Madyson G. Barber

Young planets (R _⊕ planet on a 10.47 day orbit, and report the candidate TIC 150070085 c, a 3.0 R _⊕ planet on a 15.90 day orbit. While we are unable to validate the second signal, the proximity to mean-motion resonance (3:2) and transit timing variations observed in the transits of TIC 150070085 b strongly suggest that the signal is planetary. We confirm the host star as a member of Alessi 84 and combine the group’s color–magnitude diagram, rotation, and variability properties to update the age to 135 ± 10 Myr. We additionally use MAROON-X to observe the Rossiter–McLaughlin signal of TIC 150070085 b and measure the sky projected obliquity angle ( λ ). We find that TIC 150070085 b is consistent with a near-aligned orbit with its host star (∣ λ ∣ = 18° ± 12°), in line with similarly aged transiting planets with measured λ values. Continued discovery and characterization of planets in this age regime are vital to link planetary infancy (1 Gyr).

The close-in small planet population may be formed either with hydrogen/helium-dominated envelopes or with water-rich interiors. Both scenarios reproduce the present-day planet population in mass, radius, and periods, and are difficult to differentiate with the mature planet demographic. Hydrogen/helium “gas dwarfs” have low mean-molecular-weight atmospheres, while “water worlds” have envelopes that are significantly heavier, and as such, these two scenarios have different evolution tracks that diverge in the first ≈50 Myr of their evolution. We show that a low Earth orbit multiband photometric survey mission, within the scope of the National Aeronautics and Space Administration Small Explorers Program, can determine the frequency of young close-in planets at the 5% level and definitively differentiate between the competing “gas-dwarf” and “water-world” hypotheses. We simulate a 2.5 yr mission capable of simultaneous multiband near-ultraviolet, optical, and near-infrared wide field photometry. Such a mission would perform a photometric survey of 30 different star fields selected to probe the young star population. The mission will yield ≈100 transiting planets in young star clusters and associations with ages <50 Myr. In comparison, only 20 such planets are known from K2 and TESS today.

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 infant (R _⊕ planet on a 14.8-day orbit. TOI-6448 was previously identified to be a likely member of Vela Population IV. We confirm the star’s membership and rederive the age of the cluster using isochrones, variability, and gyrochronology. We find the star, and thus planet, to be 34 ± 3 Myr. Like other young planets, TOI-6448 b lands in a region of parameter space with few older planets. While just one data point, this fits with prior findings of an excess of 5–11 R _⊕ planets around young stars far beyond what can be explained by reduced sensitivity at young ages. Our ongoing searches of Vela, Taurus-Auriga, Sco-Cen, and Orion are expected to reveal dozens more <50 Myr transiting 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.

Despite the wide range of planet–star (mis)alignments in the mature population of transiting exoplanets, the small number of known young transiting planets are nearly all aligned with the rotation axes of their host stars, as determined by the sky-projected obliquity angle. The small number of young systems with measured obliquities limits statistical conclusions. Here we determine the sky-projected obliquity ( λ ) of the 3 Myr transiting planet with a misaligned outer protoplanetary disk, TIDYE-1 b (IRAS 04125+2902b), using the Rossiter–McLaughlin (RM) effect. Our dataset lacks a pretransit baseline and ingress, complicating a blind RM fit. Instead, we use contemporaneous spectra and photometry from a mass-measurement campaign to model the stellar activity trend across the transit and provide an external prior on the velocity baseline. We determine ∣ λ ∣ = 11 . 8 − 5.0 + 5.9 ° . Combined with the published rotational velocity of the star, we find a true three-dimensional obliquity of ψ = 15 . 2 − 5.7 + 7.3 ° . Our result is consistent with an aligned orbit, suggesting the planet remains aligned to its star even though the outer disk is misaligned, though additional RM observations are needed to exclude the low-probability tail of misaligned (>30°) scenarios present in our posterior.

Gaps in the exoplanet population, such as the Neptunian Desert, point to the importance of mass loss in sculpting the radii of close-in exoplanets. Young planets (α transit in high-resolution spectra of three young planets, HD 63433 b (400 Myr), DS Tuc A b (45 Myr), and HIP 67522 b (17 Myr) using HARPS-N, Magellan-PFS, and CHIRON, respectively. We validate our method by testing it on several photospheric lines less impacted by stellar variability. We find no evidence of a transit signal for HD 63433 b and DS Tuc A b (3 σ limits of 0.9% and 0.3%, respectively). For HIP 67522 b, we detect significant excess absorption (3.44% ± 0.28%) aligned with the transit time, narrow compared to the stellar line, and blueshifted from the stellar rest frame. In combination, these suggest the signal is from the planet. However, stellar variation in the H α line over the course of the observations is comparable in size to the transit signature and the duration is shorter than the photometric transit, so this detection requires confirmation. Our findings, and other recent results in the literature, suggest that planets younger than 50 Myr are more favorable for the detection of atmospheric escape with H α observations, though older populations might still show escape in other diagnostics.

The discovery of infant (< 50 Myr), close-in (<30-day period) planets is vital in understanding the formation mechanisms that lead to the distribution of mature transiting planets as discovered by Kepler. Despite several discoveries in this age bin, the sample is still too small for a robust statistical comparison to older planets. Here we report the validation of TOI-6448 b, an 8.8 +/- 0.8 Re planet on a 14.8 day orbit. TOI-6448 was previously identified to be a likely member of Vela Population IV. We confirm the star's membership and re-derive the age of the cluster using isochrones, variability, and gyrochronology. We find the star, and thus planet, to be 34 +/- 3 Myr. Like other young planets, TOI-6448 b lands in a region of parameter space with few older planets. While just one data point, this fits with prior findings of an excess of 5-11Re planets around young stars far beyond what can be explained by reduced sensitivity at young ages. Our ongoing search of Vela, Taurus-Auriga, Sco-Cen, and Orion are expected to reveal dozens more < 50 Myr transiting planets.