A hot super-Earth planet in the WASP-84 planetary system

TL;DR

This paper reports the discovery of a hot super-Earth planet, WASP-84 c, in the system of a known hot Jupiter, challenging the idea that hot Jupiters are usually solitary and suggesting diverse planetary formation scenarios.

Contribution

The study presents the first detection and validation of a close-in super-Earth companion to a hot Jupiter using combined TESS photometry and radial velocity data.

Findings

WASP-84 c is a 15 Earth-mass, 2 Earth-radius planet at 0.024 au.

The system includes a hot Jupiter and a hot super-Earth, indicating multiple planetary companions.

The presence of such companions suggests formation via disc migration or in-situ processes.

Abstract

Hot Jupiters have been perceived as loners devoid of planetary companions in close orbital proximity. However, recent discoveries based on space-borne precise photometry have revealed that at least some fraction of giant planets coexists with low-mass planets in compact orbital architectures. We report detecting a 1.446-day transit-like signal in the photometric time series acquired with the Transiting Exoplanet Survey Satellite (TESS) for the WASP-84 system, which is known to contain a hot Jupiter on a circular 8.5-day orbit. The planet was validated based on TESS photometry, and its signal was distilled in radial velocity measurements. The joint analysis of photometric and Doppler data resulted in a multi-planetary model of the system. With a mass of $15\, M_{\oplus}$, radius of $2\, R_{\oplus}$, and orbital distance of 0.024 au, the new planet WASP-84 c was classified as a hot super-Earth with the equilibrium temperature of 1300 K. A growing number of companions to hot Jupiters indicates that a non-negligible part of them must have formed under a quiescent scenario such as disc migration or in-situ formation.