Pa Chia Thao

The discovery of young (4 σ ), although differences in methodology make a totally fair comparison challenging. We show that spots have a weak-to-negligible impact on our results, and similarly cannot explain the higher TTV fraction. Longer-term monitoring will be required to validate these TTVs as planetary in nature and confirm the high TTV rate. While the candidate TTV signals detected here are sparsely sampled, our work provides a clear priority list for additional ground-based observations, and for multiplanet TTVs, to measure the masses and eccentricities of these planets.

The discovery of young ( 4$σ$), although differences in methodology make a totally fair comparison challenging. We show that spots have a weak-to-negligible impact on our results, and similarly cannot explain the higher TTV fraction. Longer-term monitoring will be required to validate these TTVs as planetary in nature and confirm the high TTV rate. While the candidate TTV signals detected here are sparsely sampled, our work provides a clear priority list for additional ground-based observations, and for multi-planet TTVs, attempt to measure the masses and eccentricities of these planets.

Our brains are hardwired for pattern recognition as correlations are useful for predicting and understanding nature. As more exoplanet atmospheres are being characterized with JWST, we are starting to unveil their properties on a population level. Here we present a framework for comparing exoplanet transmission spectroscopy from 3 to 5 μm with four bands: L (2.9–3.7 μm), SO₂ (3.95–4.1 μm), CO₂ (4.25–4.4 μm), and CO (4.5–4.9 μm). Together, the four bands cover the major carbon-, oxygen-, nitrogen-, and sulfur-bearing molecules including H₂O, CH₄, NH₃, H₂S, SO₂, CO₂, and CO. Among the eight high-precision gas giant exoplanet planet spectra we collect, we find strong correlations between the SO₂ – L index and planet mass (r = −0.41 ± 0.09) and temperature (r = −0.64 ± 0.08), indicating SO₂ preferably exists (SO₂ – L > −0.5) among low-mass (∼ M _J) and cooler (∼ 2 – L and CO – L indices. Under equilibrium chemistry and isothermal thermal structure assumptions, we find that the planet sample favors supersolar metallicity and a low C/O ratio (2 – L versus CO₂ – L diagram, similar to the color–magnitude diagram for stars and brown dwarfs. All reported trends here will be testable and will be further quantified with existing and future JWST observations within the next few years.

The characterization of young planets (μm transmission spectrum of the 17 Myr, Jupiter-size (R ∼10R _⊕) planet, HIP 67522b, observed with JWST NIRSpec/G395H. To check for spot contamination, we obtain a simultaneous g-band transit with the Southern Astrophysical Research Telescope. The spectrum exhibits absorption features 30%–50% deeper than the overall depth, far larger than expected from an equivalent mature planet, and suggests that HIP 67522b’s mass is M _⊕ irrespective of cloud cover and stellar contamination. A Bayesian retrieval analysis returns a mass constraint of 13.8 ± 1.0 M _⊕. This challenges the previous classification of HIP 67522b as a hot Jupiter and instead, positions it as a precursor to the more common sub-Neptunes. With a density of −3, HIP 67522 b is one of the lowest-density planets known. We find strong absorption from H₂O and CO₂ (≥7σ), a modest detection of CO (3.5σ), and weak detections of H₂S and SO₂ (≃2σ). Comparisons with radiative-convective equilibrium models suggest supersolar atmospheric metallicities and solar-to-subsolar C/O ratios, with photochemistry further constraining the inferred atmospheric metallicity to 3 × 10 solar due to the amplitude of the SO₂ feature. These results point to the formation of HIP 67522b beyond the water snowline, where its envelope was polluted by icy pebbles and planetesimals. The planet is likely experiencing substantial mass loss (0.01–0.03 M _⊕ Myr⁻¹), sufficient for envelope destruction within a gigayear. This highlights the dramatic evolution occurring within the first 100 Myr of its existence.

