, 2.4, and 2.1 times the size of Earth and have orbital periods of 3.4, 5.7, and 11.4 days. We obtained 29 high-resolution optical spectra with the newly commissioned Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) and 58 spectra using the High Accuracy Radial velocity Planet Searcher (HARPS). From these observations, we find the masses of the planets to be 1.58 ± 0.26, 6.15 ± 0.37, and 4.78 ± 0.43 M⊕, respectively. The combination of radius and mass measurements suggests that the innermost planet has a rocky composition similar to that of Earth, while the outer two planets have lower densities. Thus, the inner planet and the outer planets are on opposite sides of the ‘radius valley’ — a region in the radius-period diagram with relatively few members, which has been interpreted as a consequence of atmospheric photo-evaporation. We place these findings into the context of other small close-in planets orbiting M dwarf stars, and use support vector machines to determine the location and slope of the M dwarf (Teff < 4000 K) radius valley as a function of orbital period. We compare the location of the M dwarf radius valley to the radius valley observed for FGK stars, and find that its location is a good match to photo-evaporation and core-powered mass loss models. Finally, we show that planets below the M dwarf radius valley have compositions consistent with stripped rocky cores, whereas most planets above have a lower density consistent with the presence of a H-He atmosphere.

We present an analysis of the first 20 second cadence light curves obtained by the TESS space telescope during its extended mission. We find improved precision of 20 second data compared to 2 minute data for bright stars when binned to the same cadence (≈10%–25% better for T ≲ 8 mag, reaching equal precision at T ≈ 13 mag), consistent with pre-flight expectations based on differences in cosmic-ray mitigation algorithms. We present two results enabled by this improvement. First, we use 20 second data to detect oscillations in three solar analogs (γ Pav, ζ Tuc, and π Men) and use asteroseismology to measure their radii, masses, densities, and ages to ≈1%, ≈3%, ≈1%, and ≈20% respectively, including systematic errors. Combining our asteroseismic ages with chromospheric activity measurements, we find evidence that the spread in the activity–age relation is linked to stellar mass and thus the depth of the convection zone. Second, we combine 20 second data and published radial velocities to recharacterize π Men c, which is now the closest transiting exoplanet for which detailed asteroseismology of the host star is possible. We show that π Men c is located at the upper edge of the planet radius valley for its orbital period, confirming that it has likely retained a volatile atmosphere and that the “asteroseismic radius valley” remains devoid of planets. Our analysis favors a low eccentricity for π Men c (<0.1 at 68% confidence), suggesting efficient tidal dissipation (Q/k 2,1 ≲ 2400) if it formed via high-eccentricity migration. Combined, these early results demonstrate the strong potential of TESS 20 second cadence data for stellar astrophysics and exoplanet science.

The characteristics of the radius valley, i.e. an observed lack of planets between 1.5-2 Earth radii at periods shorter than about 100 days, provide insights into the formation and evolution of close-in planets. We present a novel view of the radius valley by refitting the transits of 431 planets using Kepler 1-minute short cadence observations, the vast majority of which have not been previously analysed in this way. In some cases, the updated planetary parameters differ significantly from previous studies, resulting in a deeper radius valley than previously observed. This suggests that planets are likely to have a more homogeneous core composition at formation. Furthermore, using support-vector machines, we find that the radius valley location strongly depends on orbital period and stellar mass and weakly depends on stellar age, with $\partial \log {\left(R_{p, \text{valley}} \right)}/ \partial \log {P} = -0.096_{-0.027}^{+0.023}$, $\partial \log {\left(R_{p, \text{valley}} \right)}/ \partial \log {M_{\star }} = 0.231_{-0.064}^{+0.053}$, and $\partial \log {\left(R_{p, \text{valley}} \right)}/ \partial \log {\left( \text{age} \right)} = 0.033_{-0.025}^{+0.017}$. These findings favour thermally-driven mass loss models such as photoevaporation and core-powered mass loss, with a slight preference for the latter scenario. Finally, this work highlights the value of transit observations with short photometric cadence to precisely determine planet radii, and we provide an updated list of precisely and homogeneously determined parameters for the planets in our sample.

We report photometric follow-up observations of thirteen exoplanets (HATS-1 b, HATS-2 b, HATS-3 b, HAT-P-18 b, HAT-P-27 b, HAT-P-30 b, HAT-P-55 b, KELT-4A b, WASP-25 b, WASP-42 b, WASP-57 b, WASP-61 b and WASP-123 b), as part of the Original Research By Young Twinkle Students (ORBYTS) programme. All these planets are potentially viable targets for atmospheric characterisation and our data, which were taken using the LCOGT network of ground-based telescopes, will be combined with observations from other users of ExoClock to ensure that the transit times of these planets continue to be well-known, far into the future.

We investigate the effect of observing cadence on the precision of radius ratio values obtained from transit light curves by performing uniform Markov Chain Monte Carlo fits of 46 exoplanets observed by the Transiting Exoplanet Survey Satellite (TESS) in multiple cadences. We find median improvements of almost 50% when comparing fits to 20s and 120s cadence light curves to 1800s cadence light curves, and of 37% when comparing 600s cadence to 1800s cadence. Such improvements in radius precision are important, for example, to precisely constrain the properties of the radius valley or to characterize exoplanet atmospheres. We also implement a numerical Information Analysis to predict the precision of parameter estimates for different observing cadences. We tested this analysis on our sample and found it reliably predicts the effect of shortening observing cadence with errors in the predicted % precision of $\lesssim 0.5 \%$ for most cases. We apply this method to 157 TESS object of interest that have only been observed with 1800s cadence to predict the precision improvement that could be obtained by reobservations with shorter cadences and provide the full table of expected improvements. We report the 10 planet candidates that would benefit the most from reobservations at short cadence. Our implementation of the Information Analysis for the prediction of the precision of exoplanet parameters, Prediction of Exoplanet Precisions using Information in Transit Analysis (PEPITA) is made publicly available.