Free Astronomy Magazine November-December 2022

42 NOVEMBER-DECEMBER 2022 ASTRO PUBLISHING of three super-Earths with a signifi- cant atmosphere and two super- Mercuries, which are the closest planets to the star.” The five planets in the HD 23472 sys- tem, three of which with masses smaller than the Earth, are among the lightest exoplanets whose masses were measured using the ra- dial velocity method. This technique detects tiny variations in the veloc- ity of a star in the line of sight due to the motion induced by an orbit- ing planet. The discovery was made possible thanks to the very high pre- cision of the ESPRESSO spectrograph mounted on the Very Large Tele- scope (VLT) at the European South- ern Observatory (ESO) in Chile. Super-Earths and super-Mercuries are the higher mass analogs of the Earth and Mercury in terms of com- position. They differ in that super- Mercuries have a bigger iron con- tent (and iron core). These types of exoplanets are very rare. In fact, only eight are known, counting the two recently discovered ones. Mercury is one of the densest plan- ets in the Solar System and it is not known why it has a relatively larger and more massive core than the Earth and other planets in our plan- etary system. Some possible ex- by IAC - Outreach Unit A system with three super-Earths and two super-Mercuries A n international science team has found a system orbiting the cool star HD 23472 with three super-Earths and two super- Mercuries. “We wanted to observe this planetary system to character- ize the composition of small planets and to study the transition between having or not having an atmos- phere, which could be related to the evaporation of the atmosphere due to the irradiation of the star,” explains Susana Barros, researcher at the Instituto de Astrofísica e Ciências do Espaço’s (IA) who led the study. “Surprisingly, the team found that this system is composed