Gliese 486 b A detailed analysis of the Gl 486 planetary system (Caballero et al. 2022, Astronomy and Astrophysics) *** The best studied terrestrial planet outside the Solar System *** FAQ * What have you discovered? Nothing really new. * So what are you presenting? A detailed analysis of a nearby exoearth. * Is it habitable? No. Our models predict that it is too hot. * Then, WHY ARE YOU MAKING A PRESS RELEASE? Because this exoearth is the Earth-like planet outside the Solar System that is best known to date. Mostly from seismology, we have interior models of the Earth, which has a core mostly made of iron surrounded by a mantle of solid and molten rocks. From their orbits and gravimetry, we have interior models of Mercury, Venus, Mars and the largest moons in the Solar System. Some of them, such as Mercury, have a huge metallic nucleus, while others, such as the Galilean moons around Jupiter or Titan around Saturn, may have none. Now, with ultra-precise spectroscopy and transit photometry, we open the window to modelling the interior of exoplanets in other solar systems, and investigating their structure and composition. * And can you infer the sizes of the nucleus and mantle of an exoplanet? Exactly. According to our models, our exoplanet, namely Gliese 486 b, has an iron nucleus that is proportionally smaller than Earth's, and that is surrounded by a deep mantle made of silicates and, perhaps, water. * How do you know that? Because we have excellent data. We used two high-precision spectrographs, CARMENES in Spain and MAROON-X in the USA, and two space missions, NASA's TESS and ESA's CHEOPS. With the spectrographs we measured the mass of the planet, while with the space missions we measured its radius. With mass and radius, we determined the exoplanet's density and computed our interior models. * Is it the first time to do it? Actually, it has been done in some planets before, but not in planets so small as ours nor with our accuracy and precision. Instead of by our data, our accuracy and precision are limited by those of the mass and radius of its star. But... * But what? We have measured the radius of the star! * Is it not always done? Nope. Usually, the radius of the star is estimated from certain observables. In our case, we measured directly the radius of the star with the CHARA Array, with is an near-infrared interferometer in the US. * It seems that you have done a lot of complicated things. What else have you done? We have re-determined the star's rotation period, measured its composition for the first time, looked for additional companions at a wide range of separations, quantified its activity... * I have read that some stars are very active and have large storms that can erode the atmospheres of close exoplanets! You are correct. Actually, our planet is very close to its star, which is an M dwarf. These M dwarfs, the smallest and most frequent stars, are in general quite active. However, we have plenty of data, some of them collected with the Hubble Space Telescope, that demonstrate that the star is rather inactive. * So could the planet have an atmosphere? Yes, it could. In our paper, we discuss what the James Webb Space Telescope will see when it observes our planet next year: hydrogen and helium, carbon dioxide, water steam, nitrogen, a very rarified atmosphere, no atmosphere at all... We have our favourite atmosphere scenario (see the video), but we must wait for a year to know how it really is. * [1 min later] Oh, what a nice video! Thank you. It was done by RenderArea. * Can you tell me again the name of the star? Gliese 486 [/GLEE-seh/ four-eight-six]. * And of the exoplanet? Gliese 486 b [/GLEE-seh/ four-eight-six /bee/]. * Can we send a probe there? I already told you last year! Not with current technology. Travelling all the time at 10% the speed of light, a probe would take 260 years to reach Gliese 486. So take care now of our Earth, because there is no "Planet b". * Just to finish: apart from "Gliese 486 b being the best studied terrestrial planet outside the Solar System", what do you like the most of your paper? I like that it will become an example of how to do this kind of analyses: bit by bit. "Despacito y con buena letra". * Para el lector español, ¿por qué estos resultados sobre Gliese 486 b son tan relevantes? El primer y segundo autores del artículo son españoles. Seis de los trece primeros autores, antes de que empiece el orden alfabético, son españoles. De los 67 autores, 23 (algo más de un tercio) son españoles. Hemos usado datos obtenidos con CARMENES, un instrumento hispano-alemán en el observatorio de Calar Alto, en Almería; con CHEOPS, una misión espacial construida y ensamblada por Airbus en Getafe y operada por INTA desde Torrejón de Ardoz; con telescopios ópticos de los observatorios de Sierra Nevada, en Granada, y Montcabrer, en Lleida... Hasta hace unos pocos años, los españoles decíamos "Que inventen (o descubran) ellos"; ahora, ¡somos el Rafa Nadal de la astrofísica mundial!.