TOI-1842b: A Transiting Warm Saturn Undergoing Re-Inflation around an Evolving Subgiant

TL;DR

TOI-1842b is a low-density warm Saturn orbiting an evolving subgiant star, offering a prime target for atmospheric studies and testing models of gas giant re-inflation due to its unique properties.

Contribution

This paper reports the discovery and confirmation of TOI-1842b, a warm Saturn with exceptional atmospheric and orbital characteristics, and highlights its potential for atmospheric characterization and re-inflation studies.

Findings

Low-density with a large atmospheric scale height

Bright host star suitable for atmospheric observations

Short transit duration enabling easy scheduling

Abstract

The imminent launch of space telescopes designed to probe the atmospheres of exoplanets has prompted new efforts to prioritise the thousands of transiting planet candidates for follow-up characterisation. We report the detection and confirmation of TOI-1842b, a warm Saturn identified by TESS and confirmed with ground-based observations from Minerva-Australis, NRES, and the Las Cumbres Observatory Global Telescope. This planet has a radius of $1.04^{+0.06}_{-0.05}\,R_{Jup}$, a mass of $0.214^{+0.040}_{-0.038}\,M_{Jup}$, an orbital period of $9.5739^{+0.0002}_{-0.0001}$ days, and an extremely low density ($\rho$=0.252$\pm$0.091 g cm$^{-3}$). TOI-1842b has among the best known combinations of large atmospheric scale height (893 km) and host-star brightness ($J=8.747$ mag), making it an attractive target for atmospheric characterisation. As the host star is beginning to evolve off the main sequence, TOI-1842b presents an excellent opportunity to test models of gas giant re-inflation. The primary transit duration of only 4.3 hours also makes TOI-1842b an easily-schedulable target for further ground-based atmospheric characterisation.