In search of a ‘second Earth’, astronomers discover a hot, dense planet with an eight-hour year

An illustration of a red dwarf star orbiting an exoplanet. Credit: NASA/ESA/G. Bacon (STScI)

An international team of researchers has discovered a new planet, GJ 367 b, whose surface temperature can reach 1,500 degrees centigrade – hot enough to melt all rocks and metals – and which takes only eight hours to orbit around of his star.

In a new study published in the Science journal, researchers show that the planet, located 31 light-years from Earth, is one of the lightest of the roughly 5,000 exoplanets (planets outside our own solar system) known today, with half of the mass of the Earth. It has a diameter of just over 9,000 kilometers – slightly larger than " data-gt-translate-attributes="[{" attribute="">March.

The team says the research represents a step forward in the search for a “second Earth” as it shows that astronomers can determine the properties of even very small planets.

Co-author Dr Vincent Van Eylen (UCL Mullard Space Science Laboratory) said: “In this new study, the size and mass of the planet were calculated using two methods, both of which involved d analyze the starlight of the planet. One was to measure the tiny drop in light emitted by the star as the planet passed in front of it. This was done using data from " data-gt-translate-attributes="[{" attribute="">NasaTransiting exoplanet study satellite (TESS).

“The other method was to infer the mass of the planet from the effect it had on the motion of the star. This motion was slight – at a speed of 80 cm per second it was not more than walking speed – so it’s fantastic that we were able to detect this small movement 31 light years away.

Underground planet GJ 367b

Artist’s impression of the newly discovered planet. Credit: SPP 1992 (Patricia Klein)

The study involved 78 researchers and was led by astronomers from the Institute for Planetary Research at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR).

Lead author Dr Kristine Lam of DLR said: “Based on the precise determination of its radius and mass, GJ 367b is classified as a rocky planet. This places it among the subterrestrial-sized terrestrial planets and advances research in the search for a “second Earth”.

GJ 367 b belongs to the group of “ultra-short period” (USP) exoplanets that orbit their star in less than 24 hours. “We already know a few of them, but their origins are currently unknown,” Dr Lam said. “By measuring the precise fundamental properties of the USP planet, we can gain insight into the system’s formation and evolutionary history.”

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 HARPS instrument of the 3.6 m telescope of the European Southern Observatory.

With the combination of different evaluation methods, the radius and mass of the planet have been determined: its radius is 72% of the radius of the Earth and its mass is 55% of the mass of the Earth.

By determining its radius and its mass with a precision of 7 and 14% respectively, the researchers were also able to draw conclusions about the exoplanetthe internal structure. It is a rocky planet of low mass, but with a higher density than Earth. “The high density indicates that the planet is dominated by an iron core,” said Dr Szilárd Csizmadia.

“These properties are similar to those of Mercury, with its disproportionate iron and nickel core setting it apart from other terrestrial bodies in the solar system.”

However, the planet’s proximity to its star means that it is exposed to an extremely high level of radiation, more than 500 times stronger than what Earth experiences. The surface temperature could reach up to 1500 degrees Celsius – a temperature at which all rocks and metals would melt.

The parent 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 from the orbiting planet is particularly significant. 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 exoplanet research.

Researchers estimate that these red dwarfs, also known as “M-class stars,” orbit an average of two to three planets, each of which is at most four times the size of Earth.

To learn more about this discovery, read Sub-Earth Planet Discovered by Astronomers: Boiling New World Is Ultra-Light and Super-Fast.

Reference: “GJ 367b: an ultra-short period dense subterranean planet transiting a nearby 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, Pe tr 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 Šubjak, Joseph D. Twicken, Stéphane Udry, Vincent Van Eylen and Michael Vezie, December 2, 2021, Science.
DOI: 10.1126/science.aay3253

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