NGTS-12b: A sub-Saturn mass transiting exoplanet in a 7.53 day orbit

TL;DR

NGTS-12b is a newly discovered long-period sub-Saturn exoplanet orbiting its star every 7.53 days, with unique properties near the Neptunian desert, and is suitable for atmospheric studies.

Contribution

This paper reports the discovery and characterization of NGTS-12b, the longest period exoplanet found by NGTS, combining transit and radial velocity data for detailed analysis.

Findings

NGTS-12b has a mass of 0.208 M_J and radius of 1.048 R_J.

It orbits its star every 7.53 days, the longest for NGTS.

The planet has a low density of 0.223 g/cm^3, near the Neptunian desert.

Abstract

We report the discovery of the transiting exoplanet NGTS-12b by the Next Generation Transit Survey (NGTS). The host star, NGTS-12, is a V=12.38 mag star with an effective temperature of T$_{\rm eff}$=$5690\pm130$ K. NGTS-12b orbits with a period of $P=7.53$d, making it the longest period planet discovered to date by the main NGTS survey. We verify the NGTS transit signal with data extracted from the TESS full-frame images, and combining the photometry with radial velocity measurements from HARPS and FEROS we determine NGTS-12b to have a mass of $0.208\pm0.022$ M$_{J}$ and a radius of $1.048\pm0.032$ R$_{J}$. NGTS-12b sits on the edge of the Neptunian desert when we take the stellar properties into account, highlighting the importance of considering both the planet and star when studying the desert. The long period of NGTS-12b combined with its low density of just $0.223\pm0.029$ g cm$^{-3}$ make it an attractive target for atmospheric characterization through transmission spectroscopy with a Transmission Spectroscopy Metric of 89.4.