Moving beyond the solar system to exoplanets

An artist's rendering of the Kepler space telescope in space.  

Ever since the first exoplanet (51 Pegasi b) was discovered in 1995 by Michael Mayor and Didier Queloz, there has been renewed activity and interest in this field. The Kepler and K2 missions of NASA have identified thousands of planet candidates. Now there are nearly 5,000 planet candidates, and of these, some 3,397 have been confirmed as planets, according to the NASA exoplanet archive.

The latest entry into the list of confirmed exoplanets is Kepler-56 d, which was added on 13 October. This planet has an orbital period of 1,002 days, accurate to five days, and a mass of nearly 5.61 times that of Jupiter. It is a massive planet that orbits its star Kepler-56 whose radius is about 4.23 times the sun’s radius and which is about 1.32 times as massive as the sun. This planet is only the third to be discovered orbiting its star Kepler-56. Being very massive, its presence was originally inferred by the periodic changes in Kepler-56’s radial velocity. The star itself is a red giant, much larger but dimmer than our sun, and this system is unlike the majority of known star systems hosting planets in that the axes of revolution of two of its planets (Kepler-56 b and c) are tilted with respect to the stars axis by 45 degrees. It was this tilting that led to the inference, and later discovery, of the existence of a massive third planet.

The discovery of these systems that differ from our solar system has led to astronomers rethinking their models of the origin and structure of planetary systems. While initially, based on the structure of our solar system with its eight planets, scientists believed that smaller rocky planets would form closer to the star and huge, massive, gaseous ones would orbit at a distance, this belief was shaken by the very first exoplanet seen – 51 Pegasi b. This planet has about half the mass of Jupiter and orbits its star at close quarters – only about 0.05 Astronomical Units (AU, one astronomical unit is the average distance between the earth and the sun).

Indian efforts in studying both theory and observations are sizeable, from looking out for exoplanets in the Mount Abu Infrared Observatory and through Astrosat, to theoretical work on evolution of the solar system and methods of detecting exomoons, as was evidenced by the presentations in the IIA-ISAC National Symposium on Exoplanets, held in Kodaikanal, earlier this month.

Much discussed were the Indian facilities, especially, the PARAS-1 spectrograph, which is part of the Mount Abu Infrared Observatory which hosts a 1.2-metre telescope, focussed on detecting exoplanets. This unit began taking data in 2012. Located at an altitude of about 1,700 m, this spectrograph enjoys around 220 cloudless nights each year. This facility is soon to be upgraded with a 2.5 m telescope, and PARAS-2, as it is known, is expected to see first light in 2020.

Models of exoplanets show that there are 14 types of planets. These can be pure water planets, carbon planets, hydrogen planets, and so on. Our solar system has only five types, perhaps as an indication that if we must expect something, it is the unexpected!

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Printable version | Sep 26, 2021 1:01:25 PM |

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