The orbital distribution of giant planets is crucial for understanding how terrestrial planets form and predicting yields of exoplanet surveys. Here, we derive giant planets occurrence rates as a ...function of orbital period by taking into account the detection efficiency of the Kepler and radial velocity (RV) surveys. The giant planet occurrence rates for Kepler and RV show the same rising trend with increasing distance from the star. We identify a break in the RV giant planet distribution between ∼2 and 3 au-close to the location of the snow line in the solar system-after which the occurrence rate decreases with distance from the star. Extrapolating a broken power-law distribution to larger semimajor axes, we find good agreement with the ∼1% planet occurrence rates from direct imaging surveys. Assuming a symmetric power law, we also estimate that the occurrence of giant planets between 0.1 and 100 au is for planets with masses 0.1-20 MJ and decreases to for planets more massive than Jupiter. This implies that only a fraction of the structures detected in disks around young stars can be attributed to giant planets. Various planet population synthesis models show good agreement with the observed distribution, and we show how a quantitative comparison between model and data can be used to constrain planet formation and migration mechanisms.
Abstract
Planets are born from disks of gas and dust, and observations of protoplanetary disks are used to constrain the initial conditions of planet formation. However, dust mass measurements of ...Class II disks with ALMA have called into question whether they contain enough solids to build the exoplanets that have been detected to date. In this paper, we calculate the mass and spatial scale of solid material around Sun-like stars probed by transit and radial velocity exoplanet surveys and compare those to the observed dust masses and sizes of Class II disks in the same stellar-mass regime. We show that the apparent mass discrepancy disappears when accounting for observational selection and detection biases. We find a discrepancy only when the planet formation efficiency is below 100%, or if there is a population of undetected exoplanets that significantly contributes to the mass in solids. We identify a positive correlation between the masses of planetary systems and their respective orbital periods, which is consistent with the trend between the masses and the outer radii of Class II dust disks. This implies that, despite a factor 100 difference in spatial scale, the properties of protoplanetary disks seem to be imprinted on the exoplanet population.
Abstract
We analyze the CORALIE/HARPS sample of exoplanets found by the Doppler radial-velocity method for signs of the predicted gap or “desert” at 10–100
M
⊕
caused by runaway gas accretion at ...semimajor axes of <3 au. We find that these data are not consistent with this prediction. This result is similar to the finding by the MOA gravitational microlensing survey that found no desert in the exoplanet distribution for exoplanets in slightly longer period orbits and somewhat lower host masses (Suzuki et al. 2018). Together, these results imply that the runaway gas accretion scenario of the core accretion theory does not have a large influence on the final mass and semimajor axis distribution of exoplanets.
Abstract
We explore atmospheric escape from close-in exoplanets with the highest mass-loss rates. First, we locate the transition from stellar X-ray and UV-driven escape to rapid Roche lobe overflow, ...which occurs once the 10–100 nbar pressure level in the atmosphere reaches the Roche lobe. Planets enter this regime when the ratio of the substellar radius to the polar radius along the visible surface pressure level, which aligns with a surface of constant Roche potential, is X/Z ≳ 1.2 for Jovian planets (
M
p ≳ 100
M
⊕
) and X/Z ≳ 1.02 for sub-Jovian planets (
M
p
≈ 10–100
M
⊕
). Around a Sun-like star, this regime applies to orbital periods of less than two days for planets with radii of about 3–14R
⊕
. Our results agree with the properties of known transiting planets and can explain parts of the sub-Jovian desert in the population of known exoplanets. Second, we present detailed numerical simulations of atmospheric escape from a planet like Uranus or Neptune orbiting close to a Sun-like star that support the results above and point to interesting qualitative differences between hot Jupiters and sub-Jovian planets. We find that hot Neptunes with solar-metallicity hydrogen and helium envelopes have relatively more extended upper atmospheres than typical hot Jupiters, with a lower ionization fraction and higher abundances of escaping molecules. This is consistent with existing ultraviolet transit observations of warm Neptunes, and it might provide a way to use future observations and models to distinguish solar-metallicity atmospheres from higher-metallicity atmospheres.
