A team of scientists from Ahmedabad's Physical Research Laboratory (PRL) , discovered a sub-Saturn or super-Neptune size planet around a Sun-like star, a report by ISRO said. The planet goes around the star in about 19.5days. The host star itself is about 600 light years away from the Earth. The discovery was made by measuring the mass of the planet using the indigenously designed “PRL Advance Radial-velocity Abu-sky Search” (PARAS) spectrograph integrated with 1.2m Telescope at PRL’s Gurushikhar Observatory in Mount Abu, India. This is the first of its kind spectrograph in the country, which can measure the mass of a planet going around a star and with this discovery India has joined a handful of countries, which have discovered planets around stars.
The surface temperature of the planet is around 600°C as it is very close to the host star (7 times nearer than Earth-Sun distance). This might make it unhabitable, but such a discovery is of importance for understanding the formation mechanism of such super-Neptuneor sub-Saturn kind of planets, that are too close to the host star, the report added.
The name of the host star is EPIC 211945201 or K2-236. Hence the planet will be known as EPIC 211945201b or K2-236b. Initially, the source was found to be a planetary candidate from NASA K2 (Kepler2) photometry because it was transiting, that is the planet body comes in between the star and the observer on Earth as it goes around the star and therefore it blocks a tiny amount of star-light, the ISRO report said.
By measuring the amount of light blocked by the planet body, we can measure the diameter or size of the planet, the report added. It was found to be 6 Earth radii. However, The K2 photometric data combined with false positive probability calculations was not sufficient to confirm the planetary nature of the system. Therefore, an independent measurement of the mass of the body was necessary for the discovery, which was made by the PARAS spectrograph.
The gravitational pull caused by a planet on its host star makes it wobble around their common center of mass, which shifts the spectra and can be measured in terms of Radial Velocity using precise and stabilised High Resolution Spectrographs, like the PARAS. The PRL scientists observed the target over a time-baseline of 420 days (in about 1.5 years) using the PARAS spectrograph for probing the nature of the system. By measuring the amplitude of the wobbling of the host star, the mass of the planet was found to be 27±14MEarth.
Based on the mass and radius, model-dependent calculations suggest that the heavy elements, like ice, silicates, and iron content is 60-70 % of the total mass. This detection is important as it adds to a sparse catalog of confirmed exoplanets with masses between 10-70 MEarth and radii between 4-8 REarth, whose masses and radii are measured to a precision of 50% or better. Only 23 such systems (including the present) are known to this date with such precise measurement of mass and radii.