Scientists at ISRO Uncover Exoplanet Larger Than Jupiter

Scientists from the Ahmedabad-based Physical Research Laboratory (PRL), specializing in exoplanet exploration and research, have identified a novel exoplanet orbiting in close proximity to an evolved star with a mass 1.5 times that of the Sun, situated 725 light years away. This discovery, facilitated by the PRL Advanced Radial-velocity Abu-sky Search (PARAS) optical fiber-fed spectrograph, the inaugural instrument of its kind in India, was conducted on the 1.2-meter Telescope at PRL’s Mt. Abu Observatory, as reported by the Indian Space Research Organisation (ISRO).

Leveraging the capabilities of PARAS to measure the mass of the exoplanet, the team determined that the newfound planet possesses a mass approximately 70 percent that of Jupiter, with a size 1.4 times that of Jupiter. The observations were conducted between December 2020 and March 2021, with additional measurements acquired from the TCES spectrograph in Germany and independent photometric observations from PRL’s 43-cm telescope at Mt. Abu in April 2021. The host star is cataloged as HD 82139 in the Henry Draper catalogue and TOI 1789 in the TESS catalogue, leading to the exoplanet being designated as TOI 1789b or HD 82139b according to IAU nomenclature.

The discovery team, headed by Prof. Abhijit Chakraborty, comprises students, team members, and international collaborators from Europe and the US. The unique star-planet system features an exceptionally short orbital period, with the planet completing an orbit around the host star in just 3.2 days, placing it at an extremely close distance of 0.05 AU (roughly one-tenth the distance between the Sun and Mercury).

This system is among the less than 10 known close-in systems among the multitude of exoplanets discovered to date. Due to its close proximity to the star, the exoplanet experiences intense heating, resulting in a surface temperature reaching up to 2000 K and an inflated radius. Notably, it is recognized as one of the least dense planets known, with a density of 0.31 grams per cc. Described as a “Hot-Jupiter,” this type of close-in exoplanet with a mass ranging from 0.25 to a few times that of Jupiter is characterized by its proximity to the host star (within 0.1 AU).

ISRO highlighted that the detection of such a system contributes to our understanding of the mechanisms leading to inflation in Hot-Jupiters and the formation and evolution of planetary systems around aging and evolving stars. This marks the second exoplanet discovery by PRL scientists using PARAS at the 1.2-meter Mt. Abu telescope, following the identification of the sub-Saturn size exoplanet K2-236b at a distance of 600 light-years in 2018.

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