A temperate Earth-sized planet with tidal heating transiting an M6 star

Area of Science:

• Exoplanetary science
• Astrobiology
• Stellar astrophysics

Background:

• Temperate Earth-sized exoplanets around late-M dwarfs are crucial for understanding planetary habitability.
• Detecting such planets is challenging, and few have been found, with systems like TRAPPIST-1 lacking evidence of volatiles.
• The small stellar radius of M dwarfs enhances atmospheric transit signatures, aiding exoplanet characterization.

Purpose of the Study:

• To report the discovery of a new temperate Earth-sized exoplanet, LP 791-18d, orbiting a cool M6 dwarf.
• To investigate the potential for hospitable climate conditions and water condensation on LP 791-18d.
• To characterize the planetary system, including the mass of a co-orbiting sub-Neptune, LP 791-18c.

Main Methods:

• Utilized transit timing variations (TTVs) to determine the masses of the exoplanets.
• Analyzed the orbital dynamics and gravitational interactions within the planetary system.
• Calculated the equilibrium temperature and radius of the discovered exoplanet, LP 791-18d.

Main Results:

• Discovered LP 791-18d, an Earth-sized exoplanet (1.03 R⊕) with an equilibrium temperature of 300-400 K.
• Determined the mass of the sub-Neptune LP 791-18c to be 7.1 ± 0.7 M⊕.
• Found that gravitational interactions cause non-circular orbits, leading to tidal heating and probable volcanism on LP 791-18d.

Conclusions:

• LP 791-18d represents a unique target for studying temperate exoplanets with potential for water condensation.
• The system provides an opportunity to investigate an exo-Earth interacting with a gas-rich sub-Neptune.
• Ongoing tidal heating suggests significant geological activity on LP 791-18d, impacting its potential habitability.