Using data from NASA's Transiting Exoplanet Survey Satellite (TESS), astronomers from the Physical Research Laboratory (PRL) in Ahmedabad, India, along with international collaborators, have discovered a new sub-Saturn exoplanet exhibiting an unusually high density. The discovery, detailed in a research paper published on September 2 in the Astronomy & Astrophysics journal, sheds new light on the complex processes involved in planet formation.
TESS and Its Mission
TESS is designed to survey approximately 200,000 of the brightest stars near the Sun in search of transiting exoplanets. To date, TESS has identified over 7,200 potential exoplanets, known as TESS Objects of Interest (TOI), with 545 of these candidates confirmed. The latest addition to this growing list is TOI-6651 b, a dense sub-Saturn exoplanet orbiting a subgiant G-type star located about 690 light-years from Earth.
Discovery and Characterization of TOI-6651 b
Led by Sanjay Baliwal from PRL, the team detected a transit signal in the light curve of TOI-6651, a metal-rich subgiant G-type star approximately 3.7 billion years old. The planetary nature of this signal was confirmed through follow-up observations using ground-based facilities, leading to the identification of TOI-6651 b.
“We presented the discovery and characterization of a dense sub-Saturn exoplanet, TOI-6651 b, transiting a metal-rich G-type sub-giant star,” the researchers noted.
According to the study, TOI-6651 b has a radius of about 5.09 Earth radii and a mass 61 times that of Earth, resulting in a bulk density of approximately 2.52 g/cm³. This makes TOI-6651 b the densest sub-Saturn identified by TESS so far.
Orbital and Physical Characteristics
TOI-6651 b orbits its host star every 5.05 days at a distance of about 0.06 AU, with an orbital eccentricity of 0.09. The planet's equilibrium temperature is estimated to be 1,493 K, making it a hot exoplanet with extreme conditions.
The researchers estimate that TOI-6651 b possesses a core mass of around 53 Earth masses, suggesting that the planet is predominantly composed of dense materials such as rock and iron, which constitute about 87 percent of its total mass. The remaining mass likely consists of a low-density hydrogen/helium envelope.
Characteristics of the Host Star TOI-6651
The host star, TOI-6651, has a radius of approximately 1.32 solar radii and a mass of 1.72 solar masses. It exhibits an effective temperature of 5,940 K and has a metallicity of 0.225 dex, indicating a relatively high metal content, which is often associated with planet formation.
Challenges to Planet Formation Theories
The discovery of TOI-6651 b presents a significant challenge to existing theories of planet formation. The researchers propose that the planet's unusual density could be the result of merging events or significant atmospheric mass loss driven by tidal heating. These processes underscore the complex interplay of dynamical forces and atmospheric evolution that contribute to the formation of massive, dense sub-Saturn exoplanets.
“The existence of TOI-6651 b challenges conventional planet formation theories and could be a result of merging events or significant atmospheric mass loss through tidal heating, highlighting the complex interplay of dynamical processes and atmospheric evolution in the formation of massive dense sub-Saturns,” the scientists concluded.
This discovery not only broadens our understanding of sub-Saturn exoplanets but also provides valuable insights into the intricate mechanisms that govern planet formation and evolution in our universe.
More information: Sanjay Baliwal et al., Discovery and characterization of a dense sub-Saturn TOI-6651 b, Astronomy & Astrophysics (A&A) (2024). DOI: 10.1051/0004-6361/202450934.
Journal information: Astronomy & Astrophysics
English (United States) ·