Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504

TL;DR

This paper reports the direct imaging discovery of a cold, low-mass Jovian exoplanet around a Sun-like star, GJ 504, providing new insights into planetary atmospheres and formation mechanisms at an older system age.

Contribution

It presents the first direct imaging of a cold, low-mass exoplanet around an older star, with properties distinct from previously imaged planets, aiding understanding of planetary atmospheres and formation.

Findings

Estimated mass of 4 (+4.5, -1.0) Jupiter masses.

Projected separation of 43.5 AU exceeds core accretion predictions.

Cooler temperature (510 K) and bluer color indicating a cloud-free atmosphere.

Abstract

Several exoplanets have recently been imaged at wide separations of >10 AU from their parent stars. These span a limited range of ages (<50 Myr) and atmospheric properties, with temperatures of 800--1800 K and very red colors (J - H > 0.5 mag), implying thick cloud covers. Furthermore, substantial model uncertainties exist at these young ages due to the unknown initial conditions at formation, which can lead to an order of magnitude of uncertainty in the modeled planet mass. Here, we report the direct imaging discovery of a Jovian exoplanet around the Sun-like star GJ 504, detected as part of the SEEDS survey. The system is older than all other known directly-imaged planets; as a result, its estimated mass remains in the planetary regime independent of uncertainties related to choices of initial conditions in the exoplanet modeling. Using the most common exoplanet cooling model, and given the system age of 160 [+350, -60] Myr, GJ 504 b has an estimated mass of 4 [+4.5, -1.0] Jupiter masses, among the lowest of directly imaged planets. Its projected separation of 43.5 AU exceeds the typical outer boundary of ~30 AU predicted for the core accretion mechanism. GJ 504 b is also significantly cooler (510 [+30, -20] K) and has a bluer color (J-H = -0.23 mag) than previously imaged exoplanets, suggesting a largely cloud-free atmosphere accessible to spectroscopic characterization. Thus, it has the potential of providing novel insights into the origins of giant planets, as well as their atmospheric properties.