The youngest (R _⊕) planet on a tight orbit. In their discovery paper, Rizzuto et al. reported a tentative single-transit detection of an additional planet in the system using TESS. Here, we report the discovery of HIP 67522c, a 7.9 R _⊕ planet that matches with that single-transit event. We confirm the signal with ground-based multiwavelength photometry from Sinistro and MuSCAT4. At a period of 14.33 days, planet c is close to a 2:1 mean-motion resonance with b (6.96 days or 2.06:1). The light curve shows distortions during many of the transits, which are consistent with spot-crossing events and/or flares. Fewer stellar activity events are seen in the transits of planet b, suggesting that planet c is crossing a more active latitude. Such distortions, combined with systematics in the TESS light-curve extraction, likely explain why planet c was previously missed.

Small planets (R _p ≤ 4 R _⊕) are divided into rocky super-Earths and gaseous sub-Neptunes separated by a radius gap, but the mechanisms that produce these distinct planet populations remain unclear. Binary stars are the only main-sequence systems with an observable record of the protoplanetary disk lifetime and mass reservoir, and the demographics of planets in binaries may provide insights into planet formation and evolution. To investigate the radius distribution of planets in binary star systems, we observed 207 binary systems hosting 283 confirmed and candidate transiting planets detected by the Kepler mission, then recharacterized the planets while accounting for the observational biases introduced by the secondary star. We found that the population of planets in close binaries (ρ ≤ 100 au) is significantly different from the planet population in wider binaries (ρ > 300 au) or single stars. In contrast to planets around single stars, planets in close binaries appear to have a unimodal radius distribution with a peak near the expected super-Earth peak of R _p ∼ 1.3 R _⊕ and a suppressed population of sub-Neptunes. We conclude that we are observing the direct impact of a reduced disk lifetime, smaller mass reservoir, and possible altered distribution of solids reducing the sub-Neptune formation efficiency. Our results demonstrate the power of binary stars as a laboratory for exploring planet formation and as a controlled experiment of the impact of varied initial conditions on mature planet populations.

Young (R _⊕ and 2.88 ± 0.10 R _⊕ and orbit their host star every 4.18 and 17.95 days, respectively. With their bright (K = 9.1 mag), small (R _* = 0.44 R _⊙), and cool (T _eff = 3326 K) host star, these planets represent excellent candidates for atmospheric characterization with JWST.

The dispersed remnants of stellar nurseries, stellar associations, provide unparalleled samples of coeval stars critical for studies of stellar and planetary formation and evolution. The Carina Stellar Association is one of the closest stellar associations to Earth, and yet measurements of its age have varied from 13 to 45 Myr. We aim to update the age of Carina using the lithium depletion boundary (LDB) method. We obtain new measurements of the Li 6708 Å absorption feature in likely members using optical spectra from the Goodman High Throughput Spectrograph on SOAR and NRES on LCO. We detect the depletion boundary at M _K ≃ 6.8 (M5). This age is consistent within uncertainties across six different models, including those that account for magnetic fields and spots. We also estimate the age through analysis of the group’s overall variability, and by comparing the association members’ color–magnitude diagram to stellar evolutionary models using a Gaussian Mixture Model, recovering ages consistent with the LDB. Combining these age measures we obtain an age for the Carina association of 41 − 5 + 3 Myr. The resulting age agrees with the older end of previous age measurements and is consistent with the lithium depletion age for the neighboring Tucana-Horologium moving group.

The dispersed remnants of stellar nurseries, stellar associations provide unparalleled samples of coeval stars critical for studies of stellar and planetary formation and evolution. The Carina Stellar Association is one of the closest stellar associations to Earth, and yet measurements of its age have varied from 13 to 45 Myr. We aim to update the age of Carina using the Lithium Depletion Boundary method. We obtain new measurements of the Li 6708 Angstrom, absorption feature in likely members using optical spectra from the Goodman HTS on SOAR and NRES on LCO. We detect the depletion boundary at M_K ~= 6.8 (M5), which corresponds to an age of 41(+3,-5) Myr. The age is consistent within uncertainties across six different models, including those that account for magnetic fields and spots. We also estimate the age through analysis of the group's overall variability, and by comparing the association members' CMD to stellar evolutionary models using a Gaussian Mixture Model, recovering ages consistent with the LDB. The resulting age agrees with the older end of previous age measurements and is consistent with the lithium depletion age for the neighboring Tucana-Horologium Moving Group.