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BENGALURU: Astronomers from the Indian Institute of Science (IISc), an autonomous institute of the Department of Science and Technology (DST) have found a new method to understand the atmosphere of extrasolar planets.
The team has shown that 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, the DST said.
In the recent past, astronomers have discovered that many other stars have planets — till now, around 5,000 such exoplanets have been detected — going around them, like our solar system.
“About a couple of decades ago, Sujan Sengupta, an IIA scientist suggested that the thermal radiation of hot young planets and the reflected light of planets orbiting other stars, known as extra-solar planets or exoplanets would also be polarized and the measure of the polarization might unveil the chemical composition and other properties of the exoplanetary atmosphere,” the DST said.
Subsequent confirmation of the prediction by the detection of polarization of many Brown Dwarfs — a kind of failed stars that have an atmosphere very similar to that of Jupiter — motivated researchers all over the world to build highly sensitive polarimeters and use polarimetric methods to probe exoplanetary environments.
“Recently, 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,” the DST added.
Further, the team found that 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.
“In the research published in ‘The Astrophysical Journal,’ 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 DST said.
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.
“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,” Aritra Chakrabarty said.
The astronomers said that unlike traditional and popular 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.
The team has shown that 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, the DST said.
In the recent past, astronomers have discovered that many other stars have planets — till now, around 5,000 such exoplanets have been detected — going around them, like our solar system.
“About a couple of decades ago, Sujan Sengupta, an IIA scientist suggested that the thermal radiation of hot young planets and the reflected light of planets orbiting other stars, known as extra-solar planets or exoplanets would also be polarized and the measure of the polarization might unveil the chemical composition and other properties of the exoplanetary atmosphere,” the DST said.
Subsequent confirmation of the prediction by the detection of polarization of many Brown Dwarfs — a kind of failed stars that have an atmosphere very similar to that of Jupiter — motivated researchers all over the world to build highly sensitive polarimeters and use polarimetric methods to probe exoplanetary environments.
“Recently, 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,” the DST added.
Further, the team found that 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.
“In the research published in ‘The Astrophysical Journal,’ 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 DST said.
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.
“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,” Aritra Chakrabarty said.
The astronomers said that unlike traditional and popular 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.
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