Astronomers in India have discovered an exoplanet larger than Jupiter with exceptionally hot temperatures and a very short orbital period. Named TOI 1789b, the planet is located about 725 light-years away from us and is orbiting a star that is approximately 1.5 times the size of our sun.
This discovery was made by the exoplanet search and study group at the Physical Research Laboratory (PRL), Ahmedabad. Astronomers detected the planet by using the Advanced Radial-velocity Abu-sky Search (PARAS) optical fibre-fed spectrograph.
Based on their observations, they confirmed that TOI 1789b is approximately 1.4 times larger than Jupiter and about 70% of its mass. Additional observations conducted with the TCES spectrograph in Germany revealed that it has an exceptionally short orbital period of only 3.2 days. This means that it is very close to its host star at a distance of just 0.05 astronomical units (AU) – one AU is the distance of Earth to our sun. To put this into better perspective, TOI 1789b orbits its star at about one-tenth of the distance that Mercury orbits our sun.
Since it is so close to its star, it has an incredibly hot surface temperature that can reach as high as 2,000 Kelvin (3,140 degrees Fahrenheit or 1,727 degrees Celsius). This extreme heat causes its radius to be inflated as explained by the astronomers in their paper, “The detection of such system enhances our understanding of various mechanisms responsible for inflation in hot Jupiters and the formation and evolution of planetary systems around evolving and ageing stars.”
They added, “It is one of the few nearby evolved stars with a close-in planet. The detection of such systems will contribute to our understanding of mechanisms responsible for inflation in hot Jupiters and also provide an opportunity to understand the evolution of planets around stars leaving the main sequence branch.”
As a matter of fact, according to the Indian Space and Research Organisation (Isro), there are less than ten close-in systems that have been found among all the exoplanets detected thus far.
The study was published in the journal Monthly Notices of the Royal Astronomical Society where it can be read in full.
Interestingly, this is actually the second exoplanet detected by scientists at the PRL using the PARAS at 1.2 m Mount Abu telescope. Named K2-236b, it was first discovered in 2018 and later observed between December 2020 and March 2021. The sub-Saturn planet is located approximately 600 light-years away from us. It is about 27 times the mass of our planet and around 6 times the radius. Its surface temperature is about 600 degrees Celsius (1,112 degrees Fahrenheit) and it takes 19.5 days to orbit its star.