Astronomers from the Indian Institute of Astrophysics have found a new method to study the atmosphere of exoplanets.
To understand the atmosphere of extrasolar planets, Indian Astronomers have found a new method that shows planets going around stars other than the Sun can be studied by observing the polarization of light and studying polarisation signatures. These polarisation signatures or variations in scattering intensity of light can be observed with existing instruments and expanding the study of planets beyond the solar system using existing instruments.
In the research published in 'The Astrophysical Journal,' the scientists have developed a Python-based numerical code that incorporates a state-of-the-art planetary atmosphere model and employed all such asymmetries of an exoplanet orbiting the parent star at different inclination angles. They calculated the amount of polarization at different latitudes and longitudes of the planetary surface defined with respect to the disk centre and averaged them over the illuminated and rotation-induced oblate planetary surface. The polarization at different wavelengths is sufficiently high and hence can be detected even by a simple polarimeter if the starlight is blocked. It helps study the atmosphere of the exoplanets along with their chemical composition.
Aritra Chakrabarty, a postdoctoral researcher at IIA working with Sujan Sengupta, developed a detailed three-dimensional numerical method and simulated the polarization of exoplanets. Just like the Solar-planets, exoplanets are slightly oblate due to their rapid spin rotation. Further, depending on its position around the star, only a part of the planetary disk gets illuminated by the starlight. This asymmetry of the light-emitting region gives rise to non-zero polarization.
"Even if we cannot imagine the planet directly and the unpolarized starlight is allowed to mix up with the polarized reflected light of the planet, the amount should be a few ten parts of a million, but still can be detected by some of the existing high-end instruments such as HIPPI, POLISH, PlanetPol, etc. The research will help in designing instruments with appropriate sensitivity and guide the observers," said Aritra Chakrabarty.
Unlike the traditional and popular methods such as Transit Photometry and Radial Velocity methods that can detect planets that are viewed almost edge-on only, this polarimetric method can detect and probe exoplanets orbiting with a broad range of orbital inclination angles. Thus, polarimetric techniques in the near future will open up a new window for the study of the exoplanets and enable us to overcome many of the limitations of the traditional techniques.
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 "Indian astronomers find new method to study atmosphere of planets beyond Solar System")
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