The ultralight, ultra-fast exoplanet is unlike anything in our solar system

The exoplanet GJ 367b orbits its star in an extremely short time. Only 8 hours, then a year has passed on this planet. We don’t know anything like it about our solar system: Mercury is the fastest planet here with an orbital period of 88 days, compared to GJ 367b, it’s a lame snail. GJ 367b is a rocky planet much denser than Earth and similar in structure to Mercury. He probably has a big iron core. This precise characterization is based on high precision measurements of radius and mass – which is not obvious for exoplanets. GJ 367b orbits a dwarf star that is about half the size of the Sun. The radiation on the planet is enormous due to the short distance to the star: On the side of the planet facing the star, the temperature is between 1300 ° and 1500 ° Celsius. At such temperatures, iron and rocks melt. Credit: SPP 1992 (Patricia Klein)

When it comes to extrasolar planets, ‘GJ 367 b’ is a featherweight. With half the mass of Earth, the newly discovered planet is one of the lightest of the nearly 5,000 exoplanets known today. It takes about eight hours for the extrasolar planet to orbit its mother star. With a diameter of just over 9,000 kilometers, GJ 367 b is slightly larger than ">March. The planetary system is located just under 31 light years from Earth and is therefore ideal for further investigation. The discovery demonstrates that it is possible to accurately determine the properties of the smallest and least massive exoplanets. Such studies provide a key to understanding how the terrestrial planets form and evolve.

An international group of 78 researchers led by Kristine WF Lam and Szilárd Csizmadia of the DLR (German Aerospace Center) Planetary Research Institute reports the results of their studies in the scientific journal Science. With an orbital period of only one third of an Earth day, GJ 367 b is evolving rapidly. “Based on the precise determination of its radius and mass, GJ 367b is classified as a rocky planet,” reports Kristine Lam. “It seems to have similarities with Mercury. This places it among the terrestrial planets smaller than Earth and advances research in the search for a “second Earth”.

More precise exoplanet trackers possible

A quarter of a century after the first discovery of an extrasolar planet, attention has shifted to characterizing these planets more precisely, in addition to making new discoveries. At present, it is possible to construct a much more precise profile for most of the known exoplanets. Many exoplanets have been discovered using the transit method – the measurement of minute differences in the light emitted, or its apparent magnitude, from a star as a planet passes in front of it (relative to the observer) . GJ 367 b was also discovered using this method, with the help of ">NasaSatellite for the study of exoplanets in transit (TEST).

The origin of the small fast planets still unknown

GJ 367 b belongs to the group of “ultra-short-lived” (USP) exoplanets that orbit their star in less than 24 hours. “We already know a few, but their origins are currently unknown,” says Kristine Lam. “By measuring the precise fundamental properties of the planet USP, we can gain insight into the history of the formation and evolution of the system.” Following the discovery of this planet using TESS and the transit method, the spectrum of its star was then studied from the ground using the radial velocity method. The mass was determined using the HARPS instrument on the 3.6 m telescope of the European Southern Observatory. Through the meticulous study and the combination of different evaluation methods, the radius and mass of the planet were determined with precision: its radius is 72% of the radius of the Earth and its mass is 55% of the mass of the Earth.

Highest precision for radius and mass

By determining its radius and its mass with a precision of 7 and 14 percent respectively, the researchers were also able to draw conclusions about the exoplanetthe internal structure of. It is a rocky planet of low mass, but has a higher density than Earth. “The high density indicates that the planet is dominated by an iron core,” says Szilárd Csizmadia. “These properties are similar to those of Mercury, with its disproportionate iron and nickel core that sets it apart from other terrestrial bodies in the solar system.” However, the planet’s proximity to its star means it is exposed to an extremely high level of radiation, more than 500 times stronger than what Earth is experiencing. The surface temperature can reach up to 1500 degrees Celsius – a temperature at which all rocks and metals would be melted. GJ 367 b cannot therefore be considered as a “second Earth”.

The parental star is a “red dwarf”

The mother star of this newly discovered exoplanet, a red dwarf called GJ 367, is only about half the size of the Sun. This was beneficial for its discovery because the transit signal of the orbiting planet is particularly important. Red dwarfs are not only smaller, but also cooler than the Sun. This makes their associated planets easier to find and characterize. They are among the most common stellar objects in our cosmic neighborhood and are therefore suitable targets for research on exoplanets. Researchers estimate that these red dwarfs, also known as “M-class stars,” orbit two to three planets on average.

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Reference: “GJ 367b: A dense ultra-short period sub-Earth planet transiting a near red dwarf star” by Kristine WF Lam, Szilárd Csizmadia, Nicola Astudillo-Defru, Xavier Bonfils, Davide Gandolfi, Sebastiano Padovan, Massimiliano Esposito, Coel Hellier , Teruyuki Hirano, John Livingston, Felipe Murgas, Alexis MS Smith, Karen A. Collins, Savita Mathur, Rafael A. Garcia, Steve B. Howell, Nuno C. Santos, Fei Dai, George R. Ricker, Roland Vanderspek, David W Latham, Sara Seager, Joshua N. Winn, Jon M. Jenkins, Simon Albrecht, Jose M. Almenara, Etienne Artigau, Oscar Barragán, François Bouchy, Juan Cabrera, David Charbonneau, Priyanka Chaturvedi, Alexander Chaushev, Jessie L. Christiansen, William D. Cochran, José R. De Meideiros, Xavier Delfosse, Rodrigo F. Díaz, René Doyon, Philipp Eigmüller, Pedro Figueira, Thierry Forveille, Malcolm Fridlund, Guillaume Gaisné, Elisa Goffo, Iskra Georgieva, Sascha Grziwa, Eike Guenther, Artie P Hatzes, Marshall C. Johnson, Petr Kabáth, Emil Knudstrup , J udith Korth, Pablo Lewin, Jack J. Lissauer, Christophe Lovis, Rafael Luque, Claudio Melo, Edward H. Morgan, Robert Morris, Michel Mayor, Norio Narita, Hannah LM Osborne, Enric Palle, Francesco Pepe, Carina M. Persson , Samuel N. Quinn, Heike Rauer, Seth Redfield, Joshua E. Schlieder, Damien Ségransan, Luisa M. Serrano, Jeffrey C. Smith, Ján Å ubjak, Joseph D. Twicken, Stéphane Udry, Vincent Van Eylen and Michael Vezie, December 2 2021, Science.
DOI: 10.1126 / science.aay3253

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