Abstract
Reliable detections of Earth-sized planets in the habitable zone remain elusive in the Kepler sample, even for M dwarfs. The Kepler sample was once thought to contain a considerable number ...of M-dwarf stars (
T
eff
< 4000 K), which hosted enough Earth-sized (0.5, 1.5
R
⊕
) planets to estimate their occurrence rate (
η
⊕
) in the habitable zone. However, updated stellar properties from Gaia have shifted many Kepler stars to earlier spectral type classifications, with most stars (and their planets) now measured to be larger and hotter than previously believed. Today, only one partially reliable Earth-sized candidate remains in the optimistic habitable zone, and zero in the conservative zone. Here we performed a new investigation of Kepler's Earth-sized planets orbiting M-dwarf stars, using occurrence rate models with considerations of updated parameters and candidate reliability. Extrapolating our models to low instellations, we found an occurrence rate of
η
⊕
=
8.58
−
8.22
+
17.94
%
for the conservative habitable zone (and
14.22
−
12.71
+
24.96
%
for the optimistic one), consistent with previous works when considering the large uncertainties. Comparing these estimates to those from similarly comprehensive studies of Sun-like stars, we found that the current Kepler sample does not offer evidence to support an increase in
η
⊕
from FGK to M stars. While the Kepler sample is too sparse to resolve an occurrence trend between early and mid- to late M dwarfs for Earth-sized planets, studies including larger planets and/or data from the K2 and TESS missions are well suited to this task.
Abstract
The NASA K2 mission obtained high-precision time-series photometry for four young clusters, including the near-twin 600–800 Myr old Praesepe and Hyades clusters. Hot sub-Neptunes are highly ...prone to mass-loss mechanisms, given their proximity to the host star and the weakly bound gaseous envelopes, and analyzing this population at young ages can provide strong constraints on planetary evolution models. Using our automated transit detection pipeline, we recover 15 planet candidates across the two clusters, including 10 previously confirmed planets. We find a hot sub-Neptune occurrence rate of 79%–107% for GKM stars in the Praesepe cluster. This is 2.5–3.5
σ
higher than the occurrence rate of
16.54
−
0.98
+
1.00
% for the same planets orbiting the ∼3–9 Gyr old GKM field stars observed by K2, even after accounting for the slightly supersolar metallicity (Fe/H ∼ 0.2 dex) of the Praesepe cluster. We examine the effect of adding ∼100 targets from the Hyades cluster and extending the planet parameter space under examination, and we find similarly high occurrence rates in both cases. The high occurrence rate of young, hot sub-Neptunes could indicate either that these planets are undergoing atmospheric evolution as they age, or that planetary systems that formed when the Galaxy was much younger are substantially different than from today. Under the assumption of the atmospheric mass-loss scenario, a significantly higher occurrence rate of these planets at the intermediate ages of Praesepe and Hyades appears more consistent with the core-powered mass-loss scenario for the origin of the planet radius valley, compared to the photoevaporation scenario.
We present ALMA 0.87 mm continuum, HCO+ J = 4-3 emission line, and CO J = 3-2 emission line data of the disk of material around the young, Sun-like star PDS 70. These data reveal the existence of a ...possible two-component transitional disk system with a radial dust gap of 0 42 0 05, an azimuthal gap in the HCO+ J = 4-3 moment zero map, as well as two bridge-like features in the gas data. Interestingly these features in the gas disk have no analog in the dust disk making them of particular interest. We modeled the dust disk using the Monte Carlo radiative transfer code HOCHUNK3D using a two-disk component. We find that there is a radial gap that extends from 15 to 60 au in all grain sizes, which differs from previous work.
