[论文解读] Most Hot Jupiters Were Cool Giant Planets for More Than 1 Gyr

Stephen P. Schmidt, Kevin C. Schlaufman|arXiv (Cornell University)|Jan 20, 2026

Stellar, planetary, and galactic studies被引用 1

一句话总结

该论文使用标定的太阳邻域年龄-速度分散关系来比较三种热木星次人群，并推断在它们形成中存在显著的晚期高偏心迁移成分。

ABSTRACT

The origin of hot Jupiters is the oldest problem in exoplanet astrophysics. Hot Jupiters formed in situ or via disk migration should be in place just a few Myr after the formation of their host stars. On the other hand, hot Jupiters formed via eccentricity excitation and tidal damping as a result of planet--planet scattering or Kozai-Lidov oscillations may take 1 Gyr or more to arrive at their observed locations. We propose that the relative ages of hot Jupiters inside, near, and outside the bias-corrected peak of the observed hot Jupiter period distribution can be used to distinguish between these possibilities. Though the lack of precise and accurate age inferences for isolated hot Jupiter host stars makes this test difficult to implement, comparisons between the Galactic velocity dispersions of the hot Jupiter subpopulations enable this investigation. To transform relative age offsets into absolute age offsets, we calibrate the monotonically increasing solar neighborhood age--velocity dispersion relation using an all-sky sample of subgiants with precise ages and a metallicity distribution matched to that of hot Jupiter hosts. We find that the inside-peak and near-peak subpopulations are older than the outside-peak subpopulation, with the inside-peak subpopulation slightly older than the near-peak subpopulation. We conclude that at least 40\% but not more than 70\% of the hot Jupiter population must have formed via a late-time, peak-populating process like high-eccentricity migration that typically occurs more than 1.5 Gyr after system formation.

研究动机与目标

• Motivate the use of relative ages of hot Jupiters to distinguish formation scenarios (in situ/disk migration vs high-eccentricity migration).
• Calibrate a solar-neighborhood age–velocity dispersion relation using subgiants with precise ages to convert velocity dispersions into absolute ages.
• Divide hot Jupiters into inside-peak, near-peak, and outside-peak subsamples based on debiased orbital period peak.
• Compare characteristic mean ages of these subsamples to infer dominant formation channels over time.

提出的方法

• Assemble a sample of 503 hot Jupiters with P_orb < 10 d and 0.1 M_Jup < M_p < 10 M_Jup, excluding Kepler discoveries to avoid sampling biases.
• Use Gaia DR3 astrometry and APOGEE/ Gaia radial velocities to compute Galactic UVW velocities for host stars with quality cuts (parallax_over_error > 10, rv_nb_transits > 10, rv_expected_sig_to_noise > 5, ruwe < 1.4).
• Calibrate the solar-neighborhood age–velocity dispersion relation with metallicity-matched subgiants from Nataf et al. (2024) by constructing moving windows of 5000 stars, bootstrap resampling, and nonparametric smoothing.
• Divide hot Jupiters into inside-peak, near-peak, and outside-peak subpopulations using a debiased peak at P_orb = 3.92 d and period cuts 3.259 d and 4.545 d.
• Infer characteristic mean ages by locating overlaps of measured dispersions with the 1σ range of the metallicity-constrained age–velocity dispersion relation, without assuming a parametric age–dispersion form.

Figure 1: Cartoon of the characteristic mean ages expected for four different hot Jupiter formation scenarios: disk migration, disk migration plus tidal evolution, disk migration plus a late-time peak-populating mechanism, and disk migration plus a late-time peak-populating mechanism both affected b

实验结果

研究问题

• RQ1 What are the characteristic ages of hot Jupiters inside, near, and outside the debiased period peak after correcting for observational biases?
• RQ2 Do the relative ages of hot Jupiter subpopulations favor early-time formation (disk migration/in situ) or late-time formation (high-eccentricity migration) when tides are considered?
• RQ3 Can velocity-dispersion-based ages, calibrated in the solar neighborhood, meaningfully distinguish competing hot Jupiter formation pathways?
• RQ4 How does metallicity influence the calibration of the age–velocity dispersion relation for hot Jupiter hosts, and is its impact significant in the age inferences?
• RQ5 Is there evidence for a mixed formation history combining early- and late-time channels plus tidal evolution?

主要发现

• Inside-peak and near-peak subpopulations have characteristic mean ages around 3.1–3.3 Gyr, with inside-peak slightly older than near-peak.
• Outside-peak subpopulation has a younger characteristic mean age around 2.2–2.36 Gyr.
• The outside-peak subpopulation is ~0.75 Gyr younger than the other two, supporting a late-time peak-populating mechanism with subsequent tidal evolution.
• The results imply a mixed formation history: an early-time, uniformly-distributing mechanism plus a late-time, peak-populating mechanism, plus tidal evolution.
• Approximately 40% but not more than 70% of hot Jupiters must have formed via late-time high-eccentricity migration that typically occurs >1.5 Gyr after formation.
• Bias tests with synthetic samples and metallicity considerations indicate observed age differences are not due to observational biases in transit vs Doppler detections.

Figure 2: Solar neighborhood age–velocity dispersion relations as a function of metallicity. We subdivide the subgiant sample presented in Nataf et al. ( 2024 ) into four equal-size metallicity bins. We then order each subsample in age and calculate velocity dispersion in consecutive windows of 3000