Scientists have classified the exoplanet GJ 523b as a “mega-Earth”, a rocky planet with a radius of at least 2.1 Earth radii and density of at least 5.5 g/cm³. GJ 523b is about 2.55 times Earth’s radius, 23.5 Earth masses and about 7.8 g/cm³ dense. It circles a mid-K dwarf star every 17.75 days, with an equilibrium temperature near 538 K. Its features came from NASA’s Transiting Exoplanet Survey Satellite (TESS) transit data and radial velocity readings from the NEID spectrograph on the WIYN 3.5-metre Telescope. The 169-million-year-old system challenges the expectation that such a massive planet would hold a thick gas envelope.