TOI-512b: A Super-Earth Around a K-type Star
The search for exoplanets has led to thousands of discoveries, thanks to missions like Kepler and the Transiting Exoplanet Survey Satellite (TESS). These missions identify planets by detecting small dips in a star’s brightness when a planet passes in front of it. However, to truly understand these planets, astronomers need more than just their size—they need to determine their mass and composition as well. The ESPRESSO spectrograph, mounted on the Very Large Telescope (VLT), plays a crucial role in this process by measuring the gravitational influence planets exert on their stars, helping confirm their existence and characteristics.
In this study, Rodrigues et al. present the discovery of TOI-512b, a planet orbiting a bright K-type star. This planet was initially detected by TESS, and follow-up observations with ESPRESSO confirmed it as a super-Earth, a planet larger than Earth but smaller than Neptune.
Observations: Using TESS and ESPRESSO
TOI-512 was first observed by TESS in multiple observation campaigns spanning 2018 to 2021. The data revealed a repeating dip in the star's brightness every 7.19 days, suggesting a transiting planet. However, transit data alone could not confirm whether TOI-512b was a real planet or a false positive caused by another astronomical effect.
To verify the planet’s existence and measure its mass, the authors used ESPRESSO, a high-precision spectrograph. By analyzing how the star's motion changed due to the gravitational pull of an orbiting planet, the team confirmed TOI-512b and determined its mass with high accuracy.
Data Analysis and Planetary Characteristics
Rodrigues et al. modeled the transit data to estimate TOI-512b’s radius and then combined this information with radial velocity measurements from ESPRESSO to determine its mass. The planet has a radius of 1.54 times that of Earth and a mass of 3.57 Earth masses, giving it a density similar to Earth’s. This suggests that TOI-512b is a rocky planet with a composition likely dominated by silicates and metals.
One of the key findings is that TOI-512b falls into a category known as "super-Earths," which are planets larger than Earth but smaller than Neptune. These planets are especially interesting because they may be scaled-up versions of Earth or have thick atmospheres, making them prime targets for further study.
Understanding TOI-512b’s Internal Structure
Using the mass and radius, the authors explored what TOI-512b might be made of. Their models suggest it has a small core making up about 13% of its total mass, surrounded by a mantle that comprises about 69% of its mass. While the planet might have some water, the amount is relatively low, and it appears to lack a significant atmosphere, which is consistent with a world that has undergone mass loss due to intense stellar radiation over time.
No Second Planet?
Initially, TESS had reported a second possible planet in the system, labeled TOI-512.02, with a longer orbital period of 20.27 days. However, follow-up observations with ESPRESSO did not detect any evidence of this second planet in the radial velocity data. The authors conclude that TOI-512.02 was likely a false positive and does not exist.
Conclusions and Future Work
TOI-512b is an exciting addition to the growing list of known super-Earths. Its rocky nature and location in a relatively quiet system make it a strong candidate for future studies of planetary atmospheres. While current instruments, including the James Webb Space Telescope (JWST), may not be sensitive enough to study its atmosphere, future observatories could provide more insights. Additionally, studying its orbit and spin alignment could reveal details about how the system formed. This discovery highlights the importance of combining different methods—transit observations from TESS and radial velocity measurements from ESPRESSO—to build a complete picture of exoplanets.
Source: Rodrigues
