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MIT astronomers have discovered a new planetary system “only” 33 light-years from Earth. Its star, an M-type dwarf, has at least two rocky planets similar in size to ours. Their potential for habitat is small, as they orbit very close to their star, but this new near multiplanetary system offers scientists a new opportunity to study exoplanets and their systems. atmosphere.
To date, the existence of more than 5000 exoplanets has been confirmed in the Milky Way. However, most of these are gas giants, whose conditions are a priori unsuitable for the emergence of life as we know them. The rocky worlds are more interested in astrobiologists, but are more difficult to find because of their small size and mass. However, it is not one, but two rocky planets recently discovered around a cool red dwarf star named HD 260655.
They are more precisely two super-Earths, planets whose mass is between that of Earth and a giant planet (with nothing exceeding 10 terrestrial masses). Many super-Earths have been discovered in other star systems-such as Gliese 876 d, Gliese 581 d, TOI-561 bo Kepler-69 c-but the planets orbiting around HD 260655 offer a unique observation conditions: The two planets in this system are each considered one of the most popular targets for atmospheric studies because of the brightness of their star. said Michelle Kunimoto, a researcher at MIT’s Kavli Institute for Astrophysics and Space Research.
Detection confirmed by multiple instruments
The two planets, called HD 260655 b and HD 260655 c, were spotted in October 2021, thanks to data from NASA’s TESS telescope, dedicated to finding exoplanets. Detection is based on the planetary transit method, which consists of the study of the change in the brightness of a star: when a planet comes between the observation instrument and the star, it causes a momentary drop in its light. reveals its presence.
After detecting these light reductions, Kunimoto and his colleagues checked whether the data matched the readings from the ANDES High-Resolution Spectrograph (ArmazoNes High Dispersion Scale Spectrograph) with the KECK telescope, located in Hawaii, and with the CARMENES spectrographs (Calar Alto high-Resolution search for M dwarf with Exoearths with Near-infrared and optical Échelle Spectrographs), from the Calar Alto observatory in Spain.
These highly sensitive instruments are able to record the minute transitions that can be made by a star around its position, which are revealed by its light spectrum. When a planet orbits a star, it has little attraction to its gravity, causing a small change in its position. This method of identifying exoplanets, called the radial velocity method, makes it possible to estimate how far from the star the planet orbits, as well as its mass.
Data from TESS, ANDES and CARMENES, thus make it possible to confirm that two exoplanets are in orbit around HD 260655. At a distance of 10 pc, the HD 260655 became the fourth closest transiting planetary system after the HD 219134, LTT 1445 A, and AU Mic, “the researchers stated in their preprint paper.
Potentially other worlds to be discovered in this system
The data also make it possible to partially characterize these two planets. Their size can be estimated from the amount of light blocked during travel, while their mass is calculated based on the speed of the star moving around its position.
The closest exoplanet to the star, HD 260655 b, will complete an entire orbit in 2.8 days; it is about 1.2 times the size of the Earth and its weight is equal to two masses of the Earth. The orbit of HD 260655 c will last 5.7 days; it is 1.5 times the size of the Earth and weighs three times the mass of the Earth. These dimensions suggest densities similar to Earth and therefore they are terrestrial planets.
However, it is likely that any form of life — at least, life that we know of on our planet — exists in these worlds. Although the star HD 260655 is dimmer and cooler than our Sun, these planets orbit very close to it. As a result, the surface temperatures are very hot: 435 ° C on average in HD 260655 b and 284 ° C in HD 260655 c. ” We consider this beach to be outside the residential zone, too hot for the liquid water on the surface. “said Kunimoto.
Researchers remain optimistic that there are more planets in this system. ” There are many multiplanetary systems that host five or six planets, especially around small stars like these. Hopefully we will see more, which is in the habitable zone said Avi Shporer, one of the team behind the discovery.
Meanwhile, the team expects to take a closer look at the atmospheres of these planets using the James Webb Telescope, to possibly detect a variety of volatile materials, including carbon-based species.