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An exoplanet in the habitable zone of a red dwarf
The exoplanet was discovered by the Japanese Subaru telescope as part of a new program to search for planets around small, dim stars.
A first exoplanet has been discovered by the Subaru Strategic Program using the infrared spectrograph IRD (InfraRed Doppler instrument) installed on the Subaru telescope of the National Astronomical Observatory of Japan, which observes the sky from the island of Hawaii. It was found in orbit around a red dwarf, stars smaller, less hot and less luminous than the Sun. Very numerous in the Milky Way, they are particularly numerous in our neighborhood but their environment is more difficult to explore.
In search of stable red dwarfs
The program to search for planets with the IRD instrument (developed by the Japan Astrobiology Center) began in 2019. The first step was to target many red dwarfs in search of the coldest ones, with surface temperatures around 3000°C, called late red dwarfs.
Once these were identified, the astronomers determined which ones were the most suitable for observations, i.e. the most stable. Indeed, this type of stars has a high surface activity, such as flares that can greatly disturb the measurements. Once the good candidates were catalogued, the second phase started with the systematic search for small planets in orbit around them.
About fifty stars are currently under surveillance and the first exoplanet has been identified around Ross 508, located 36 light-years from Earth and whose mass is about one fifth that of the Sun. The announcement is published in the journal Publications of the Astronomical Society of Japan.
Tiny oscillations in the velocity of Ross 508 have detected Ross 508b: an exoplanet with a mass about four times that of Earth. Its average distance from its central star is 0.05 times the Earth-Sun distance, and it is located at the inner edge of the habitable zone, the circumstellar region where water can theoretically remain in a liquid state on the surface of a star.
Moreover, with a highly elliptical orbit, Ross 508b could cross this zone with an orbital period of about 11 days. This particularity makes it a target of choice for future atmospheric studies to be conducted with more powerful telescopes. Very few planets have been identified by infrared spectroscopy around red dwarfs. This first one suggests that several other discoveries could soon be announced.
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