Introduction

An international team of astronomers has recently unveiled significant findings regarding the planetary system TOI-396, which consists of three exoplanets orbiting the bright star located approximately 103 light years away from Earth. This promising study, published on November 22, provides the first mass measurements for the trio of planets, deepening our understanding of their characteristics and the dynamics of the entire system.

The Star TOI-396

TOI-396, also known as HR 858 A, is a spectral type F6 V star that is about 26% larger and 20% more massive than our Sun. Approximately two billion years old, it has an effective surface temperature of 6,354 K. Intriguingly, TOI-396 is part of a binary system, sharing its cosmic neighborhood with a faint companion star known as HR 858 B.

Discovery of Exoplanets

The discovery of three exoplanets—designated TOI-396 b, TOI-396 c, and TOI-396 d—dates back to 2019 when they were detected by NASA’s Transiting Exoplanet Survey Satellite (TESS). These intriguing worlds are roughly twice the size of Earth and orbit exceptionally close to their host star, within a radius of just 0.1 AU. The orbital periods of these planets are 3.6 days for TOI-396 b, 6.0 days for TOI-396 c, and a longer 11.2 days for TOI-396 d.

Recent Study and Findings

In this recent study, led by Andrea Bonfanti from the Austrian Academy of Sciences, the researchers conducted detailed radial velocity observations of TOI-396 using the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph. They also analyzed precise photometric data from TESS, allowing for a more comprehensive understanding of the planets' properties.

To estimate the masses of these exoplanets and refine their radii, the team focused on the radial velocity observations and retrieved high-precision transit data. Their findings revealed that TOI-396 b has a mass of 3.55 Earth masses and TOI-396 d weighs in at 7.1 Earth masses. This indicates a mean density of about 2.44 g/cm³ for TOI-396 b and a much higher density of 4.9 g/cm³ for TOI-396 d. Interestingly, only an upper limit mass of about 3.8 Earth masses was determined for TOI-396 c, resulting in a maximum density of 2.9 g/cm³.

Unusual Density Distribution

One of the standout discoveries from this research is the unusual density distribution within the TOI-396 system, where the mid planet (TOI-396 c) is less dense than the outermost planet (TOI-396 d). This peculiarity supports the notion that TOI-396 is a unique laboratory for studying planetary formation and evolution.

Equilibrium Temperatures

The study further calculated the equilibrium temperatures for the three planets, estimated at 1,552 K for TOI-396 b, 1,309 K for TOI-396 c, and 1,061 K for TOI-396 d. These temperatures illuminate the atmospheres of the planets and their potential for hosting water or other life-sustaining elements.

Transit Timing Variation Analysis

Additionally, a transit timing variation (TTV) dynamical analysis indicated that TOI-396 b and TOI-396 c could experience TTVs with a super-period of about five years, showcasing oscillations with semi-amplitudes of roughly two and five hours, respectively.

Conclusion

In conclusion, the authors of this illuminating study highlighted that the planets orbiting TOI-396 possess favorable characteristics for atmospheric characterization, both during transmission and emission phases. This exceptional three-planet system presents an outstanding opportunity for scientists to delve deeper into our understanding of planetary systems, their formation, and their evolution over time. The TOI-396 system is poised to be a focal point for future exoplanetary research, bringing us closer to uncovering the mysteries of worlds beyond our own!