We present TRICERATOPS, a new Bayesian tool that can be used to vet and validate TESS Objects of Interest (TOIs). We test the tool on 68 TOIs that have been previously confirmed as planets or rejected as astrophysical false positives. By looking in the false-positive probability (FPP)−nearby false-positive probability (NFPP) plane, we define criteria that TOIs must meet to be classified as validated planets (FPP < 0.015 and NFPP < 10−3), likely planets (FPP < 0.5 and NFPP < 10−3), and likely nearby false positives (NFPP > 10−1). We apply this procedure on 384 unclassified TOIs and statistically validate 12, classify 125 as likely planets, and classify 52 as likely nearby false positives. Of the 12 statistically validated planets, 9 are newly validated. TRICERATOPS is currently the only TESS vetting and validation tool that models transits from nearby contaminant stars in addition to the target star. We therefore encourage use of this tool to prioritize follow-up observations that confirm bona fide planets and identify false positives originating from nearby stars.

Data from the newly-commissioned Transiting Exoplanet Survey Satellite (TESS) has revealed a "hot Earth" around LHS 3844, an M dwarf located 15 pc away. The planet has a radius of 1.32 ± 0.02 R ⊕ and orbits the star every 11 hours. Although the existence of an atmosphere around such a strongly irradiated planet is questionable, the star is bright enough (I = 11.9, K = 9.1) for this possibility to be investigated with transit and occultation spectroscopy. The star's brightness and the planet's short period will also facilitate the measurement of the planet's mass through Doppler spectroscopy.

Bean et al.

Transmission spectroscopy 1,2,3 of exoplanets has revealed signatures of water vapor, aerosols, and alkali metals in a few dozen exoplanet atmospheres 4,5 . However, these previous inferences with the Hubble and Spitzer Space Telescopes were hindered by the observations' relatively narrow wavelength range and spectral resolving power, which precluded the unambiguous identification of other chemical species -in particular the primary carbon-bearing molecules 6,7 . Here we report a broad-wavelength 0.5-5.5 µm atmospheric transmission spectrum of WASP39 b 8 , a 1200 K, roughly Saturn-mass, Jupiter-radius exoplanet, measured with JWST NIRSpec's PRISM mode 9 as part of the JWST Transiting Exoplanet Community Early Release Science Team program 10,11,12 . We robustly detect multiple chemical species at high significance, including Na (19σ), H 2 O (33σ), CO 2 (28σ), and CO (7σ). The non-detection of CH 4 , combined with a strong CO 2 feature, favours atmospheric models with a super-solar atmospheric metallicity. An unanticipated absorption feature at 4µm is best explained by SO 2 (2.7σ), which could be a tracer of atmospheric photochemistry. These observations demonstrate JWST's sensitivity to a rich diversity of exoplanet compositions and chemical processes.We observed one transit of WASP-39b on 10 July 2022 with JWST's Near InfraRed Spectrograph (NIRSpec) 9,13 , using the PRISM mode, as part of the JWST Transiting Exoplanet Community Early Release Science Program (ERS Program 1366) (PIs: N. Batalha, J. Bean, K. Stevenson) 10,11 . These observations cover the 0.5-5.5µm wavelength range at a native resolving power of R = λ/∆λ ∼ 20-300. WASP-39b was selected for this JWST ERS Program due to previous space-and ground-based observations revealing strong alkali metal absorption and multiple prominent H 2 O bands 4,6,14,15,16 , suggesting strong signal-to-noise could be obtained with JWST. However, the limited wavelength range of existing transmission spectra (0.3-1.65µm, combined with two wide photometric Spitzer channels at 3.6 and 4.5µm) left several important questions unresolved. Previous estimates of WASP-39b's atmospheric metallicity-a measure of the relative abundance of all gases heavier than hydrogen or helium-vary by four orders of magnitude 6,16,17,18,19,20 . Accurate determinations of metallicity can elucidate formation pathways and provide greater insight into the planet's history 21 . The JWST NIRSpec PRISM observations we present here offer a more detailed view into WASP-39b's atmospheric composition than has previously been possible (see ref. 21 for an initial infrared analysis of this data).We obtained time-series spectroscopy over 8.23 hours centered around the transit event to extract the wavelength-dependent absorption by the planet's atmosphere-i.e., the transmission spectrum, which probes the planet's day-night terminator region near millibar pressures. We used NIRSpec PRISM in Bright Object Time Series (BOTS) mode. WASP-39 is a bright, nearby, relatively inactive 23 G7 type star with an effective tempe...

The Saturn-mass exoplanet WASP-39b has been the subject of extensive efforts to determine its atmospheric properties using transmission spectroscopy1–4. However, these efforts have been hampered by modelling degeneracies between composition and cloud properties that are caused by limited data quality5–9. Here we present the transmission spectrum of WASP-39b obtained using the Single-Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST. This spectrum spans 0.6–2.8 μm in wavelength and shows several water-absorption bands, the potassium resonance doublet and signatures of clouds. The precision and broad wavelength coverage of NIRISS/SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favouring a heavy-element enhancement (‘metallicity’) of about 10–30 times the solar value, a sub-solar carbon-to-oxygen (C/O) ratio and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are also best explained by wavelength-dependent, non-grey clouds with inhomogeneous coverageof the planet’s terminator.