toi-396-three-planet-system-discovery

New Observations Reveal Insights into the TOI-396 Three-Planet System

An international team has studied a planetary system containing three exoplanets orbiting the star TOI-396. This groundbreaking research, published on November 22 on the pre-print server arXiv, offers the first mass measurements for these planets, enriching the understanding of the system's properties.

Overview of the TOI-396 Star System

Star Properties and Location

TOI-396 (HR 858 A), located about 103 light-years from Earth, is a bright star of spectral type F6 V. It has a size 26% larger and a mass 20% greater than the sun, an effective temperature of 6,354 K, and an estimated ago of two billion years. It is part of a binary system with a faint M dwarf companion, HR 858 B.

Exoplanet Discovery via NASA's TESS

In 2019, NASA's Transiting Exoplanet Survey Satellite (TESS) identified three exoplanets orbiting TOI-396, designated TOI-396 b, c, and d. Each of these planets, approximately twice Earth's size, was found within 0.1 AU of their host star, with orbital periods of 3.6, 6.0, and 11.2 days, respectively.

Observational Methods and Analysis

HARPS Radial Velocity Observations

Andrea Bonfanti of the Austrian Academy of Sciences in Graz, led a group of astronomers who used the HARPS spectrograph fro radial velocity studies of TOI-396 and analyzed NASA's TESS photometric data, revealing further details about the system.

Mass and Radius Measurement

"To determine the masses of the three planets, improve their radius estimates, and explore the possibility of Mean Motion Resonance (MMR) between planets b and c, we conducted HARPS radial velocity measurements of TOI-396 and analyzed archival high-precision photometric data from four TESS sectors," the researchers stated.

Findings from the Observations

Mass and Density of TOI-396 Planets

The observations revealed that TOI-396 and TOI-396 d have masses of approximately 3.55 and 7.1 Earth masses, respectively, corresponding to mean densities of 2.44 g/cm³ and 4.9 g/cm³. For TOI-396 c, only an upper mass limit of 3.8 Earth masses was determined, yielding a maximum density of 2.9 g/cm³.

Uniqueness of the TOI-396 System

The research underscores the uniqueness of the TOI-396 system, characterized by its mid-planet being the least dense and its outermost planet the most dense. Equilibrium temperatures for TOI-396 b, c, and d were estimated at 1,552 K, 1,309 K, and 1,061 K, respectively.

Dynamical Analysis of the System

Transit Timing Variations (TTV)

Additionally, the researchers conducted a Transit Timing Variation (TTV) dynamical analysis of the TOI-396 system. The analysis suggests that TOI-396 b and TOI-396 c may display TTVs with a super-period of approximately five years and semi-amplitudes of roughly two and five hours, respectively.

Conclusions and Future Implications

Atmospheric Characterization of TOI-396 Planets

In their concluding remarks, the researchers highlighted that all three planets orbiting TOI-396 exhibit favorable atmospheric characterization metrics, both in transmission and emission, among sub-Neptune exoplanets. This positions the TOI-396 system as an ideal setting for studying planetary formation and evolution.

Source

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