Radial-velocity discovery of a second planet in the TOI-1338/BEBOP-1 circumbinary system

TL;DR

This paper reports the first radial-velocity detection of a circumbinary planet, TOI-1338/BEBOP-1c, around an eclipsing binary system, marking a significant advancement in exoplanet discovery methods and system characterization.

Contribution

It presents the first radial-velocity discovery of a circumbinary planet and confirms only the second multiplanet circumbinary system to date.

Findings

Discovered a 65.2 Earth-mass circumbinary planet with a 215.5-day period.

Placed an upper mass limit of 21.8 Earth-masses on the inner transiting planet.

First circumbinary planet suitable for atmospheric characterization with JWST.

Abstract

We report the detection of a gas-giant planet in orbit around both stars of an eclipsing binary star system that also contains the smaller, inner transiting planet TOI-1338b. The new planet, called TOI-1338/BEBOP-1c, was discovered using radial-velocity data collected with the HARPS and ESPRESSO spectrographs. Our analysis reveals it is a $65.2~\rm{M_{\oplus}}$ circumbinary planet with a period of $215.5~$days. This is the first detection of a circumbinary planet using radial-velocity observations alone, and makes TOI-1338/BEBOP-1 only the second confirmed multiplanet circumbinary system to date. We do not detect the smaller inner transiting planet with radial-velocity data, and can place an upper limit on the inner planet's mass at $21.8~\mathrm{M}_\oplus$ with $99\%$ confidence. The inner planet is the first circumbinary planet amenable for atmospheric characterisation, using the James Webb Space Telescope.