The Age and High Energy Environment of the Very Young Transiting Exoplanet TOI 1227b

TL;DR

This study characterizes the young transiting exoplanet TOI 1227b and its host star, revealing rapid atmospheric mass loss driven by high-energy radiation, with implications for understanding early planetary evolution.

Contribution

It provides the first detailed age estimate of TOI 1227 and models the exoplanet's atmospheric mass loss, emphasizing the importance of follow-up measurements for understanding young exoplanet evolution.

Findings

TOI 1227 is approximately 8 million years old.

TOI 1227b is losing atmosphere at about 10^12 grams per second.

Future evolution of TOI 1227b depends on planetary mass assumptions.

Abstract

The mid-M star TOI~1227 hosts among the youngest known transiting exoplanets. We have conducted new X-ray imaging and optical spectroscopic observations of TOI 1227 aimed at ascertaining its age and the influence of its high-energy radiation on the exoplanet, TOI 1227b. We obtained a definitive X-ray detection of TOI 1227 with Chandra/HRC-I, and measured its Li and H$\alpha$ lines using ANU SSO 2.3 m telescope (WiFeS) spectroscopy. Through spatiokinematic, isochronal, and SED-based modeling, we have constrained the age of TOI 1227 as lying between 5 Myr and 12 Myr, with a best estimate of $\sim$8 Myr. In the context of this age, we model the evolution of the transiting exoplanet TOI 1227b, using the X-ray luminosity derived from Chandra HRC-I imaging. Our modeling suggests that TOI 1227b is currently undergoing rapid atmospheric mass loss at rates on the order of $\sim 10^{12}$ g s$^{-1}$. The modeling demonstrates that the exoplanet's predicted future evolution depends sensitively on assumptions for total and core planet mass, highlighting the importance of follow-up observations of the TOI 1227 star-exoplanet system to enable measurements of both planetary mass and mass-loss rate.