Abstract
The demographics of young exoplanets can shed light on their formation and evolution processes. Exoplanet properties are derived from the properties of their host stars. As such, it is ...important to accurately characterize the host stars since any systematic biases in their derivation can negatively impact the derivation of planetary properties. Here we present a uniform catalog of photometrically derived stellar effective temperatures, luminosities, radii, and masses for 4865 young (<1 Gyr) stars in 31 nearby clusters and moving groups within 200 pc. We compared our photometrically derived properties to a subset of those derived from spectra and found them to be in good agreement. We also investigated the effect of stellar properties on the detection efficiency of transiting short-period young planets with TESS as calculated in Fernandes et al. (2022) and found an overall increase in the detection efficiency when the new photometrically derived properties were taken into account. Most notably, there is a 1.5 × increase in the detection efficiencies for sub-Neptunes/Neptunes (1.8–6
R
⊕
) implying that, for our sample of young stars, better characterization of host star properties can lead to the recovery of more small transiting planets. Our homogeneously derived catalog of updated stellar properties, along with a larger unbiased stellar sample and more detections of young planets, will be a crucial input to the accurate estimation of the occurrence rates of young short-period planets.
Abstract
In this study, we performed a homogeneous analysis of the planets around FGK dwarf stars observed by the Kepler and K2 missions, providing spectroscopic parameters for 310 K2 targets ...—including 239 Scaling K2 hosts—observed with Keck/HIRES. For orbital periods less than 40 days, we found that the distribution of planets as a function of orbital period, stellar effective temperature, and metallicity was consistent between K2 and Kepler, reflecting consistent planet formation efficiency across numerous ∼1 kpc sight-lines in the local Milky Way. Additionally, we detected a 3× excess of sub-Saturns relative to warm Jupiters beyond 10 days, suggesting a closer association between sub-Saturn and sub-Neptune formation than between sub-Saturn and Jovian formation. Performing a joint analysis of Kepler and K2 demographics, we observed diminishing super-Earth, sub-Neptune, and sub-Saturn populations at higher stellar effective temperatures, implying an inverse relationship between formation and disk mass. In contrast, no apparent host-star spectral-type dependence was identified for our population of Jupiters, which indicates gas-giant formation saturates within the FGK mass regimes. We present support for stellar metallicity trends reported by previous Kepler analyses. Using Gaia DR3 proper motion and radial velocity measurements, we discovered a galactic location trend; stars that make large vertical excursions from the plane of the Milky Way host fewer super-Earths and sub-Neptunes. While oscillation amplitude is associated with metallicity, metallicity alone cannot explain the observed trend, demonstrating that galactic influences are imprinted on the planet population. Overall, our results provide new insights into the distribution of planets around FGK dwarf stars and the factors that influence their formation and evolution.
Abstract
Understanding the occurrence of Earth-sized planets in the habitable zone of Sun-like stars is essential to the search for Earth analogs. Yet a lack of reliable Kepler detections for such ...planets has forced many estimates to be derived from the close-in (2 <
P
orb
< 100 days) population, whose radii may have evolved differently under the effect of atmospheric mass-loss mechanisms. In this work, we compute the intrinsic occurrence rates of close-in super-Earths (∼1–2
R
⊕
) and sub-Neptunes (∼2–3.5
R
⊕
) for FGK stars (0.56–1.63
M
⊙
) as a function of orbital period and find evidence of two regimes: where super-Earths are more abundant at short orbital periods, and where sub-Neptunes are more abundant at longer orbital periods. We fit a parametric model in five equally populated stellar mass bins and find that the orbital period of transition between these two regimes scales with stellar mass, like
P
trans
∝
M
*
1.7
±
0.2
. These results suggest a population of former sub-Neptunes contaminating the population of gigayear-old close-in super-Earths, indicative of a population shaped by atmospheric loss. Using our model to constrain the long-period population of intrinsically rocky planets, we estimate an occurrence rate of
Γ
⊕
=
15
−
4
+
6
%
for Earth-sized habitable zone planets, and predict that sub-Neptunes may be ∼ twice as common as super-Earths in the habitable zone (when normalized over the natural log-orbital period and radius range used). Finally, we discuss our results in the context of future missions searching for habitable zone planets.
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