Discovery of a lava and iron planet

Smaller than the earth, this star is surmounted by a melted surface mantle and is the astronomers call “a planet magma”. The conditions of its training remain mysterious.

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During its last update, made Wednesday 1 er December, the exoplanet.eu website, better known as the Encyclopedia of the Extrasolary Planets, had 4,878 entries. It will be necessary to add 4 879 e with the discovery, announced in Science Thursday, December 2, by an international team, a curious extrasolary planet. A lava and iron planet.

The star in question is one of the TESS, Spatial Telescope launched by NASA in 2018 to monitor small nearby stars, hoping that potential terrestrial exoplanets pass in front of them and temporarily do – and very slightly – Decrease their flow of light. A mode of detection called “transit technique”. The New Venue is named GJ-367B, because it revolves around GJ-367, a star located 30.7 light-years from us – as well as in the suburbs of the solar system, if we consider that our galaxy , the Milky Way, extends over some 100,000 light-years. Half less fat and less massive than the sun, GJ-367 belongs to the category of the red dwarfs, which are the lightest stars, the less warm and the least bright, but also the most abundant of the galaxy.

As one of the co-authors of the study explains, Xavier Delfosse, the Institute of Planetology and Astrophysics of Grenoble (CNRS-University Grenoble-Alpes), when an exoplanet is discovered, “the objective It is to get both mass and radius, to determine its density and thus have information about its composition “. The density constitutes, in fact, a primordial factor of which the planets are deduced from: if we draw on the stars of the solar system, “a rocky planet like the earth has a density of 5.5 grams per cube centimeter, continues Xavier Delfosse. For neptune-type planets, which have an ice core surrounded by a gas envelope, the density is between 1.5 g / cm 3 and 2 g / cm 3 while the gasents like Jupiter or Saturn, with a large atmosphere of hydrogen and helium, have a density that revolves around 1 g / cm 3 . “

The surface temperature is around 1,500 ° C

The transit technique gave the GJ-367B radius: 70% of the Earth’s radius. As for the mass, it was obtained thanks to the other method of detecting exoplanets, called “radial speeds”, which analyzes the tiny oscillations that the mass of the planet makes undergo to the position of his star. The researchers have thus been able to calculate the density of GJ-367B and have not been disappointed with the result: 8.1 g / cm 3 , a figure greater than that of the planets of the solar system and a figure close to iron density.

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/Media reports.