Indian Scientists Discover A 'Hot-Jupiter' — Exoplanet 1.4 Times Bigger Than The Gas Giant

The newly discovered exoplanet, known as TOI 1789b, is located 725 light years away from Earth, and is orbiting very close to an evolved or aging star with a mass 1.5 times that of our Sun.

Representational image of an exoplanet | Photo: Getty

New Delhi: Scientists, part of an exoplanet search and study group at the Physical Research Laboratory (PRL) in Ahmedabad, have recently discovered an exoplanet larger in size than Jupiter. The newly discovered exoplanet, known as TOI 1789b, is located 725 light years away from Earth, and is orbiting very close to an evolved or aging star with a mass 1.5 times that of our Sun, according to a statement relesed by the Indian Space Research Organisation (ISRO).

The study, led by Professor Abhijit Chakraborty, was recently published in the Monthly Notices journal of the Royal Astronomical Society. 

The PARAS Optical Fiber-fed Spectrograph

The PRL Advanced Radial-velocity Abu-sky Search (PARAS) optical fiber-fed spectrograph on the 1.2 metre InfraRed Telescope at Mount Abu Observatory was used to make the discovery. A fiber optic spectrograph, which is used to measure the wavelength and line width of laser and a common light source, can accurately obtain the spectral characteristics of the light source.

The PARAS optical fiber-led spectrograph is the first of its kind in India, and can measure the mass of an exoplanet. The scientists carried out the measurements between December 2020 and March 2021.

The Exoplanet's Characteristics

The newly discovered exoplanet has a mass 70 per cent that of Jupiter, and a size 1.4 times that of the gas giant. In April 2021, the TCES Spectrograph from the Alfred Jensch Telescope in Germany was used for follow-up observations. A 43 cm telescope at PRL was also used to make independent observations. 

As per the Transiting Exoplanet Survey Satellite (TESS) catalogue, the host star of the exoplanet has been named TOI 1789b. In accordance to the Henry Draped catalogue, the star is known as HD 82139. Therefore, the planet is known as TOI 1789b or HD 82139b as per the International Astronomical Union nomenclature. 

The Indian scientists, along with collaborators from Europe and USA, found the newly discovered star-planet system to be very unique. The orbital period of the planet is just 3.2 days, and is very-very close to the star, the statement said. The planet is at a distance of 0.05 AU (Astronomical Units) from the star, which is roughly one-tenth the distance between the Sun and Mercury. 

Such exoplanets, which are a part of close-in systems, are rare. The planet is extremely hot, and has a surface temperature of around 2000 Kelvin, due to its proximity to the host star. Due to its hot surface temperature, it also has an inflated radius, and is one of the lowest density planets known. This is because the mass per unit volume reduces to a great extent. The planet has a density of 0.31 gram per cubic metres. 

A close-in exoplanet, with a distance less than 0.1 AU from the host star, and having a mass which is 0.25 times that of Jupiter, or is equivalent to a few Jupiter masses, is known as Hot-Jupiter. 

Hot Jupiters are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (P < 10 days). The close proximity to their stars and high surface-atmosphere temperatures resulted in the moniker "hot Jupiters".

Also, Hot-Jupiters are gas giant planets with orbital period less than 10 days. The short period means that hot Jupiters are very close to their host stars, usually less than 0.1 AU, one tenth of the distance between the Earth and the Sun. 

Why The Discovery Is Important

The detection of such systems will contribute to the understanding of mechanisms responsible for inflation in hot Jupiters and also provide an opportunity to understand the evolution of planets around stars, the study states.

This is the second exoplanet discovered by PRL scientists using the 1.2 metres telescope at Mount Abu Observatory. The first exoplanet which was discovered using this telescope is called K2-236b, has a size less than that of Saturn, and is located 600 light-years away from Earth.