Super-Earth streaks through red dwarf’s habitable zone

Astronomers have discovered a “super-Earth” orbiting a red dwarf just 37 light-years from our solar system.

Exoplanet Ross 508 b is gliding through its parent star’s so-called habitable zone, a region where surface temperatures allow the existence of liquid water, a key component of life. The newly discovered exoplanet has a mass about four times that of Earth and has been detected using a new infrared monitoring technique. This super-Earth’s proximity to our planet means it’s ripe for atmospheric exploration, which could help researchers determine whether life could exist around low-mass stars.

“That the very first planet discovered by this new method is so seductively close to the habitable zone seems too good to be true, and bodes well for future discoveries,” said team leader and Tokyo Institute of Technology professor Bunei Sato. .

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Red dwarfs such as Ross 508, which is about one-fifth the mass of the Sun, are small stars that make up about three-quarters of all the stars in our Milky Way galaxy. These stars are especially abundant around our solar system, making red dwarfs and their systems ideal for searching for planets outside the solar system and studying possible life elsewhere in the universe.

The fact that red dwarfs are small means that they are cold, with temperatures between 2000 and 3500 Kelvin. Their relatively low temperatures make them dim in visible light, unlike larger stars, and this means that astronomers must study them in the infrared.

To this end, the Center for Astrobiology in Japan has developed an infrared observing instrument called the Infrared Doppler Instrument (IRD) for installation on the Subaru Telescope in Hawaii. With this instrument, the world’s first high-precision infrared spectrograph for 8-meter-class telescopes, astronomers began looking for signs of planets around red dwarfs.

In particular, the researchers were looking for the characteristic “wobble” that an exoplanet induces in the orbit of its parent star; the wobble is recorded as a tiny shift in the wavelength of light from the star as it moves towards and away from Earth.

Artist rendering shows exoplanets orbiting a red dwarf. (Image credit: NASA/JPL-Caltech)

The opening of the Ross 508 b marks the first success of what is officially the IRD Subaru Strategic Program (IRD-SSP).

“It’s been 14 years since the development of the IRD began,” Sato said. “We continued our development and research in the hope of finding a planet exactly like Ross 508 b.”

Ross 508 b, only the third planet discovered around a star of such low mass, has an average distance from its parent star of just one-twentieth the distance between Earth and the Sun. The astronomers who discovered it believe that the planet’s highly elongated orbit takes it into the habitable zone of Ross 508 every 11 days.

“Ross 508 b is the first successful detection of a super-Earth using near-infrared-only spectroscopy,” Subaru Telescope researcher Hiroki Harakawa said in a statement. “Prior to this, when detecting low-mass planets such as super-Earths, near-infrared observations alone were not accurate enough, and verification with high-precision visible-light velocity measurements was necessary.” (Although super-Earths are larger than our own planet, most exoplanets currently discovered by scientists are much larger.)

Harakawa added that the study, of which he was the lead author, shows that even when working alone, the IRD-SSP is capable of detecting planets. He said the work particularly demonstrates the IRD-SSP’s advantage in its ability to detect planets with high precision even around late-type red dwarfs that are too faint to be observed in visible light.

The team’s research was published June 30 in the journal Publication of the Astronomical Society of Japan (PASJ).

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