Temperate sub-Neptune found in orbit near red dwarf

Using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) and several terrestrial telescopes, astronomers have discovered and confirmed a sub-Neptune exoplanet near the habitable zone TOI-2285 (also known as TIC 329148988), an M dwarf star located 137 light-years away. in the constellation Cepheus. A paper describing the discovery will be published in Publications of the Astronomical Society of Japan.

An artist's impression of the sub-Neptune TOI-2285b and its parent star.  Image Credit: Sci-News.com.

An artist’s impression of the sub-Neptune TOI-2285b and its parent star. Image Credit: Sci-News.com.

“NASA’s Kepler space mission has revealed that planets the size of Earth and Neptune (planets the size of sub-Neptune) are abundant in dense orbits around stars other than the Sun,” Dr. Akihiko Fukui, an astronomer at the University of Tokyo and the Instituto de Astrofisica de Canarias, and colleagues wrote in their paper.

“Accurate radius measurements for these planets have found that the ‘hot’ sub-Neptune-sized planets are classified into two populations: one is warmer and smaller planets, and the other is cooler and larger planets, often referred to as super-Earths and mini-Neptunes, respectively. “

“Cooler sub-Neptune-sized planets also have an exciting potential for retaining liquid water under a hydrogen atmosphere, even though they are outside the habitable zone of rocky planets,” they added.

“If the planets have a water layer under the hydrogen atmosphere like Neptune and Uranus, then the hydrogen-water boundary could have the right conditions for water to be liquid.”

The newly discovered sub-Neptune has a radius of 1.74 times the radius of the Earth and a mass less than 19.5 times the mass of the Earth.

The planet, named TOI-2285b, has an orbital period of 27.3 days and is located just outside the habitable zone of the host star.

The alien world receives 1.54 times more light from the star than the Earth receives from the Sun.

“TOI-2285b is one of only a handful of low-insolation sub-Neptune planets passing bright host stars, among which LHS 1140b and TOI-1266c are the same size as the newly discovered planet with measured masses,” the astronomers wrote .

Although TOI-2285b is located just outside the habitable zone of a rocky planet, if the planet houses a water layer under a hydrogen-rich atmosphere, liquid water may exist on the surface of the water layer.

“The near-infrared bright host star makes this planet an excellent measure of additional radial velocity and atmospheric observations to improve our understanding of the composition, formation, and habitability of sub-Neptune-sized planets,” the scientists concluded.

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Akihiko Fukui et al. 2021. TOI-2285b: A planet with a 1.7 Earth radius near the habitable zone around an M dwarf nearby. Publ. Astron. Soc. Japan, In print; arXiv: 2110.10215

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