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MIT astronomers have discovered a new planetary system “only” 33 light-years from Earth. Its star, an M-type dwarf, hosts at least two rocky planets similar to ours. Their potential for habitability is low as they orbit very close to their star, but this new nearby multiplanetary system gives scientists a new opportunity to study exoplanets and their atmospheres.
To date, the existence of more than 5,000 exoplanets has been confirmed in the Milky Way. However, the majority of them are gas-giant planets whose conditions in advance are not conducive to the emergence of life as we know it. Rocky worlds are of more interest to astrobiologists, but are harder to spot due to their relatively small size and mass. However, it is not one but two rocky planets that have recently been discovered around a cool red dwarf star named HD 260655.
They are more precisely two super-Earths, planets whose mass is between the Earth and a giant planet (though without exceeding 10 Earth masses). Several super-Earth species have already been discovered in other star systems – such as Gliese 876 d, Gliese 581 d, TOI-561 b or Kepler-69 c – but the planets orbiting HD 260655 offer exceptional observational conditions: The two planets in this system are each considered to be among the best targets for atmospheric study due to the brightness of their star. says Michelle Kunimoto, a researcher at MIT’s Kavli Institute for Astrophysics and Space Research.
Detection confirmed by several instruments
The two planets, called HD 260655 b and HD 260655 c, were discovered in October 2021 thanks to data from NASA’s TESS telescope, dedicated to the search for exoplanets. Detection is based on the planetary transit method, which consists of studying the variation in the brightness of a star: When a planet comes between the observational instrument and the star, it causes a brief decrease in its brightness, revealing its presence.
After detecting these decreases in brightness, Kunimoto and his collaborators checked whether the data matched readings from the ANDES High-Resolution Spectrograph (ArmazoNes High Scale Spectrograph) of the KECK telescope, located in Hawaii, and with those of the CARMENES spectrographs (Calar Alto High Resolution Search for M-Dwarfs with Exoearths with Near-Infrared and Optical Échelle Spectrographs), from the Calar Alto Observatory in Spain.
These extremely sensitive instruments are capable of detecting the small shifts that a star may make around its position, which are revealed by its light spectrum. When a planet orbits a star, it exerts a slight gravitational pull on it, causing a small periodic shift in its position. This method of detecting exoplanets, called the radial velocity method, makes it possible to estimate how far from the star the planet orbits, as well as its mass.
The data from TESS, ANDES and CARMENES thus made it possible to confirm that two exoplanets were in orbit around HD 260655. With a distance of 10 PCs, HD 260655 will be the fourth closest planetary system after HD 219134, LTT 1445 A and AU Mic, «states the researchers in their pre-printed paper.
Potential other worlds to discover in this system
The data also made it possible to partially characterize these two planets. Their magnitude can be estimated from the amount of light blocked during transit, while their mass is calculated from the speed of the star moving around its position.
The star’s closest exoplanet, HD 260655 b, completes a full orbit of 2.8 days; it is about 1.2 times the size of the Earth, and its mass corresponds to two masses of earth. The orbit for HD 260655 c lasts 5.7 days; it is 1.5 times larger than Earth and weighs three masses of soil. These dimensions suggest densities similar to those of Earth and therefore that they are terrestrial planets.
However, it is unlikely that any kind of life – at least life as we know it on our planet – exists in these worlds. Although the star HD 260655 is weaker and cooler than our sun, these planets orbit it too close. As a result, surface temperatures are extremely hot: 435 ° C on average at HD 260655 b and 284 ° C at HD 260655 c. ” We consider this beach outside the habitable zone to be too hot for liquid water to exist on the surface “says Kunimoto.
Scientists remain optimistic that there may be more planets in this system. ” There are many multi-planetary systems that host five or six planets, especially around small stars like this one. Hopefully we will find more who will be in the habitable zone said Avi Shporer, one of the team behind the discovery.
Meanwhile, the team is looking forward to taking a closer look at the atmospheres of these planets with the James Webb Telescope, to possibly discover various volatile materials, including carbon-based species.