TESS Discovery of a Transiting Super-Earth in the $π$ Mensae System

Abstract: We report the detection of a transiting planet around $\pi$ Mensae (HD 39091), using data from the Transiting Exoplanet Survey Satellite (TESS). The solar-type host star is unusually bright (V=5.7) and was already known to host a Jovian planet on a highly eccentric, 5.7-year orbit. The newly discovered planet has a size of $2.04\pm 0.05$ $R_\oplus$ and an orbital period of 6.27 days. Radial-velocity data from the HARPS and AAT/UCLES archives also displays a 6.27-day periodicity, confirming the existence of the planet and leading to a mass determination of $4.82\pm 0.85$ $M_\oplus$. The star's proximity and brightness will facilitate further investigations, such as atmospheric spectroscopy, asteroseismology, the Rossiter--McLaughlin effect, astrometry, and direct imaging.

• The paper documents the discovery of a 2.04 ± 0.05 R⊕ transiting super-Earth with a 6.27-day orbit around the bright G0V star π Mensae.
• The paper employs TESS photometry in combination with HARPS and AAT/UCLES radial velocity data to precisely measure its mass at 4.82 ± 0.85 M⊕.
• The paper highlights the system’s potential for atmospheric characterization and dynamical studies due to the host star’s brightness and proximity.

TESS Discovery of a Transiting Super-Earth in the $\pi$ Mensae System

The paper "TESS Discovery of a Transiting Super-Earth in the $\pi$ Mensae System" documents the identification of a new exoplanet within the $\pi$ Mensae system, facilitated by data from the Transiting Exoplanet Survey Satellite (TESS). The discovery is significant due to the host star's brightness, a G0V star designated HD 39091, which offers unique opportunities for detailed follow-up observations.

Discovery and Confirmation

The planet, detected via TESS's photometric survey, exhibits a size of $2.04 \pm 0.05 R_\oplus$, with an orbital period of 6.27 days. The host star, being exceptionally bright ($V = 5.7$), allows for high-quality observational data, critical for validation. Complementary radial velocity data from the HARPS and AAT/UCLES archives confirm the planet's existence through the same periodicity and provide a mass estimate of $4.82 \pm 0.85 M_\oplus$. This decisive confirmation is critical given the propensity for false positives in transit detection.

Scientific Implications

This discovery has several notable implications:

1. Mass and Composition Insights: The mass and radius suggest a composition potentially not purely rocky, hinting at a thin H/He envelope or substantial volatile components. This aligns with models for super-Earths, which propose varied compositions beyond purely silicate-based planets.
2. Bright Host Star Advantages: The star's brightness makes it a prime candidate for atmospheric characterization via spectroscopy, notably with upcoming James Webb Space Telescope (JWST) missions. The anticipated occultation depth provides an opportunity for detailed thermal emission studies.
3. Stellar and Planetary Dynamics Analysis: The system's dynamics are particularly intriguing given the presence of a known giant planet on a long-period, eccentric orbit. This provides a laboratory for studying planetary formation theories regarding planet migration and interactions within multi-planet systems.
4. Proximity Enables Diverse Observations: The star's proximity (18.27 pc) facilitates numerous investigative avenues including asteroseismology, direct imaging, and the Rossiter-McLaughlin effect to gauge spin-orbit alignment. These are pivotal for understanding the broader dynamics and history of the planetary system.

Future Prospects

Continued observations, particularly additional TESS data, will refine the planet’s parameters, and may unveil other planets in the system. Potential spectroscopic observations by JWST could revolutionize our understanding of planet c's atmospheric composition and thermal properties. Moreover, astrometric data from Gaia might offer insights into the three-dimensional arrangement of the planetary orbits, enriching our understanding of the system's long-term dynamical evolution.

Conclusion

The discovery of the $\pi$ Mensae system's transiting super-Earth marks an advancement in the field of exoplanetary studies, presenting robust opportunities for subsequent analytical pursuits. The synergy between TESS's detection capabilities and the astrophysical community's extensive follow-up potential promises to leverage this discovery in seeking deeper insights into exoplanet compositions and orbital dynamics. This discovery exemplifies how bright nearby stars with transiting exoplanets serve as gateways for detailed planetary science beyond our solar system.