Gliese 486 b A nearby transiting rocky exoplanet that is suitable for atmospheric characterization (Trifonov et al. 2021, Science) FAQ * What have you found? A remarkable, very nearby, transiting, warm super-Earth with precise mass and radius determination. * A what? An exoplanet around a star close to the Sun that has a temperature similar to that of the surface of Venus, and that is remarkable for exoplanetology. * Is it habitable? No * Then, why is it remarkable? For a number of reasons. It is the third closest transiting exoplanet to Earth, but the closest one with mass determination and around an M dwarf... * Wait! Why is it important that the planet is "transiting", has a mass determination, and orbits around an "M dwarf"? Only if it transits then we can measure the planet radius and detect/investigate its atmosphere. Only if it has a mass determination (with the radial velocity method), together with its radius, then we can measure the planet density and infer its internal structure (i.e. metal core-silicate mantle ratio), as well as model its atmosphere [for experts: determine atmosphere scale height]. Only if the star is small, as M dwarfs are, then we can measure precise masses and radii of a few Earth units. As a result, a transiting exoplanet around an M dwarf with a mass determination is the best target to determine the composition of both the atmosphere and interior on an Earth-size exoplanet. But our planet is remarkable for more reasons. * Which reasons? Of the few "transiting exoplanets around an M dwarf with a mass determination", it orbits a relatively bright (in the optical and near-infrared) star, which ease follow-up observations; it has the most precise mass and radius determination, only comparable to those of the famous TRAPPIST-1 system, whose planet masses come from transit time variations; it has the right equilibrium temperature for transmission and, especially, emission spectroscopy with the JWST: warm enough to probably have a detectable atmosphere but cold enough not to liquify its surface; it orbits its star at the right separation: close enough to have a short orbital period (and maxmize the chances of observing it from the Earth) but far enough to survive its host star's flares... * Ey! I know that M-dwarf planets have "problems"? They always offer the same face to their star, which besides are magnetically active. Correct. The exoplanet is tidally locked to its star, which however is weakly active [for experts: small rotational velocity upper limit, long rotational period, faint Halpha and x-ray emission...]. * Do you really think that the exoplanet has an atmosphere? We do not know yet. It is a matter to be investigated with the forthcoming James Webb Space Telescope. Since the planet surface gravity is relatively high (~1.7 g), we believe that it may have retained an appreciable atmosphere. If our exoplanet does not have an atmosphere, then very few other Earth-size exoplanets will have! * OK, I start to get convinced. What is the name of the exoplanet? Gliese 486 b [/GLEE-seh/ four-eight-six b]. * Why that name? Because it is the first exoplanet discovered around the star Gliese 486. Wilhelm Gliese published in Heidelberg the first versions of a widely used Catalogue of Nearby Stars, which tabulates this star with the number 486. We follow the exoplanet nomenclature rules of the International Astronomical Union. However, the star was discovered over a century ago from Heidelberg by another German astronomer, Max Wolf, who tabulated the star with the number 437. Therefore, we could have baptised the planet "Wolf 437 b". * The first author of your discovery paper works in Heidelberg, too. Does it mean that the exoplanet is German? Absolutely not! The exoplanet Gliese 486 b was discovered by an international team of astronomers. For example, the first author is Bulgarian and works in Germany, the second and third are Spanish and work in Spain, and the fourth one is German and works in the USA. The team includes almost 70 researchers from Germany, Spain, USA, UK, Bulgaria, Finland, Italy, Philippines, Chile, Japan, Ireland, Iran, UK, Israel, just to cite a few. The first radial-velocity signal was detected with CARMENES, a German-Spanish instrument at a telescope in the south of Spain, but the transit was discovered by the NASA TESS space mission, and the brand-new MAROON-X spectrograph at a large telescope in US mainland gave the most precise radial-velocities, with which we determined a very precise planet mass. Besides, we used a plethora of other smaller telescopes and instruments, such as the Japanese-Spanish MuSCAT2 and the US Las Cumbres Observatory [here you add yours if not mentioned]. * How old is the planetary system? It has an age quite similar to that of the Sun with generous uncertainties. It is neither very young because of its weak activity (young stars rotate fast) nor very old because of its Galactic kinematics (it belongs to the thin disk) and metallicity (roughly solar). * Are there more planets around Gliese 486? We do not know yet. However, given the high frequency of multi-planetary systems around M dwarfs, we suspect that there are more planets awaiting to be discovered. * Are you planning observing further the system? Of course. We will start soon observations with the ESA space mission CHEOPS for improving the radius determination, while we may also improve the mass determination with new MAROON-X data. With them, we will be able to determine the structure and internal composition of the planet with an accuracy never reached in an Earth-size planet. Besides, JWST might observe it in Cycle 1. Other facilities, both on the ground or in space, can also be used for improving the knowledge of the system, but we prefer not to make it public yet, if you do not mind. * Can we send a probe there? Not with current technology. Travelling all the time at 10% the speed of light, a probe would take 260 years to reach Gliese 486. * Any trick for remembering its name? For the oldies: "Intel 80486", FOUR-EIGHT-SIX, the processor just before the Pentium.