Newly discovered exoplanet has exceptionally low density

An international team of astronomers, led by Stephanie Yoshida from the Harvard-Smithsonian Center for Astrophysics, has utilized NASA’s Transiting Exoplanet Survey Satellite (TESS) to identify a novel exoplanet in orbit around a distant star. This newfound celestial body, named TOI-1420 b, stands out due to its remarkably low density. The findings, presented in a paper published on September 18 via the arXiv pre-print server, shed light on the exciting discoveries made by TESS.

TESS’s primary mission is to survey approximately 200,000 of the brightest stars near our solar system, aiming to detect transiting exoplanets. To date, TESS has pinpointed nearly 6,800 potential exoplanets, known as TESS Objects of Interest (TOI), with 385 of them being officially confirmed.

In this recent breakthrough, astronomers identified a transit signal within the light curve of TOI-1420, a late G-dwarf star situated roughly 658 light years away. The planetary nature of this signal was validated through follow-up observations employing various telescopes.

The confirmed exoplanet, TOI-1420 b, exists in an exceptionally low-density state, with a radius of about 11.89 times that of Earth and a mass approximately 25.1 times that of our planet. This results in an extraordinarily low density of only 0.082 g/cm³. TOI-1420 b orbits its host star at a distance of 0.07 astronomical units (AU) and maintains an equilibrium temperature of approximately 957 Kelvin.

Notably, TOI-1420 b stands out as the largest-known planet with a mass under 50 Earth masses. Its low density suggests the presence of a significant envelope composed of hydrogen and helium. By employing planetary structure models, the researchers estimated that TOI-1420 b possesses a core mass of about 4.0 Earth masses, with the envelope making up the rest.

Turning our attention to the host star, TOI-1420, it bears similarities in size and mass to our sun. With an effective temperature of around 5,510 Kelvin and a metallicity level of 0.28, the star’s age is not precisely determined but is estimated to be less than 10.7 billion years.

In summary, the astronomers emphasized that low-density planets like TOI-1420 b offer exciting prospects for future atmospheric characterization and dynamical studies. These planets are more susceptible to outflows compared to higher-gravity planets. In the grander scheme, the comparative study of TOI-1420 b alongside other low-density worlds like WASP-107 b will help unravel their formation and evolution histories, offering valuable insights into the broader realm of planetary science.

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